Configuration Manual

This document covers the configuration language as implemented in the version
specified above. It does not provide any hints, examples, or advice. For such
documentation, please refer to the Reference Manual or the Architecture Manual.
The summary below is meant to help you find sections by name and navigate
through the document.

Note to documentation contributors :
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When HAProxy is running in HTTP mode, both the request and the response are
fully analyzed and indexed, thus it becomes possible to build matching criteria
on almost anything found in the contents.

However, it is important to understand how HTTP requests and responses are
formed, and how HAProxy decomposes them. It will then become easier to write
correct rules and to debug existing configurations.

The HTTP protocol is transaction-driven. This means that each request will lead
to one and only one response. Traditionally, a TCP connection is established
from the client to the server, a request is sent by the client through the
connection, the server responds, and the connection is closed. A new request
will involve a new connection :

  [CON1] [REQ1] ... [RESP1] [CLO1] [CON2] [REQ2] ... [RESP2] [CLO2] ...

In this mode, called the "HTTP close" mode, there are as many connection
establishments as there are HTTP transactions. Since the connection is closed
by the server after the response, the client does not need to know the content
length.

Due to the transactional nature of the protocol, it was possible to improve it
to avoid closing a connection between two subsequent transactions. In this mode
however, it is mandatory that the server indicates the content length for each
response so that the client does not wait indefinitely. For this, a special
header is used: "Content-length". This mode is called the "keep-alive" mode :

  [CON] [REQ1] ... [RESP1] [REQ2] ... [RESP2] [CLO] ...

Its advantages are a reduced latency between transactions, and less processing
power required on the server side. It is generally better than the close mode,
but not always because the clients often limit their concurrent connections to
a smaller value.

Another improvement in the communications is the pipelining mode. It still uses
keep-alive, but the client does not wait for the first response to send the
second request. This is useful for fetching large number of images composing a
page :

  [CON] [REQ1] [REQ2] ... [RESP1] [RESP2] [CLO] ...

This can obviously have a tremendous benefit on performance because the network
latency is eliminated between subsequent requests. Many HTTP agents do not
correctly support pipelining since there is no way to associate a response with
the corresponding request in HTTP. For this reason, it is mandatory for the
server to reply in the exact same order as the requests were received.

The next improvement is the multiplexed mode, as implemented in HTTP/2. This
time, each transaction is assigned a single stream identifier, and all streams
are multiplexed over an existing connection. Many requests can be sent in
parallel by the client, and responses can arrive in any order since they also
carry the stream identifier.

By default HAProxy operates in keep-alive mode with regards to persistent
connections: for each connection it processes each request and response, and
leaves the connection idle on both sides between the end of a response and the
start of a new request. When it receives HTTP/2 connections from a client, it
processes all the requests in parallel and leaves the connection idling,
waiting for new requests, just as if it was a keep-alive HTTP connection.

HAProxy supports 4 connection modes :
  - keep alive    : all requests and responses are processed (default)
  - tunnel        : only the first request and response are processed,
                    everything else is forwarded with no analysis (deprecated).
  - server close  : the server-facing connection is closed after the response.
  - close         : the connection is actively closed after end of response.

First, let's consider this HTTP request :

  Line     Contents
  number
     1     GET /serv/login.php?lang=en&profile=2 HTTP/1.1
     2     Host: www.mydomain.com
     3     User-agent: my small browser
     4     Accept: image/jpeg, image/gif
     5     Accept: image/png

Line 1 is the "request line". It is always composed of 3 fields :

  - a METHOD      : GET
  - a URI         : /serv/login.php?lang=en&profile=2
  - a version tag : HTTP/1.1

All of them are delimited by what the standard calls LWS (linear white spaces),
which are commonly spaces, but can also be tabs or line feeds/carriage returns
followed by spaces/tabs. The method itself cannot contain any colon (':') and
is limited to alphabetic letters. All those various combinations make it
desirable that HAProxy performs the splitting itself rather than leaving it to
the user to write a complex or inaccurate regular expression.

The URI itself can have several forms :

  - A "relative URI" :

      /serv/login.php?lang=en&profile=2

    It is a complete URL without the host part. This is generally what is
    received by servers, reverse proxies and transparent proxies.

  - An "absolute URI", also called a "URL" :

      http://192.168.0.12:8080/serv/login.php?lang=en&profile=2

    It is composed of a "scheme" (the protocol name followed by '://'), a host
    name or address, optionally a colon (':') followed by a port number, then
    a relative URI beginning at the first slash ('/') after the address part.
    This is generally what proxies receive, but a server supporting HTTP/1.1
    must accept this form too.

  - a star ('*') : this form is only accepted in association with the OPTIONS
    method and is not relayable. It is used to inquiry a next hop's
    capabilities.

  - an address:port combination : 192.168.0.12:80
    This is used with the CONNECT method, which is used to establish TCP
    tunnels through HTTP proxies, generally for HTTPS, but sometimes for
    other protocols too.

In a relative URI, two sub-parts are identified. The part before the question
mark is called the "path". It is typically the relative path to static objects
on the server. The part after the question mark is called the "query string".
It is mostly used with GET requests sent to dynamic scripts and is very
specific to the language, framework or application in use.

HTTP/2 doesn't convey a version information with the request, so the version is
assumed to be the same as the one of the underlying protocol (i.e. "HTTP/2").

The headers start at the second line. They are composed of a name at the
beginning of the line, immediately followed by a colon (':'). Traditionally,
an LWS is added after the colon but that's not required. Then come the values.
Multiple identical headers may be folded into one single line, delimiting the
values with commas, provided that their order is respected. This is commonly
encountered in the "Cookie:" field. A header may span over multiple lines if
the subsequent lines begin with an LWS. In the example in 1.2, lines 4 and 5
define a total of 3 values for the "Accept:" header.

Contrary to a common misconception, header names are not case-sensitive, and
their values are not either if they refer to other header names (such as the
"Connection:" header). In HTTP/2, header names are always sent in lower case,
as can be seen when running in debug mode. Internally, all header names are
normalized to lower case so that HTTP/1.x and HTTP/2 use the exact same
representation, and they are sent as-is on the other side. This explains why an
HTTP/1.x request typed with camel case is delivered in lower case.

The end of the headers is indicated by the first empty line. People often say
that it's a double line feed, which is not exact, even if a double line feed
is one valid form of empty line.

Fortunately, HAProxy takes care of all these complex combinations when indexing
headers, checking values and counting them, so there is no reason to worry
about the way they could be written, but it is important not to accuse an
application of being buggy if it does unusual, valid things.

Important note:
   As suggested by RFC7231, HAProxy normalizes headers by replacing line breaks
   in the middle of headers by LWS in order to join multi-line headers. This
   is necessary for proper analysis and helps less capable HTTP parsers to work
   correctly and not to be fooled by such complex constructs.

An HTTP response looks very much like an HTTP request. Both are called HTTP
messages. Let's consider this HTTP response :

  Line     Contents
  number
     1     HTTP/1.1 200 OK
     2     Content-length: 350
     3     Content-Type: text/html

As a special case, HTTP supports so called "Informational responses" as status
codes 1xx. These messages are special in that they don't convey any part of the
response, they're just used as sort of a signaling message to ask a client to
continue to post its request for instance. In the case of a status 100 response
the requested information will be carried by the next non-100 response message
following the informational one. This implies that multiple responses may be
sent to a single request, and that this only works when keep-alive is enabled
(1xx messages are HTTP/1.1 only). HAProxy handles these messages and is able to
correctly forward and skip them, and only process the next non-100 response. As
such, these messages are neither logged nor transformed, unless explicitly
state otherwise. Status 101 messages indicate that the protocol is changing
over the same connection and that haproxy must switch to tunnel mode, just as
if a CONNECT had occurred. Then the Upgrade header would contain additional
information about the type of protocol the connection is switching to.

Line 1 is the "response line". It is always composed of 3 fields :

  - a version tag : HTTP/1.1
  - a status code : 200
  - a reason      : OK

The status code is always 3-digit. The first digit indicates a general status :
 - 1xx = informational message to be skipped (e.g. 100, 101)
 - 2xx = OK, content is following   (e.g. 200, 206)
 - 3xx = OK, no content following   (e.g. 302, 304)
 - 4xx = error caused by the client (e.g. 401, 403, 404)
 - 5xx = error caused by the server (e.g. 500, 502, 503)

Please refer to RFC7231 for the detailed meaning of all such codes. The
"reason" field is just a hint, but is not parsed by clients. Anything can be
found there, but it's a common practice to respect the well-established
messages. It can be composed of one or multiple words, such as "OK", "Found",
or "Authentication Required".

HAProxy may emit the following status codes by itself :

  Code  When / reason
   200  access to stats page, and when replying to monitoring requests
   301  when performing a redirection, depending on the configured code
   302  when performing a redirection, depending on the configured code
   303  when performing a redirection, depending on the configured code
   307  when performing a redirection, depending on the configured code
   308  when performing a redirection, depending on the configured code
   400  for an invalid or too large request
   401  when an authentication is required to perform the action (when
        accessing the stats page)
   403  when a request is forbidden by a "block" ACL or "reqdeny" filter
   408  when the request timeout strikes before the request is complete
   500  when haproxy encounters an unrecoverable internal error, such as a
        memory allocation failure, which should never happen
   502  when the server returns an empty, invalid or incomplete response, or
        when an "rspdeny" filter blocks the response.
   503  when no server was available to handle the request, or in response to
        monitoring requests which match the "monitor fail" condition
   504  when the response timeout strikes before the server responds

The error 4xx and 5xx codes above may be customized (see "errorloc" in section
4.2).

Response headers work exactly like request headers, and as such, HAProxy uses
the same parsing function for both. Please refer to paragraph 1.2.2 for more
details.

HAProxy's configuration process involves 3 major sources of parameters :

  - the arguments from the command-line, which always take precedence
  - the "global" section, which sets process-wide parameters
  - the proxies sections which can take form of "defaults", "listen",
    "frontend" and "backend".

The configuration file syntax consists in lines beginning with a keyword
referenced in this manual, optionally followed by one or several parameters
delimited by spaces.

HAProxy's configuration introduces a quoting and escaping system similar to
many programming languages. The configuration file supports 3 types: escaping
with a backslash, weak quoting with double quotes, and strong quoting with
single quotes.

If spaces have to be entered in strings, then they must be escaped by preceding
them by a backslash ('\') or by quoting them. Backslashes also have to be
escaped by doubling or strong quoting them.

Escaping is achieved by preceding a special character by a backslash ('\'):

  \    to mark a space and differentiate it from a delimiter
  \#   to mark a hash and differentiate it from a comment
  \\   to use a backslash
  \'   to use a single quote and differentiate it from strong quoting
  \"   to use a double quote and differentiate it from weak quoting

Weak quoting is achieved by using double quotes (""). Weak quoting prevents
the interpretation of:

       space as a parameter separator
  '    single quote as a strong quoting delimiter
  #    hash as a comment start

Weak quoting permits the interpretation of variables, if you want to use a non
-interpreted dollar within a double quoted string, you should escape it with a
backslash ("\$"), it does not work outside weak quoting.

Interpretation of escaping and special characters are not prevented by weak
quoting.

Strong quoting is achieved by using single quotes (''). Inside single quotes,
nothing is interpreted, it's the efficient way to quote regexes.

Quoted and escaped strings are replaced in memory by their interpreted
equivalent, it allows you to perform concatenation.

# those are equivalents:
log-format %{+Q}o\ %t\ %s\ %{-Q}r
log-format "%{+Q}o %t %s %{-Q}r"
log-format '%{+Q}o %t %s %{-Q}r'
log-format "%{+Q}o %t"' %s %{-Q}r'
log-format "%{+Q}o %t"' %s'\ %{-Q}r

# those are equivalents:
reqrep "^([^\ :]*)\ /static/(.*)"     \1\ /\2
reqrep "^([^ :]*)\ /static/(.*)"     '\1 /\2'
reqrep "^([^ :]*)\ /static/(.*)"     "\1 /\2"
reqrep "^([^ :]*)\ /static/(.*)"     "\1\ /\2"

HAProxy's configuration supports environment variables. Those variables are
interpreted only within double quotes. Variables are expanded during the
configuration parsing. Variable names must be preceded by a dollar ("$") and
optionally enclosed with braces ("{}") similarly to what is done in Bourne
shell. Variable names can contain alphanumerical characters or the character
underscore ("_") but should not start with a digit.

bind "fd@${FD_APP1}"

log "${LOCAL_SYSLOG}:514" local0 notice   # send to local server

user "$HAPROXY_USER"

A special variable $HAPROXY_LOCALPEER is defined at the startup of the process
which contains the name of the local peer. (See "-L" in the management guide.)

Some parameters involve values representing time, such as timeouts. These
values are generally expressed in milliseconds (unless explicitly stated
otherwise) but may be expressed in any other unit by suffixing the unit to the
numeric value. It is important to consider this because it will not be repeated
for every keyword. Supported units are :

  - us : microseconds. 1 microsecond = 1/1000000 second
  - ms : milliseconds. 1 millisecond = 1/1000 second. This is the default.
  - s  : seconds. 1s = 1000ms
  - m  : minutes. 1m = 60s = 60000ms
  - h  : hours.   1h = 60m = 3600s = 3600000ms
  - d  : days.    1d = 24h = 1440m = 86400s = 86400000ms

    # Simple configuration for an HTTP proxy listening on port 80 on all
    # interfaces and forwarding requests to a single backend "servers" with a
    # single server "server1" listening on 127.0.0.1:8000
    global
        daemon
        maxconn 256

    defaults
        mode http
        timeout connect 5000ms
        timeout client 50000ms
        timeout server 50000ms

    frontend http-in
        bind *:80
        default_backend servers

    backend servers
        server server1 127.0.0.1:8000 maxconn 32


    # The same configuration defined with a single listen block. Shorter but
    # less expressive, especially in HTTP mode.
    global
        daemon
        maxconn 256

    defaults
        mode http
        timeout connect 5000ms
        timeout client 50000ms
        timeout server 50000ms

    listen http-in
        bind *:80
        server server1 127.0.0.1:8000 maxconn 32


Assuming haproxy is in $PATH, test these configurations in a shell with:

    $ sudo haproxy -f configuration.conf -c

Parameters in the "global" section are process-wide and often OS-specific. They
are generally set once for all and do not need being changed once correct. Some
of them have command-line equivalents.

The following keywords are supported in the "global" section :

 * Process management and security
   - ca-base
   - chroot
   - crt-base
   - cpu-map
   - daemon
   - description
   - deviceatlas-json-file
   - deviceatlas-log-level
   - deviceatlas-separator
   - deviceatlas-properties-cookie
   - external-check
   - gid
   - group
   - hard-stop-after
   - log
   - log-tag
   - log-send-hostname
   - lua-load
   - nbproc
   - nbthread
   - node
   - pidfile
   - presetenv
   - resetenv
   - uid
   - ulimit-n
   - user
   - set-dumpable
   - setenv
   - stats
   - ssl-default-bind-ciphers
   - ssl-default-bind-ciphersuites
   - ssl-default-bind-options
   - ssl-default-server-ciphers
   - ssl-default-server-ciphersuites
   - ssl-default-server-options
   - ssl-dh-param-file
   - ssl-server-verify
   - unix-bind
   - unsetenv
   - 51degrees-data-file
   - 51degrees-property-name-list
   - 51degrees-property-separator
   - 51degrees-cache-size
   - wurfl-data-file
   - wurfl-information-list
   - wurfl-information-list-separator
   - wurfl-engine-mode
   - wurfl-cache-size
   - wurfl-useragent-priority

 * Performance tuning
   - max-spread-checks
   - maxconn
   - maxconnrate
   - maxcomprate
   - maxcompcpuusage
   - maxpipes
   - maxsessrate
   - maxsslconn
   - maxsslrate
   - maxzlibmem
   - noepoll
   - nokqueue
   - nopoll
   - nosplice
   - nogetaddrinfo
   - noreuseport
   - profiling.tasks
   - spread-checks
   - server-state-base
   - server-state-file
   - ssl-engine
   - ssl-mode-async
   - tune.buffers.limit
   - tune.buffers.reserve
   - tune.bufsize
   - tune.chksize
   - tune.comp.maxlevel
   - tune.h2.header-table-size
   - tune.h2.initial-window-size
   - tune.h2.max-concurrent-streams
   - tune.http.cookielen
   - tune.http.logurilen
   - tune.http.maxhdr
   - tune.idletimer
   - tune.lua.forced-yield
   - tune.lua.maxmem
   - tune.lua.session-timeout
   - tune.lua.task-timeout
   - tune.lua.service-timeout
   - tune.maxaccept
   - tune.maxpollevents
   - tune.maxrewrite
   - tune.pattern.cache-size
   - tune.pipesize
   - tune.rcvbuf.client
   - tune.rcvbuf.server
   - tune.recv_enough
   - tune.runqueue-depth
   - tune.sndbuf.client
   - tune.sndbuf.server
   - tune.ssl.cachesize
   - tune.ssl.lifetime
   - tune.ssl.force-private-cache
   - tune.ssl.maxrecord
   - tune.ssl.default-dh-param
   - tune.ssl.ssl-ctx-cache-size
   - tune.ssl.capture-cipherlist-size
   - tune.vars.global-max-size
   - tune.vars.proc-max-size
   - tune.vars.reqres-max-size
   - tune.vars.sess-max-size
   - tune.vars.txn-max-size
   - tune.zlib.memlevel
   - tune.zlib.windowsize

 * Debugging
   - debug
   - quiet

Assigns a default directory to fetch SSL CA certificates and CRLs from when a
relative path is used with "ca-file" or "crl-file" directives. Absolute
locations specified in "ca-file" and "crl-file" prevail and ignore "ca-base".

Changes current directory to <jail dir> and performs a chroot() there before
dropping privileges. This increases the security level in case an unknown
vulnerability would be exploited, since it would make it very hard for the
attacker to exploit the system. This only works when the process is started
with superuser privileges. It is important to ensure that <jail_dir> is both
empty and non-writable to anyone.

On Linux 2.6 and above, it is possible to bind a process or a thread to a
specific CPU set. This means that the process or the thread will never run on
other CPUs. The "cpu-map" directive specifies CPU sets for process or thread
sets. The first argument is a process set, eventually followed by a thread
set. These sets have the format

    all | odd | even | number[-[number]]

<number>> must be a number between 1 and 32 or 64, depending on the machine's
word size. Any process IDs above nbproc and any thread IDs above nbthread are
ignored. It is possible to specify a range with two such number delimited by
a dash ('-'). It also is possible to specify all processes at once using
"all", only odd numbers using "odd" or even numbers using "even", just like
with the "bind-process" directive. The second and forthcoming arguments are
CPU sets. Each CPU set is either a unique number between 0 and 31 or 63 or a
range with two such numbers delimited by a dash ('-'). Multiple CPU numbers
or ranges may be specified, and the processes or threads will be allowed to
bind to all of them. Obviously, multiple "cpu-map" directives may be
specified. Each "cpu-map" directive will replace the previous ones when they
overlap. A thread will be bound on the intersection of its mapping and the
one of the process on which it is attached. If the intersection is null, no
specific binding will be set for the thread.

Ranges can be partially defined. The higher bound can be omitted. In such
case, it is replaced by the corresponding maximum value, 32 or 64 depending
on the machine's word size.

The prefix "auto:" can be added before the process set to let HAProxy
automatically bind a process or a thread to a CPU by incrementing
process/thread and CPU sets. To be valid, both sets must have the same
size. No matter the declaration order of the CPU sets, it will be bound from
the lowest to the highest bound. Having a process and a thread range with the
"auto:" prefix is not supported. Only one range is supported, the other one
must be a fixed number.

cpu-map 1-4 0-3   # bind processes 1 to 4 on the first 4 CPUs

cpu-map 1/all 0-3 # bind all threads of the first process on the
                  # first 4 CPUs

cpu-map 1- 0-     # will be replaced by "cpu-map 1-64 0-63"
                  # or "cpu-map 1-32 0-31" depending on the machine's
                  # word size.

# all these lines bind the process 1 to the cpu 0, the process 2 to cpu 1
# and so on.
cpu-map auto:1-4   0-3
cpu-map auto:1-4   0-1 2-3
cpu-map auto:1-4   3 2 1 0

# all these lines bind the thread 1 to the cpu 0, the thread 2 to cpu 1
# and so on.
cpu-map auto:1/1-4   0-3
cpu-map auto:1/1-4   0-1 2-3
cpu-map auto:1/1-4   3 2 1 0

# bind each process to exactly one CPU using all/odd/even keyword
cpu-map auto:all   0-63
cpu-map auto:even  0-31
cpu-map auto:odd   32-63

# invalid cpu-map because process and CPU sets have different sizes.
cpu-map auto:1-4   0    # invalid
cpu-map auto:1     0-3  # invalid

# invalid cpu-map because automatic binding is used with a process range
# and a thread range.
cpu-map auto:all/all   0 # invalid
cpu-map auto:all/1-4   0 # invalid
cpu-map auto:1-4/all   0 # invalid

Assigns a default directory to fetch SSL certificates from when a relative
path is used with "crtfile" directives. Absolute locations specified after
"crtfile" prevail and ignore "crt-base".

Makes the process fork into background. This is the recommended mode of
operation. It is equivalent to the command line "-D" argument. It can be
disabled by the command line "-db" argument. This option is ignored in
systemd mode.

Sets the path of the DeviceAtlas JSON data file to be loaded by the API.
The path must be a valid JSON data file and accessible by HAProxy process.

Sets the level of information returned by the API. This directive is
optional and set to 0 by default if not set.

Sets the character separator for the API properties results. This directive
is optional and set to | by default if not set.

Sets the client cookie's name used for the detection if the DeviceAtlas
Client-side component was used during the request. This directive is optional
and set to DAPROPS by default if not set.

Allows the use of an external agent to perform health checks.
This is disabled by default as a security precaution.
See "option external-check".

Changes the process' group ID to <number>. It is recommended that the group
ID is dedicated to HAProxy or to a small set of similar daemons. HAProxy must
be started with a user belonging to this group, or with superuser privileges.
Note that if haproxy is started from a user having supplementary groups, it
will only be able to drop these groups if started with superuser privileges.
See also "group" and "uid".

Similar to "gid" but uses the GID of group name <group name> from /etc/group.
See also "gid" and "user".

Defines the maximum time allowed to perform a clean soft-stop.

<time>  is the maximum time (by default in milliseconds) for which the
        instance will remain alive when a soft-stop is received via the
        SIGUSR1 signal.

This may be used to ensure that the instance will quit even if connections
remain opened during a soft-stop (for example with long timeouts for a proxy
in tcp mode). It applies both in TCP and HTTP mode.

global
  hard-stop-after 30s

Similar to "gid" but uses the GID of group name <group name> from /etc/group.
See also "gid" and "user".

Adds a global syslog server. Several global servers can be defined. They
will receive logs for starts and exits, as well as all logs from proxies
configured with "log global".

<address> can be one of:

      - An IPv4 address optionally followed by a colon and a UDP port. If
        no port is specified, 514 is used by default (the standard syslog
        port).

      - An IPv6 address followed by a colon and optionally a UDP port. If
        no port is specified, 514 is used by default (the standard syslog
        port).

      - A filesystem path to a datagram UNIX domain socket, keeping in mind
        considerations for chroot (be sure the path is accessible inside
        the chroot) and uid/gid (be sure the path is appropriately
        writable).

      - A file descriptor number in the form "fd@<number>", which may point
        to a pipe, terminal, or socket. In this case unbuffered logs are used
        and one writev() call per log is performed. This is a bit expensive
        but acceptable for most workloads. Messages sent this way will not be
        truncated but may be dropped, in which case the DroppedLogs counter
        will be incremented. The writev() call is atomic even on pipes for
        messages up to PIPE_BUF size, which POSIX recommends to be at least
        512 and which is 4096 bytes on most modern operating systems. Any
        larger message may be interleaved with messages from other processes.
        Exceptionally for debugging purposes the file descriptor may also be
        directed to a file, but doing so will significantly slow haproxy down
        as non-blocking calls will be ignored. Also there will be no way to
        purge nor rotate this file without restarting the process. Note that
        the configured syslog format is preserved, so the output is suitable
        for use with a TCP syslog server. See also the "short" and "raw"
        format below.

      - "stdout" / "stderr", which are respectively aliases for "fd@1" and
        "fd@2", see above.

      You may want to reference some environment variables in the address
      parameter, see section 2.3 about environment variables.

<length> is an optional maximum line length. Log lines larger than this value
         will be truncated before being sent. The reason is that syslog
         servers act differently on log line length. All servers support the
         default value of 1024, but some servers simply drop larger lines
         while others do log them. If a server supports long lines, it may
         make sense to set this value here in order to avoid truncating long
         lines. Similarly, if a server drops long lines, it is preferable to
         truncate them before sending them. Accepted values are 80 to 65535
         inclusive. The default value of 1024 is generally fine for all
         standard usages. Some specific cases of long captures or
         JSON-formatted logs may require larger values. You may also need to
         increase "tune.http.logurilen" if your request URIs are truncated.

<format> is the log format used when generating syslog messages. It may be
         one of the following :

  rfc3164   The RFC3164 syslog message format. This is the default.
            (https://tools.ietf.org/html/rfc3164)

  rfc5424   The RFC5424 syslog message format.
            (https://tools.ietf.org/html/rfc5424)

  short     A message containing only a level between angle brackets such as
            '<3>', followed by the text. The PID, date, time, process name
            and system name are omitted. This is designed to be used with a
            local log server. This format is compatible with what the systemd
            logger consumes.

  raw       A message containing only the text. The level, PID, date, time,
            process name and system name are omitted. This is designed to be
            used in containers or during development, where the severity only
            depends on the file descriptor used (stdout/stderr).

<facility> must be one of the 24 standard syslog facilities :

               kern   user   mail   daemon auth   syslog lpr    news
               uucp   cron   auth2  ftp    ntp    audit  alert  cron2
               local0 local1 local2 local3 local4 local5 local6 local7

           Note that the facility is ignored for the "short" and "raw"
           formats, but still required as a positional field. It is
           recommended to use "daemon" in this case to make it clear that
           it's only supposed to be used locally.

An optional level can be specified to filter outgoing messages. By default,
all messages are sent. If a maximum level is specified, only messages with a
severity at least as important as this level will be sent. An optional minimum
level can be specified. If it is set, logs emitted with a more severe level
than this one will be capped to this level. This is used to avoid sending
"emerg" messages on all terminals on some default syslog configurations.
Eight levels are known :

        emerg  alert  crit   err    warning notice info  debug

Sets the hostname field in the syslog header. If optional "string" parameter
is set the header is set to the string contents, otherwise uses the hostname
of the system. Generally used if one is not relaying logs through an
intermediate syslog server or for simply customizing the hostname printed in
the logs.

Sets the tag field in the syslog header to this string. It defaults to the
program name as launched from the command line, which usually is "haproxy".
Sometimes it can be useful to differentiate between multiple processes
running on the same host. See also the per-proxy "log-tag" directive.

This global directive loads and executes a Lua file. This directive can be
used multiple times.

Master-worker mode. It is equivalent to the command line "-W" argument.
This mode will launch a "master" which will monitor the "workers". Using
this mode, you can reload HAProxy directly by sending a SIGUSR2 signal to
the master. The master-worker mode is compatible either with the foreground
or daemon mode. It is recommended to use this mode with multiprocess and
systemd.
By default, if a worker exits with a bad return code, in the case of a
segfault for example, all workers will be killed, and the master will leave.
It is convenient to combine this behavior with Restart=on-failure in a
systemd unit file in order to relaunch the whole process. If you don't want
this behavior, you must use the keyword "no-exit-on-failure".

See also "-W" in the management guide.

Creates <number> processes when going daemon. This requires the "daemon"
mode. By default, only one process is created, which is the recommended mode
of operation. For systems limited to small sets of file descriptors per
process, it may be needed to fork multiple daemons. USING MULTIPLE PROCESSES
IS HARDER TO DEBUG AND IS REALLY DISCOURAGED. See also "daemon" and
"nbthread".

This setting is only available when support for threads was built in. It
creates <number> threads for each created processes. It means if HAProxy is
started in foreground, it only creates <number> threads for the first
process. See also "nbproc".

Writes PIDs of all daemons into file <pidfile>. This option is equivalent to
the "-p" command line argument. The file must be accessible to the user
starting the process. See also "daemon".

Sets environment variable <name> to value <value>. If the variable exists, it
is NOT overwritten. The changes immediately take effect so that the next line
in the configuration file sees the new value. See also "setenv", "resetenv",
and "unsetenv".

Removes all environment variables except the ones specified in argument. It
allows to use a clean controlled environment before setting new values with
setenv or unsetenv. Please note that some internal functions may make use of
some environment variables, such as time manipulation functions, but also
OpenSSL or even external checks. This must be used with extreme care and only
after complete validation. The changes immediately take effect so that the
next line in the configuration file sees the new environment. See also
"setenv", "presetenv", and "unsetenv".

Limits the stats socket to a certain set of processes numbers. By default the
stats socket is bound to all processes, causing a warning to be emitted when
nbproc is greater than 1 because there is no way to select the target process
when connecting. However, by using this setting, it becomes possible to pin
the stats socket to a specific set of processes, typically the first one. The
warning will automatically be disabled when this setting is used, whatever
the number of processes used. The maximum process ID depends on the machine's
word size (32 or 64). Ranges can be partially defined. The higher bound can
be omitted. In such case, it is replaced by the corresponding maximum
value. A better option consists in using the "process" setting of the "stats
socket" line to force the process on each line.

Specifies the directory prefix to be prepended in front of all servers state
file names which do not start with a '/'. See also "server-state-file",
"load-server-state-from-file" and "server-state-file-name".

Specifies the path to the file containing state of servers. If the path starts
with a slash ('/'), it is considered absolute, otherwise it is considered
relative to the directory specified using "server-state-base" (if set) or to
the current directory. Before reloading HAProxy, it is possible to save the
servers' current state using the stats command "show servers state". The
output of this command must be written in the file pointed by <file>. When
starting up, before handling traffic, HAProxy will read, load and apply state
for each server found in the file and available in its current running
configuration. See also "server-state-base" and "show servers state",
"load-server-state-from-file" and "server-state-file-name"

Sets environment variable <name> to value <value>. If the variable exists, it
is overwritten. The changes immediately take effect so that the next line in
the configuration file sees the new value. See also "presetenv", "resetenv",
and "unsetenv".

This option is better left disabled by default and enabled only upon a
developer's request. It has no impact on performance nor stability but will
try hard to re-enable core dumps that were possibly disabled by file size
limitations (ulimit -f), core size limitations (ulimit -c), or "dumpability"
of a process after changing its UID/GID (such as /proc/sys/fs/suid_dumpable
on Linux). Core dumps might still be limited by the current directory's
permissions (check what directory the file is started from), the chroot
directory's permission (it may be needed to temporarily disable the chroot
directive or to move it to a dedicated writable location), or any other
system-specific constraint. For example, some Linux flavours are notorious
for replacing the default core file with a path to an executable not even
installed on the system (check /proc/sys/kernel/core_pattern). Often, simply
writing "core", "core.%p" or "/var/log/core/core.%p" addresses the issue.
When trying to enable this option waiting for a rare issue to re-appear, it's
often a good idea to first try to obtain such a dump by issuing, for example,
"kill -11" to the haproxy process and verify that it leaves a core where
expected when dying.

This setting is only available when support for OpenSSL was built in. It sets
the default string describing the list of cipher algorithms ("cipher suite")
that are negotiated during the SSL/TLS handshake up to TLSv1.2 for all
"bind" lines which do not explicitly define theirs. The format of the string
is defined in "man 1 ciphers" from OpenSSL man pages. For background
information and recommendations see e.g.
(https://wiki.mozilla.org/Security/Server_Side_TLS) and
(https://mozilla.github.io/server-side-tls/ssl-config-generator/). For TLSv1.3
cipher configuration, please check the "ssl-default-bind-ciphersuites" keyword.
Please check the "bind" keyword for more information.

This setting is only available when support for OpenSSL was built in and
OpenSSL 1.1.1 or later was used to build HAProxy. It sets the default string
describing the list of cipher algorithms ("cipher suite") that are negotiated
during the TLSv1.3 handshake for all "bind" lines which do not explicitly define
theirs. The format of the string is defined in
"man 1 ciphers" from OpenSSL man pages under the section "ciphersuites". For
cipher configuration for TLSv1.2 and earlier, please check the
"ssl-default-bind-ciphers" keyword. Please check the "bind" keyword for more
information.

This setting is only available when support for OpenSSL was built in. It sets
default ssl-options to force on all "bind" lines. Please check the "bind"
keyword to see available options.

global
   ssl-default-bind-options ssl-min-ver TLSv1.0 no-tls-tickets

This setting is only available when support for OpenSSL was built in. It
sets the default string describing the list of cipher algorithms that are
negotiated during the SSL/TLS handshake up to TLSv1.2 with the server,
for all "server" lines which do not explicitly define theirs. The format of
the string is defined in "man 1 ciphers" from OpenSSL man pages. For background
information and recommendations see e.g.
(https://wiki.mozilla.org/Security/Server_Side_TLS) and
(https://mozilla.github.io/server-side-tls/ssl-config-generator/).
For TLSv1.3 cipher configuration, please check the
"ssl-default-server-ciphersuites" keyword. Please check the "server" keyword
for more information.

This setting is only available when support for OpenSSL was built in and
OpenSSL 1.1.1 or later was used to build HAProxy. It sets the default
string describing the list of cipher algorithms that are negotiated during
the TLSv1.3 handshake with the server, for all "server" lines which do not
explicitly define theirs. The format of the string is defined in
"man 1 ciphers" from OpenSSL man pages under the section "ciphersuites". For
cipher configuration for TLSv1.2 and earlier, please check the
"ssl-default-server-ciphers" keyword. Please check the "server" keyword for
more information.

This setting is only available when support for OpenSSL was built in. It sets
default ssl-options to force on all "server" lines. Please check the "server"
keyword to see available options.

This setting is only available when support for OpenSSL was built in. It sets
the default DH parameters that are used during the SSL/TLS handshake when
ephemeral Diffie-Hellman (DHE) key exchange is used, for all "bind" lines
which do not explicitly define theirs. It will be overridden by custom DH
parameters found in a bind certificate file if any. If custom DH parameters
are not specified either by using ssl-dh-param-file or by setting them
directly in the certificate file, pre-generated DH parameters of the size
specified by tune.ssl.default-dh-param will be used. Custom parameters are
known to be more secure and therefore their use is recommended.
Custom DH parameters may be generated by using the OpenSSL command
"openssl dhparam <size>", where size should be at least 2048, as 1024-bit DH
parameters should not be considered secure anymore.

The default behavior for SSL verify on servers side. If specified to 'none',
servers certificates are not verified. The default is 'required' except if
forced using cmdline option '-dV'.

Binds a UNIX socket to <path> or a TCPv4/v6 address to <address:port>.
Connections to this socket will return various statistics outputs and even
allow some commands to be issued to change some runtime settings. Please
consult section 9.3 "Unix Socket commands" of Management Guide for more
details.

All parameters supported by "bind" lines are supported, for instance to
restrict access to some users or their access rights. Please consult
section 5.1 for more information.

The default timeout on the stats socket is set to 10 seconds. It is possible
to change this value with "stats timeout". The value must be passed in
milliseconds, or be suffixed by a time unit among { us, ms, s, m, h, d }.

By default, the stats socket is limited to 10 concurrent connections. It is
possible to change this value with "stats maxconn".

Changes the process' user ID to <number>. It is recommended that the user ID
is dedicated to HAProxy or to a small set of similar daemons. HAProxy must
be started with superuser privileges in order to be able to switch to another
one. See also "gid" and "user".

Sets the maximum number of per-process file-descriptors to <number>. By
default, it is automatically computed, so it is recommended not to use this
option.

Fixes common settings to UNIX listening sockets declared in "bind" statements.
This is mainly used to simplify declaration of those UNIX sockets and reduce
the risk of errors, since those settings are most commonly required but are
also process-specific. The <prefix> setting can be used to force all socket
path to be relative to that directory. This might be needed to access another
component's chroot. Note that those paths are resolved before haproxy chroots
itself, so they are absolute. The <mode>, <user>, <uid>, <group> and <gid>
all have the same meaning as their homonyms used by the "bind" statement. If
both are specified, the "bind" statement has priority, meaning that the
"unix-bind" settings may be seen as process-wide default settings.

Removes environment variables specified in arguments. This can be useful to
hide some sensitive information that are occasionally inherited from the
user's environment during some operations. Variables which did not exist are
silently ignored so that after the operation, it is certain that none of
these variables remain. The changes immediately take effect so that the next
line in the configuration file will not see these variables. See also
"setenv", "presetenv", and "resetenv".

Similar to "uid" but uses the UID of user name <user name> from /etc/passwd.
See also "uid" and "group".

Only letters, digits, hyphen and underscore are allowed, like in DNS names.

This statement is useful in HA configurations where two or more processes or
servers share the same IP address. By setting a different node-name on all
nodes, it becomes easy to immediately spot what server is handling the
traffic.

Add a text that describes the instance.

Please note that it is required to escape certain characters (# for example)
and this text is inserted into a html page so you should avoid using
"<" and ">" characters.

The path of the 51Degrees data file to provide device detection services. The
file should be unzipped and accessible by HAProxy with relevant permissions.

Please note that this option is only available when haproxy has been
compiled with USE_51DEGREES.

A list of 51Degrees property names to be load from the dataset. A full list
of names is available on the 51Degrees website:
https://51degrees.com/resources/property-dictionary

Please note that this option is only available when haproxy has been
compiled with USE_51DEGREES.

A char that will be appended to every property value in a response header
containing 51Degrees results. If not set that will be set as ','.

Please note that this option is only available when haproxy has been
compiled with USE_51DEGREES.

Sets the size of the 51Degrees converter cache to <number> entries. This
is an LRU cache which reminds previous device detections and their results.
By default, this cache is disabled.

Please note that this option is only available when haproxy has been
compiled with USE_51DEGREES.

The path of the WURFL data file to provide device detection services. The
file should be accessible by HAProxy with relevant permissions.

Please note that this option is only available when haproxy has been compiled
with USE_WURFL=1.

A space-delimited list of WURFL capabilities, virtual capabilities, property
names we plan to use in injected headers. A full list of capability and
virtual capability names is available on the Scientiamobile website :

    https://www.scientiamobile.com/wurflCapability

Valid WURFL properties are:
- wurfl_id                    Contains the device ID of the matched device.

- wurfl_root_id               Contains the device root ID of the matched
                              device.

- wurfl_isdevroot             Tells if the matched device is a root device.
                              Possible values are "TRUE" or "FALSE".

- wurfl_useragent             The original useragent coming with this
                              particular web request.

- wurfl_api_version           Contains a string representing the currently
                              used Libwurfl API version.

- wurfl_engine_target         Contains a string representing the currently
                              set WURFL Engine Target. Possible values are
                              "HIGH_ACCURACY", "HIGH_PERFORMANCE", "INVALID".

- wurfl_info                  A string containing information on the parsed
                              wurfl.xml and its full path.

- wurfl_last_load_time        Contains the UNIX timestamp of the last time
                              WURFL has been loaded successfully.

- wurfl_normalized_useragent  The normalized useragent.

- wurfl_useragent_priority    The user agent priority used by WURFL.

Please note that this option is only available when haproxy has been compiled
with USE_WURFL=1.

A char that will be used to separate values in a response header containing
WURFL results. If not set that a comma (',') will be used by default.

Please note that this option is only available when haproxy has been compiled
with USE_WURFL=1.

A list of WURFL patch file paths. Note that patches are loaded during startup
thus before the chroot.

Please note that this option is only available when haproxy has been compiled
with USE_WURFL=1.

Sets the WURFL engine target. You can choose between 'accuracy' or
'performance' targets. In performance mode, desktop web browser detection is
done programmatically without referencing the WURFL data. As a result, most
desktop web browsers are returned as generic_web_browser WURFL ID for
performance. If either performance or accuracy are not defined, performance
mode is enabled by default.

Please note that this option is only available when haproxy has been compiled
with USE_WURFL=1.

Sets the WURFL caching strategy. Here <U> is the Useragent cache size, and
<D> is the internal device cache size. There are three possibilities here :
- "0"     : no cache is used.
- <U>     : the Single LRU cache is used, the size is expressed in elements.
- <U>,<D> : the Double LRU cache is used, both sizes are in elements. This is
            the highest performing option.

Please note that this option is only available when haproxy has been compiled
with USE_WURFL=1.

Tells WURFL if it should prioritize use of the plain user agent ('plain')
over the default sideloaded browser user agent ('sideloaded_browser').

Please note that this option is only available when haproxy has been compiled
with USE_WURFL=1.

In some situations, especially when dealing with low latency on processors
supporting a variable frequency or when running inside virtual machines, each
time the process waits for an I/O using the poller, the processor goes back
to sleep or is offered to another VM for a long time, and it causes
excessively high latencies. This option provides a solution preventing the
processor from sleeping by always using a null timeout on the pollers. This
results in a significant latency reduction (30 to 100 microseconds observed)
at the expense of a risk to overheat the processor. It may even be used with
threads, in which case improperly bound threads may heavily conflict,
resulting in a worse performance and high values for the CPU stolen fields
in "show info" output, indicating which threads are misconfigured. It is
important not to let the process run on the same processor as the network
interrupts when this option is used. It is also better to avoid using it on
multiple CPU threads sharing the same core. This option is disabled by
default. If it has been enabled, it may still be forcibly disabled by
prefixing it with the "no" keyword. It is ignored by the "select" and
"poll" pollers.

By default, haproxy tries to spread the start of health checks across the
smallest health check interval of all the servers in a farm. The principle is
to avoid hammering services running on the same server. But when using large
check intervals (10 seconds or more), the last servers in the farm take some
time before starting to be tested, which can be a problem. This parameter is
used to enforce an upper bound on delay between the first and the last check,
even if the servers' check intervals are larger. When servers run with
shorter intervals, their intervals will be respected though.

Sets the maximum per-process number of concurrent connections to <number>. It
is equivalent to the command-line argument "-n". Proxies will stop accepting
connections when this limit is reached. The "ulimit-n" parameter is
automatically adjusted according to this value. See also "ulimit-n". Note:
the "select" poller cannot reliably use more than 1024 file descriptors on
some platforms. If your platform only supports select and reports "select
FAILED" on startup, you need to reduce maxconn until it works (slightly
below 500 in general). If this value is not set, it will default to the value
set in DEFAULT_MAXCONN at build time (reported in haproxy -vv) if no memory
limit is enforced, or will be computed based on the memory limit, the buffer
size, memory allocated to compression, SSL cache size, and use or not of SSL
and the associated maxsslconn (which can also be automatic).

Sets the maximum per-process number of connections per second to <number>.
Proxies will stop accepting connections when this limit is reached. It can be
used to limit the global capacity regardless of each frontend capacity. It is
important to note that this can only be used as a service protection measure,
as there will not necessarily be a fair share between frontends when the
limit is reached, so it's a good idea to also limit each frontend to some
value close to its expected share. Also, lowering tune.maxaccept can improve
fairness.

Sets the maximum per-process input compression rate to <number> kilobytes
per second. For each session, if the maximum is reached, the compression
level will be decreased during the session. If the maximum is reached at the
beginning of a session, the session will not compress at all. If the maximum
is not reached, the compression level will be increased up to
tune.comp.maxlevel. A value of zero means there is no limit, this is the
default value.

Sets the maximum CPU usage HAProxy can reach before stopping the compression
for new requests or decreasing the compression level of current requests.
It works like 'maxcomprate' but measures CPU usage instead of incoming data
bandwidth. The value is expressed in percent of the CPU used by haproxy. In
case of multiple processes (nbproc > 1), each process manages its individual
usage. A value of 100 disable the limit. The default value is 100. Setting
a lower value will prevent the compression work from slowing the whole
process down and from introducing high latencies.

Sets the maximum per-process number of pipes to <number>. Currently, pipes
are only used by kernel-based tcp splicing. Since a pipe contains two file
descriptors, the "ulimit-n" value will be increased accordingly. The default
value is maxconn/4, which seems to be more than enough for most heavy usages.
The splice code dynamically allocates and releases pipes, and can fall back
to standard copy, so setting this value too low may only impact performance.

Sets the maximum per-process number of sessions per second to <number>.
Proxies will stop accepting connections when this limit is reached. It can be
used to limit the global capacity regardless of each frontend capacity. It is
important to note that this can only be used as a service protection measure,
as there will not necessarily be a fair share between frontends when the
limit is reached, so it's a good idea to also limit each frontend to some
value close to its expected share. Also, lowering tune.maxaccept can improve
fairness.

Sets the maximum per-process number of concurrent SSL connections to
<number>. By default there is no SSL-specific limit, which means that the
global maxconn setting will apply to all connections. Setting this limit
avoids having openssl use too much memory and crash when malloc returns NULL
(since it unfortunately does not reliably check for such conditions). Note
that the limit applies both to incoming and outgoing connections, so one
connection which is deciphered then ciphered accounts for 2 SSL connections.
If this value is not set, but a memory limit is enforced, this value will be
automatically computed based on the memory limit, maxconn,  the buffer size,
memory allocated to compression, SSL cache size, and use of SSL in either
frontends, backends or both. If neither maxconn nor maxsslconn are specified
when there is a memory limit, haproxy will automatically adjust these values
so that 100% of the connections can be made over SSL with no risk, and will
consider the sides where it is enabled (frontend, backend, both).

Sets the maximum per-process number of SSL sessions per second to <number>.
SSL listeners will stop accepting connections when this limit is reached. It
can be used to limit the global SSL CPU usage regardless of each frontend
capacity. It is important to note that this can only be used as a service
protection measure, as there will not necessarily be a fair share between
frontends when the limit is reached, so it's a good idea to also limit each
frontend to some value close to its expected share. It is also important to
note that the sessions are accounted before they enter the SSL stack and not
after, which also protects the stack against bad handshakes. Also, lowering
tune.maxaccept can improve fairness.

Sets the maximum amount of RAM in megabytes per process usable by the zlib.
When the maximum amount is reached, future sessions will not compress as long
as RAM is unavailable. When sets to 0, there is no limit.
The default value is 0. The value is available in bytes on the UNIX socket
with "show info" on the line "MaxZlibMemUsage", the memory used by zlib is
"ZlibMemUsage" in bytes.

Disables the use of the "epoll" event polling system on Linux. It is
equivalent to the command-line argument "-de". The next polling system
used will generally be "poll". See also "nopoll".

Disables the use of the "kqueue" event polling system on BSD. It is
equivalent to the command-line argument "-dk". The next polling system
used will generally be "poll". See also "nopoll".

Disables the use of the "poll" event polling system. It is equivalent to the
command-line argument "-dp". The next polling system used will be "select".
It should never be needed to disable "poll" since it's available on all
platforms supported by HAProxy. See also "nokqueue" and "noepoll".

Disables the use of kernel tcp splicing between sockets on Linux. It is
equivalent to the command line argument "-dS". Data will then be copied
using conventional and more portable recv/send calls. Kernel tcp splicing is
limited to some very recent instances of kernel 2.6. Most versions between
2.6.25 and 2.6.28 are buggy and will forward corrupted data, so they must not
be used. This option makes it easier to globally disable kernel splicing in
case of doubt. See also "option splice-auto", "option splice-request" and
"option splice-response".

Disables the use of getaddrinfo(3) for name resolving. It is equivalent to
the command line argument "-dG". Deprecated gethostbyname(3) will be used.

Disables the use of SO_REUSEPORT - see socket(7). It is equivalent to the
command line argument "-dR".

Enables ('on') or disables ('off') per-task CPU profiling. CPU profiling per
task can be very convenient to report where the time is spent and which
requests have what effect on which other request. It is not enabled by
default as it may consume a little bit extra CPU. This requires a system
supporting the clock_gettime(2) syscall with clock identifiers
CLOCK_MONOTONIC and CLOCK_THREAD_CPUTIME_ID, otherwise the reported time will
be zero. This option may be changed at run time using "set profiling" on the
CLI.

Sometimes it is desirable to avoid sending agent and health checks to
servers at exact intervals, for instance when many logical servers are
located on the same physical server. With the help of this parameter, it
becomes possible to add some randomness in the check interval between 0
and +/- 50%. A value between 2 and 5 seems to show good results. The
default value remains at 0.

Sets the OpenSSL engine to <name>. List of valid values for <name> may be
obtained using the command "openssl engine". This statement may be used
multiple times, it will simply enable multiple crypto engines. Referencing an
unsupported engine will prevent haproxy from starting. Note that many engines
will lead to lower HTTPS performance than pure software with recent
processors. The optional command "algo" sets the default algorithms an ENGINE
will supply using the OPENSSL function ENGINE_set_default_string(). A value
of "ALL" uses the engine for all cryptographic operations. If no list of
algo is specified then the value of "ALL" is used. A comma-separated list
of different algorithms may be specified, including: RSA, DSA, DH, EC, RAND,
CIPHERS, DIGESTS, PKEY, PKEY_CRYPTO, PKEY_ASN1. This is the same format that
openssl configuration file uses:
https://www.openssl.org/docs/man1.0.2/apps/config.html

Adds SSL_MODE_ASYNC mode to the SSL context. This enables asynchronous TLS
I/O operations if asynchronous capable SSL engines are used. The current
implementation supports a maximum of 32 engines. The Openssl ASYNC API
doesn't support moving read/write buffers and is not compliant with
haproxy's buffer management. So the asynchronous mode is disabled on
read/write  operations (it is only enabled during initial and reneg
handshakes).

Sets a hard limit on the number of buffers which may be allocated per process.
The default value is zero which means unlimited. The minimum non-zero value
will always be greater than "tune.buffers.reserve" and should ideally always
be about twice as large. Forcing this value can be particularly useful to
limit the amount of memory a process may take, while retaining a sane
behavior. When this limit is reached, sessions which need a buffer wait for
another one to be released by another session. Since buffers are dynamically
allocated and released, the waiting time is very short and not perceptible
provided that limits remain reasonable. In fact sometimes reducing the limit
may even increase performance by increasing the CPU cache's efficiency. Tests
have shown good results on average HTTP traffic with a limit to 1/10 of the
expected global maxconn setting, which also significantly reduces memory
usage. The memory savings come from the fact that a number of connections
will not allocate 2*tune.bufsize. It is best not to touch this value unless
advised to do so by an haproxy core developer.

Sets the number of buffers which are pre-allocated and reserved for use only
during memory shortage conditions resulting in failed memory allocations. The
minimum value is 2 and is also the default. There is no reason a user would
want to change this value, it's mostly aimed at haproxy core developers.

Sets the buffer size to this size (in bytes). Lower values allow more
sessions to coexist in the same amount of RAM, and higher values allow some
applications with very large cookies to work. The default value is 16384 and
can be changed at build time. It is strongly recommended not to change this
from the default value, as very low values will break some services such as
statistics, and values larger than default size will increase memory usage,
possibly causing the system to run out of memory. At least the global maxconn
parameter should be decreased by the same factor as this one is increased. In
addition, use of HTTP/2 mandates that this value must be 16384 or more. If an
HTTP request is larger than (tune.bufsize - tune.maxrewrite), haproxy will
return HTTP 400 (Bad Request) error. Similarly if an HTTP response is larger
than this size, haproxy will return HTTP 502 (Bad Gateway). Note that the
value set using this parameter will automatically be rounded up to the next
multiple of 8 on 32-bit machines and 16 on 64-bit machines.

Sets the check buffer size to this size (in bytes). Higher values may help
find string or regex patterns in very large pages, though doing so may imply
more memory and CPU usage. The default value is 16384 and can be changed at
build time. It is not recommended to change this value, but to use better
checks whenever possible.

Sets the maximum compression level. The compression level affects CPU
usage during compression. This value affects CPU usage during compression.
Each session using compression initializes the compression algorithm with
this value. The default value is 1.

Sets the HTTP/2 dynamic header table size. It defaults to 4096 bytes and
cannot be larger than 65536 bytes. A larger value may help certain clients
send more compact requests, depending on their capabilities. This amount of
memory is consumed for each HTTP/2 connection. It is recommended not to
change it.

Sets the HTTP/2 initial window size, which is the number of bytes the client
can upload before waiting for an acknowledgment from haproxy. This setting
only affects payload contents (i.e. the body of POST requests), not headers.
The default value is 65535, which roughly allows up to 5 Mbps of upload
bandwidth per client over a network showing a 100 ms ping time, or 500 Mbps
over a 1-ms local network. It can make sense to increase this value to allow
faster uploads, or to reduce it to increase fairness when dealing with many
clients. It doesn't affect resource usage.

Sets the HTTP/2 maximum number of concurrent streams per connection (ie the
number of outstanding requests on a single connection). The default value is
100. A larger one may slightly improve page load time for complex sites when
visited over high latency networks, but increases the amount of resources a
single client may allocate. A value of zero disables the limit so a single
client may create as many streams as allocatable by haproxy. It is highly
recommended not to change this value.

Sets the maximum length of captured cookies. This is the maximum value that
the "capture cookie xxx len yyy" will be allowed to take, and any upper value
will automatically be truncated to this one. It is important not to set too
high a value because all cookie captures still allocate this size whatever
their configured value (they share a same pool). This value is per request
per response, so the memory allocated is twice this value per connection.
When not specified, the limit is set to 63 characters. It is recommended not
to change this value.

Sets the maximum length of request URI in logs. This prevents truncating long
request URIs with valuable query strings in log lines. This is not related
to syslog limits. If you increase this limit, you may also increase the
'log ... len yyy' parameter. Your syslog daemon may also need specific
configuration directives too.
The default value is 1024.

Sets the maximum number of headers in a request. When a request comes with a
number of headers greater than this value (including the first line), it is
rejected with a "400 Bad Request" status code. Similarly, too large responses
are blocked with "502 Bad Gateway". The default value is 101, which is enough
for all usages, considering that the widely deployed Apache server uses the
same limit. It can be useful to push this limit further to temporarily allow
a buggy application to work by the time it gets fixed. The accepted range is
1..32767. Keep in mind that each new header consumes 32bits of memory for
each session, so don't push this limit too high.

Sets the duration after which haproxy will consider that an empty buffer is
probably associated with an idle stream. This is used to optimally adjust
some packet sizes while forwarding large and small data alternatively. The
decision to use splice() or to send large buffers in SSL is modulated by this
parameter. The value is in milliseconds between 0 and 65535. A value of zero
means that haproxy will not try to detect idle streams. The default is 1000,
which seems to correctly detect end user pauses (e.g. read a page before
clicking). There should be not reason for changing this value. Please check
tune.ssl.maxrecord below.

This directive forces the Lua engine to execute a yield each <number> of
instructions executed. This permits interrupting a long script and allows the
HAProxy scheduler to process other tasks like accepting connections or
forwarding traffic. The default value is 10000 instructions. If HAProxy often
executes some Lua code but more responsiveness is required, this value can be
lowered. If the Lua code is quite long and its result is absolutely required
to process the data, the <number> can be increased.

Sets the maximum amount of RAM in megabytes per process usable by Lua. By
default it is zero which means unlimited. It is important to set a limit to
ensure that a bug in a script will not result in the system running out of
memory.

This is the execution timeout for the Lua sessions. This is useful for
preventing infinite loops or spending too much time in Lua. This timeout
counts only the pure Lua runtime. If the Lua does a sleep, the sleep is
not taken in account. The default timeout is 4s.

Purpose is the same as "tune.lua.session-timeout", but this timeout is
dedicated to the tasks. By default, this timeout isn't set because a task may
remain alive during of the lifetime of HAProxy. For example, a task used to
check servers.

This is the execution timeout for the Lua services. This is useful for
preventing infinite loops or spending too much time in Lua. This timeout
counts only the pure Lua runtime. If the Lua does a sleep, the sleep is
not taken in account. The default timeout is 4s.

Sets the maximum number of consecutive connections a process may accept in a
row before switching to other work. In single process mode, higher numbers
give better performance at high connection rates. However in multi-process
modes, keeping a bit of fairness between processes generally is better to
increase performance. This value applies individually to each listener, so
that the number of processes a listener is bound to is taken into account.
This value defaults to 64. In multi-process mode, it is divided by twice
the number of processes the listener is bound to. Setting this value to -1
completely disables the limitation. It should normally not be needed to tweak
this value.

Sets the maximum amount of events that can be processed at once in a call to
the polling system. The default value is adapted to the operating system. It
has been noticed that reducing it below 200 tends to slightly decrease
latency at the expense of network bandwidth, and increasing it above 200
tends to trade latency for slightly increased bandwidth.

Sets the reserved buffer space to this size in bytes. The reserved space is
used for header rewriting or appending. The first reads on sockets will never
fill more than bufsize-maxrewrite. Historically it has defaulted to half of
bufsize, though that does not make much sense since there are rarely large
numbers of headers to add. Setting it too high prevents processing of large
requests or responses. Setting it too low prevents addition of new headers
to already large requests or to POST requests. It is generally wise to set it
to about 1024. It is automatically readjusted to half of bufsize if it is
larger than that. This means you don't have to worry about it when changing
bufsize.

Sets the size of the pattern lookup cache to <number> entries. This is an LRU
cache which reminds previous lookups and their results. It is used by ACLs
and maps on slow pattern lookups, namely the ones using the "sub", "reg",
"dir", "dom", "end", "bin" match methods as well as the case-insensitive
strings. It applies to pattern expressions which means that it will be able
to memorize the result of a lookup among all the patterns specified on a
configuration line (including all those loaded from files). It automatically
invalidates entries which are updated using HTTP actions or on the CLI. The
default cache size is set to 10000 entries, which limits its footprint to
about 5 MB per process/thread on 32-bit systems and 8 MB per process/thread
on 64-bit systems, as caches are thread/process local. There is a very low
risk of collision in this cache, which is in the order of the size of the
cache divided by 2^64. Typically, at 10000 requests per second with the
default cache size of 10000 entries, there's 1% chance that a brute force
attack could cause a single collision after 60 years, or 0.1% after 6 years.
This is considered much lower than the risk of a memory corruption caused by
aging components. If this is not acceptable, the cache can be disabled by
setting this parameter to 0.

Sets the kernel pipe buffer size to this size (in bytes). By default, pipes
are the default size for the system. But sometimes when using TCP splicing,
it can improve performance to increase pipe sizes, especially if it is
suspected that pipes are not filled and that many calls to splice() are
performed. This has an impact on the kernel's memory footprint, so this must
not be changed if impacts are not understood.

Forces the kernel socket receive buffer size on the client or the server side
to the specified value in bytes. This value applies to all TCP/HTTP frontends
and backends. It should normally never be set, and the default size (0) lets
the kernel autotune this value depending on the amount of available memory.
However it can sometimes help to set it to very low values (e.g. 4096) in
order to save kernel memory by preventing it from buffering too large amounts
of received data. Lower values will significantly increase CPU usage though.

HAProxy uses some hints to detect that a short read indicates the end of the
socket buffers. One of them is that a read returns more than <recv_enough>
bytes, which defaults to 10136 (7 segments of 1448 each). This default value
may be changed by this setting to better deal with workloads involving lots
of short messages such as telnet or SSH sessions.

Sets the maxinum amount of task that can be processed at once when running
tasks. The default value is 200. Increasing it may incur latency when
dealing with I/Os, making it too small can incur extra overhead.

Forces the kernel socket send buffer size on the client or the server side to
the specified value in bytes. This value applies to all TCP/HTTP frontends
and backends. It should normally never be set, and the default size (0) lets
the kernel autotune this value depending on the amount of available memory.
However it can sometimes help to set it to very low values (e.g. 4096) in
order to save kernel memory by preventing it from buffering too large amounts
of received data. Lower values will significantly increase CPU usage though.
Another use case is to prevent write timeouts with extremely slow clients due
to the kernel waiting for a large part of the buffer to be read before
notifying haproxy again.

Sets the size of the global SSL session cache, in a number of blocks. A block
is large enough to contain an encoded session without peer certificate.
An encoded session with peer certificate is stored in multiple blocks
depending on the size of the peer certificate. A block uses approximately
200 bytes of memory. The default value may be forced at build time, otherwise
defaults to 20000. When the cache is full, the most idle entries are purged
and reassigned. Higher values reduce the occurrence of such a purge, hence
the number of CPU-intensive SSL handshakes by ensuring that all users keep
their session as long as possible. All entries are pre-allocated upon startup
and are shared between all processes if "nbproc" is greater than 1. Setting
this value to 0 disables the SSL session cache.

This option disables SSL session cache sharing between all processes. It
should normally not be used since it will force many renegotiations due to
clients hitting a random process. But it may be required on some operating
systems where none of the SSL cache synchronization method may be used. In
this case, adding a first layer of hash-based load balancing before the SSL
layer might limit the impact of the lack of session sharing.

Sets how long a cached SSL session may remain valid. This time is expressed
in seconds and defaults to 300 (5 min). It is important to understand that it
does not guarantee that sessions will last that long, because if the cache is
full, the longest idle sessions will be purged despite their configured
lifetime. The real usefulness of this setting is to prevent sessions from
being used for too long.

Sets the maximum amount of bytes passed to SSL_write() at a time. Default
value 0 means there is no limit. Over SSL/TLS, the client can decipher the
data only once it has received a full record. With large records, it means
that clients might have to download up to 16kB of data before starting to
process them. Limiting the value can improve page load times on browsers
located over high latency or low bandwidth networks. It is suggested to find
optimal values which fit into 1 or 2 TCP segments (generally 1448 bytes over
Ethernet with TCP timestamps enabled, or 1460 when timestamps are disabled),
keeping in mind that SSL/TLS add some overhead. Typical values of 1419 and
2859 gave good results during tests. Use "strace -e trace=write" to find the
best value. HAProxy will automatically switch to this setting after an idle
stream has been detected (see tune.idletimer above).

Sets the maximum size of the Diffie-Hellman parameters used for generating
the ephemeral/temporary Diffie-Hellman key in case of DHE key exchange. The
final size will try to match the size of the server's RSA (or DSA) key (e.g,
a 2048 bits temporary DH key for a 2048 bits RSA key), but will not exceed
this maximum value. Default value if 1024. Only 1024 or higher values are
allowed. Higher values will increase the CPU load, and values greater than
1024 bits are not supported by Java 7 and earlier clients. This value is not
used if static Diffie-Hellman parameters are supplied either directly
in the certificate file or by using the ssl-dh-param-file parameter.

Sets the size of the cache used to store generated certificates to <number>
entries. This is a LRU cache. Because generating a SSL certificate
dynamically is expensive, they are cached. The default cache size is set to
1000 entries.

Sets the maximum size of the buffer used for capturing client-hello cipher
list. If the value is 0 (default value) the capture is disabled, otherwise
a buffer is allocated for each SSL/TLS connection.

These five tunes help to manage the maximum amount of memory used by the
variables system. "global" limits the overall amount of memory available for
all scopes. "proc" limits the memory for the process scope, "sess" limits the
memory for the session scope, "txn" for the transaction scope, and "reqres"
limits the memory for each request or response processing.
Memory accounting is hierarchical, meaning more coarse grained limits include
the finer grained ones: "proc" includes "sess", "sess" includes "txn", and
"txn" includes "reqres".

For example, when "tune.vars.sess-max-size" is limited to 100,
"tune.vars.txn-max-size" and "tune.vars.reqres-max-size" cannot exceed
100 either. If we create a variable "txn.var" that contains 100 bytes,
all available space is consumed.
Notice that exceeding the limits at runtime will not result in an error
message, but values might be cut off or corrupted. So make sure to accurately
plan for the amount of space needed to store all your variables.

Sets the memLevel parameter in zlib initialization for each session. It
defines how much memory should be allocated for the internal compression
state. A value of 1 uses minimum memory but is slow and reduces compression
ratio, a value of 9 uses maximum memory for optimal speed. Can be a value
between 1 and 9. The default value is 8.

Sets the window size (the size of the history buffer) as a parameter of the
zlib initialization for each session. Larger values of this parameter result
in better compression at the expense of memory usage. Can be a value between
8 and 15. The default value is 15.

Enables debug mode which dumps to stdout all exchanges, and disables forking
into background. It is the equivalent of the command-line argument "-d". It
should never be used in a production configuration since it may prevent full
system startup.

Do not display any message during startup. It is equivalent to the command-
line argument "-q".

It is possible to control access to frontend/backend/listen sections or to
http stats by allowing only authenticated and authorized users. To do this,
it is required to create at least one userlist and to define users.

Creates new userlist with name <listname>. Many independent userlists can be
used to store authentication & authorization data for independent customers.

Adds group <groupname> to the current userlist. It is also possible to
attach users to this group by using a comma separated list of names
proceeded by "users" keyword.

Adds user <username> to the current userlist. Both secure (encrypted) and
insecure (unencrypted) passwords can be used. Encrypted passwords are
evaluated using the crypt(3) function, so depending on the system's
capabilities, different algorithms are supported. For example, modern Glibc
based Linux systems support MD5, SHA-256, SHA-512, and, of course, the
classic DES-based method of encrypting passwords.

Attention: Be aware that using encrypted passwords might cause significantly
increased CPU usage, depending on the number of requests, and the algorithm
used. For any of the hashed variants, the password for each request must
be processed through the chosen algorithm, before it can be compared to the
value specified in the config file. Most current algorithms are deliberately
designed to be expensive to compute to achieve resistance against brute
force attacks. They do not simply salt/hash the clear text password once,
but thousands of times. This can quickly become a major factor in haproxy's
overall CPU consumption!

userlist L1
  group G1 users tiger,scott
  group G2 users xdb,scott

  user tiger password $6$k6y3o.eP$JlKBx9za9667qe4(...)xHSwRv6J.C0/D7cV91
  user scott insecure-password elgato
  user xdb insecure-password hello

userlist L2
  group G1
  group G2

  user tiger password $6$k6y3o.eP$JlKBx(...)xHSwRv6J.C0/D7cV91 groups G1
  user scott insecure-password elgato groups G1,G2
  user xdb insecure-password hello groups G2

Please note that both lists are functionally identical.

It is possible to propagate entries of any data-types in stick-tables between
several haproxy instances over TCP connections in a multi-master fashion. Each
instance pushes its local updates and insertions to remote peers. The pushed
values overwrite remote ones without aggregation. Interrupted exchanges are
automatically detected and recovered from the last known point.
In addition, during a soft restart, the old process connects to the new one
using such a TCP connection to push all its entries before the new process
tries to connect to other peers. That ensures very fast replication during a
reload, it typically takes a fraction of a second even for large tables.
Note that Server IDs are used to identify servers remotely, so it is important
that configurations look similar or at least that the same IDs are forced on
each server on all participants.

Creates a new peer list with name <peersect>. It is an independent section,
which is referenced by one or more stick-tables.

Disables a peers section. It disables both listening and any synchronization
related to this section. This is provided to disable synchronization of stick
tables without having to comment out all "peers" references.

This re-enables a disabled peers section which was previously disabled.

Defines a peer inside a peers section.
If <peername> is set to the local peer name (by default hostname, or forced
using "-L" command line option), haproxy will listen for incoming remote peer
connection on <ip>:<port>. Otherwise, <ip>:<port> defines where to connect to
to join the remote peer, and <peername> is used at the protocol level to
identify and validate the remote peer on the server side.

During a soft restart, local peer <ip>:<port> is used by the old instance to
connect the new one and initiate a complete replication (teaching process).

It is strongly recommended to have the exact same peers declaration on all
peers and to only rely on the "-L" command line argument to change the local
peer name. This makes it easier to maintain coherent configuration files
across all peers.

You may want to reference some environment variables in the address
parameter, see section 2.3 about environment variables.

peers mypeers
    peer haproxy1 192.168.0.1:1024
    peer haproxy2 192.168.0.2:1024
    peer haproxy3 10.2.0.1:1024

backend mybackend
    mode tcp
    balance roundrobin
    stick-table type ip size 20k peers mypeers
    stick on src

    server srv1 192.168.0.30:80
    server srv2 192.168.0.31:80

It is possible to send email alerts when the state of servers changes.
If configured email alerts are sent to each mailer that is configured
in a mailers section. Email is sent to mailers using SMTP.

Creates a new mailer list with the name <mailersect>. It is an
independent section which is referenced by one or more proxies.

Defines a mailer inside a mailers section.

mailers mymailers
    mailer smtp1 192.168.0.1:587
    mailer smtp2 192.168.0.2:587

backend mybackend
    mode tcp
    balance roundrobin

    email-alert mailers mymailers
    email-alert from [email protected]
    email-alert to [email protected]

    server srv1 192.168.0.30:80
    server srv2 192.168.0.31:80

Defines the time available for a mail/connection to be made and send to
the mail-server. If not defined the default value is 10 seconds. To allow
for at least two SYN-ACK packets to be send during initial TCP handshake it
is advised to keep this value above 4 seconds.

mailers mymailers
    timeout mail 20s
    mailer smtp1 192.168.0.1:587

Proxy configuration can be located in a set of sections :
 - defaults [<name>]
 - frontend <name>
 - backend  <name>
 - listen   <name>

A "defaults" section sets default parameters for all other sections following
its declaration. Those default parameters are reset by the next "defaults"
section. See below for the list of parameters which can be set in a "defaults"
section. The name is optional but its use is encouraged for better readability.

A "frontend" section describes a set of listening sockets accepting client
connections.

A "backend" section describes a set of servers to which the proxy will connect
to forward incoming connections.

A "listen" section defines a complete proxy with its frontend and backend
parts combined in one section. It is generally useful for TCP-only traffic.

All proxy names must be formed from upper and lower case letters, digits,
'-' (dash), '_' (underscore) , '.' (dot) and ':' (colon). ACL names are
case-sensitive, which means that "www" and "WWW" are two different proxies.

Historically, all proxy names could overlap, it just caused troubles in the
logs. Since the introduction of content switching, it is mandatory that two
proxies with overlapping capabilities (frontend/backend) have different names.
However, it is still permitted that a frontend and a backend share the same
name, as this configuration seems to be commonly encountered.

Right now, two major proxy modes are supported : "tcp", also known as layer 4,
and "http", also known as layer 7. In layer 4 mode, HAProxy simply forwards
bidirectional traffic between two sides. In layer 7 mode, HAProxy analyzes the
protocol, and can interact with it by allowing, blocking, switching, adding,
modifying, or removing arbitrary contents in requests or responses, based on
arbitrary criteria.

In HTTP mode, the processing applied to requests and responses flowing over
a connection depends in the combination of the frontend's HTTP options and
the backend's. HAProxy supports 4 connection modes :

  - KAL : keep alive ("option http-keep-alive") which is the default mode : all
    requests and responses are processed, and connections remain open but idle
    between responses and new requests.

  - TUN: tunnel ("option http-tunnel") : this was the default mode for versions
    1.0 to 1.5-dev21 : only the first request and response are processed, and
    everything else is forwarded with no analysis at all. This mode should not
    be used as it creates lots of trouble with logging and HTTP processing.
    And because it cannot work in HTTP/2, this option is deprecated and it is
    only supported on legacy HTTP frontends. In HTX, it is ignored and a
    warning is emitted during HAProxy startup.

  - SCL: server close ("option http-server-close") : the server-facing
    connection is closed after the end of the response is received, but the
    client-facing connection remains open.

  - CLO: close ("option httpclose"): the connection is closed after the end of
    the response and "Connection: close" appended in both directions.

The effective mode that will be applied to a connection passing through a
frontend and a backend can be determined by both proxy modes according to the
following matrix, but in short, the modes are symmetric, keep-alive is the
weakest option and close is the strongest.

                   Backend mode

                | KAL | SCL | CLO
            ----+-----+-----+----
            KAL | KAL | SCL | CLO
            ----+-----+-----+----
            TUN | TUN | SCL | CLO
 Frontend   ----+-----+-----+----
   mode     SCL | SCL | SCL | CLO
            ----+-----+-----+----
            CLO | CLO | CLO | CLO

The following list of keywords is supported. Most of them may only be used in a
limited set of section types. Some of them are marked as "deprecated" because
they are inherited from an old syntax which may be confusing or functionally
limited, and there are new recommended keywords to replace them. Keywords
marked with "(*)" can be optionally inverted using the "no" prefix, e.g. "no
option contstats". This makes sense when the option has been enabled by default
and must be disabled for a specific instance. Such options may also be prefixed
with "default" in order to restore default settings regardless of what has been
specified in a previous "defaults" section.

keyword	defaults	frontend	listen	backend
acl
appsession
backlog
balance
bind
bind-process
(deprecated)block
capture cookie
capture request header
capture response header
(deprecated)clitimeout
compression
(deprecated)contimeout
cookie
declare capture
default-server
default_backend
description
disabled
dispatch
keyword	defaults	frontend	listen	backend
email-alert from
email-alert level
email-alert mailers
email-alert myhostname
email-alert to
enabled
errorfile
errorloc
errorloc302
errorloc303
force-persist
filter
fullconn
grace
hash-type
http-check disable-on-404
http-check expect
http-check send-state
http-request
http-response
keyword	defaults	frontend	listen	backend
http-reuse
http-send-name-header
id
ignore-persist
load-server-state-from-file
(*)log
log-format
log-format-sd
log-tag
max-keep-alive-queue
maxconn
mode
monitor fail
monitor-net
monitor-uri
(*)option abortonclose
(*)option accept-invalid-http-request
(*)option accept-invalid-http-response
(*)option allbackups
(*)option checkcache
keyword	defaults	frontend	listen	backend
(*)option clitcpka
(*)option contstats
(*)option dontlog-normal
(*)option dontlognull
(deprecated)(*)option forceclose
option forwardfor
(*)option http-buffer-request
(*)option http-ignore-probes
(*)option http-keep-alive
(*)option http-no-delay
(*)option http-pretend-keepalive
(*)option http-server-close
(deprecated)(*)option http-tunnel
(*)option http-use-proxy-header
(*)option http-use-htx
option httpchk
(*)option httpclose
option httplog
(*)option http_proxy
(*)option independent-streams
keyword	defaults	frontend	listen	backend
option ldap-check
option external-check
(*)option log-health-checks
(*)option log-separate-errors
(*)option logasap
option mysql-check
(*)option nolinger
option originalto
(*)option persist
option pgsql-check
(*)option prefer-last-server
(*)option redispatch
option redis-check
option smtpchk
(*)option socket-stats
(*)option splice-auto
(*)option splice-request
(*)option splice-response
option spop-check
(*)option srvtcpka
keyword	defaults	frontend	listen	backend
option ssl-hello-chk
option tcp-check
(*)option tcp-smart-accept
(*)option tcp-smart-connect
option tcpka
option tcplog
(*)option transparent
external-check command
external-check path
persist rdp-cookie
rate-limit sessions
redirect
(deprecated)redisp
(deprecated)redispatch
reqadd
reqallow
reqdel
reqdeny
reqiallow
reqidel
keyword	defaults	frontend	listen	backend
reqideny
reqipass
reqirep
reqitarpit
reqpass
reqrep
reqtarpit
retries
rspadd
rspdel
rspdeny
rspidel
rspideny
rspirep
rsprep
server
server-state-file-name
server-template
source
(deprecated)srvtimeout
keyword	defaults	frontend	listen	backend
stats admin
stats auth
stats enable
stats hide-version
stats http-request
stats realm
stats refresh
stats scope
stats show-desc
stats show-legends
stats show-node
stats uri
stick match
stick on
stick store-request
stick store-response
stick-table
tcp-check connect
tcp-check expect
tcp-check send
keyword	defaults	frontend	listen	backend
tcp-check send-binary
tcp-request connection
tcp-request content
tcp-request inspect-delay
tcp-request session
tcp-response content
tcp-response inspect-delay
timeout check
timeout client
timeout client-fin
(deprecated)timeout clitimeout
timeout connect
(deprecated)timeout contimeout
timeout http-keep-alive
timeout http-request
timeout queue
timeout server
timeout server-fin
(deprecated)timeout srvtimeout
timeout tarpit
keyword	defaults	frontend	listen	backend
timeout tunnel
(deprecated)transparent
unique-id-format
unique-id-header
use_backend
use-server

This section provides a description of each keyword and its usage.

Declare or complete an access list.

acl invalid_src  src          0.0.0.0/7 224.0.0.0/3
acl invalid_src  src_port     0:1023
acl local_dst    hdr(host) -i localhost

See section 7 about ACL usage.

Define session stickiness on an existing application cookie.

<cookie>   this is the name of the cookie used by the application and which
           HAProxy will have to learn for each new session.

<length>   this is the max number of characters that will be memorized and
           checked in each cookie value.

<holdtime> this is the time after which the cookie will be removed from
           memory if unused. If no unit is specified, this time is in
           milliseconds.

request-learn
           If this option is specified, then haproxy will be able to learn
           the cookie found in the request in case the server does not
           specify any in response. This is typically what happens with
           PHPSESSID cookies, or when haproxy's session expires before
           the application's session and the correct server is selected.
           It is recommended to specify this option to improve reliability.

prefix     When this option is specified, haproxy will match on the cookie
           prefix (or URL parameter prefix). The appsession value is the
           data following this prefix.

           Example :
           appsession ASPSESSIONID len 64 timeout 3h prefix

           This will match the cookie ASPSESSIONIDXXX=XXXX,
           the appsession value will be XXX=XXXX.

mode       This option allows to change the URL parser mode.
           2 modes are currently supported :
           - path-parameters :
             The parser looks for the appsession in the path parameters
             part (each parameter is separated by a semi-colon), which is
             convenient for JSESSIONID for example.
             This is the default mode if the option is not set.
           - query-string :
             In this mode, the parser will look for the appsession in the
             query string.

As of version 1.6, appsessions was removed. It is more flexible and more
convenient to use stick-tables instead, and stick-tables support multi-master
replication and data conservation across reloads, which appsessions did not.

Give hints to the system about the approximate listen backlog desired size

<conns>   is the number of pending connections. Depending on the operating
          system, it may represent the number of already acknowledged
          connections, of non-acknowledged ones, or both.

In order to protect against SYN flood attacks, one solution is to increase
the system's SYN backlog size. Depending on the system, sometimes it is just
tunable via a system parameter, sometimes it is not adjustable at all, and
sometimes the system relies on hints given by the application at the time of
the listen() syscall. By default, HAProxy passes the frontend's maxconn value
to the listen() syscall. On systems which can make use of this value, it can
sometimes be useful to be able to specify a different value, hence this
backlog parameter.

On Linux 2.4, the parameter is ignored by the system. On Linux 2.6, it is
used as a hint and the system accepts up to the smallest greater power of
two, and never more than some limits (usually 32768).

Define the load balancing algorithm to be used in a backend.

<algorithm> is the algorithm used to select a server when doing load
            balancing. This only applies when no persistence information
            is available, or when a connection is redispatched to another
            server. <algorithm> may be one of the following :

  roundrobin  Each server is used in turns, according to their weights.
              This is the smoothest and fairest algorithm when the server's
              processing time remains equally distributed. This algorithm
              is dynamic, which means that server weights may be adjusted
              on the fly for slow starts for instance. It is limited by
              design to 4095 active servers per backend. Note that in some
              large farms, when a server becomes up after having been down
              for a very short time, it may sometimes take a few hundreds
              requests for it to be re-integrated into the farm and start
              receiving traffic. This is normal, though very rare. It is
              indicated here in case you would have the chance to observe
              it, so that you don't worry.

  static-rr   Each server is used in turns, according to their weights.
              This algorithm is as similar to roundrobin except that it is
              static, which means that changing a server's weight on the
              fly will have no effect. On the other hand, it has no design
              limitation on the number of servers, and when a server goes
              up, it is always immediately reintroduced into the farm, once
              the full map is recomputed. It also uses slightly less CPU to
              run (around -1%).

  leastconn   The server with the lowest number of connections receives the
              connection. Round-robin is performed within groups of servers
              of the same load to ensure that all servers will be used. Use
              of this algorithm is recommended where very long sessions are
              expected, such as LDAP, SQL, TSE, etc... but is not very well
              suited for protocols using short sessions such as HTTP. This
              algorithm is dynamic, which means that server weights may be
              adjusted on the fly for slow starts for instance.

  first       The first server with available connection slots receives the
              connection. The servers are chosen from the lowest numeric
              identifier to the highest (see server parameter "id"), which
              defaults to the server's position in the farm. Once a server
              reaches its maxconn value, the next server is used. It does
              not make sense to use this algorithm without setting maxconn.
              The purpose of this algorithm is to always use the smallest
              number of servers so that extra servers can be powered off
              during non-intensive hours. This algorithm ignores the server
              weight, and brings more benefit to long session such as RDP
              or IMAP than HTTP, though it can be useful there too. In
              order to use this algorithm efficiently, it is recommended
              that a cloud controller regularly checks server usage to turn
              them off when unused, and regularly checks backend queue to
              turn new servers on when the queue inflates. Alternatively,
              using "http-check send-state" may inform servers on the load.

  source      The source IP address is hashed and divided by the total
              weight of the running servers to designate which server will
              receive the request. This ensures that the same client IP
              address will always reach the same server as long as no
              server goes down or up. If the hash result changes due to the
              number of running servers changing, many clients will be
              directed to a different server. This algorithm is generally
              used in TCP mode where no cookie may be inserted. It may also
              be used on the Internet to provide a best-effort stickiness
              to clients which refuse session cookies. This algorithm is
              static by default, which means that changing a server's
              weight on the fly will have no effect, but this can be
              changed using "hash-type".

  uri         This algorithm hashes either the left part of the URI (before
              the question mark) or the whole URI (if the "whole" parameter
              is present) and divides the hash value by the total weight of
              the running servers. The result designates which server will
              receive the request. This ensures that the same URI will
              always be directed to the same server as long as no server
              goes up or down. This is used with proxy caches and
              anti-virus proxies in order to maximize the cache hit rate.
              Note that this algorithm may only be used in an HTTP backend.
              This algorithm is static by default, which means that
              changing a server's weight on the fly will have no effect,
              but this can be changed using "hash-type".

              This algorithm supports two optional parameters "len" and
              "depth", both followed by a positive integer number. These
              options may be helpful when it is needed to balance servers
              based on the beginning of the URI only. The "len" parameter
              indicates that the algorithm should only consider that many
              characters at the beginning of the URI to compute the hash.
              Note that having "len" set to 1 rarely makes sense since most
              URIs start with a leading "/".

              The "depth" parameter indicates the maximum directory depth
              to be used to compute the hash. One level is counted for each
              slash in the request. If both parameters are specified, the
              evaluation stops when either is reached.

  url_param   The URL parameter specified in argument will be looked up in
              the query string of each HTTP GET request.

              If the modifier "check_post" is used, then an HTTP POST
              request entity will be searched for the parameter argument,
              when it is not found in a query string after a question mark
              ('?') in the URL. The message body will only start to be
              analyzed once either the advertised amount of data has been
              received or the request buffer is full. In the unlikely event
              that chunked encoding is used, only the first chunk is
              scanned. Parameter values separated by a chunk boundary, may
              be randomly balanced if at all. This keyword used to support
              an optional <max_wait> parameter which is now ignored.

              If the parameter is found followed by an equal sign ('=') and
              a value, then the value is hashed and divided by the total
              weight of the running servers. The result designates which
              server will receive the request.

              This is used to track user identifiers in requests and ensure
              that a same user ID will always be sent to the same server as
              long as no server goes up or down. If no value is found or if
              the parameter is not found, then a round robin algorithm is
              applied. Note that this algorithm may only be used in an HTTP
              backend. This algorithm is static by default, which means
              that changing a server's weight on the fly will have no
              effect, but this can be changed using "hash-type".

  hdr(<name>) The HTTP header <name> will be looked up in each HTTP
              request. Just as with the equivalent ACL 'hdr()' function,
              the header name in parenthesis is not case sensitive. If the
              header is absent or if it does not contain any value, the
              roundrobin algorithm is applied instead.

              An optional 'use_domain_only' parameter is available, for
              reducing the hash algorithm to the main domain part with some
              specific headers such as 'Host'. For instance, in the Host
              value "haproxy.1wt.eu", only "1wt" will be considered.

              This algorithm is static by default, which means that
              changing a server's weight on the fly will have no effect,
              but this can be changed using "hash-type".

  random      A random number will be used as the key for the consistent
              hashing function. This means that the servers' weights are
              respected, dynamic weight changes immediately take effect, as
              well as new server additions. Random load balancing can be
              useful with large farms or when servers are frequently added
              or removed. The hash-balance-factor directive can be used to
              further improve fairness of the load balancing, especially
              in situations where servers show highly variable response
              times.

  rdp-cookie
  rdp-cookie(<name>)
              The RDP cookie <name> (or "mstshash" if omitted) will be
              looked up and hashed for each incoming TCP request. Just as
              with the equivalent ACL 'req_rdp_cookie()' function, the name
              is not case-sensitive. This mechanism is useful as a degraded
              persistence mode, as it makes it possible to always send the
              same user (or the same session ID) to the same server. If the
              cookie is not found, the normal roundrobin algorithm is
              used instead.

              Note that for this to work, the frontend must ensure that an
              RDP cookie is already present in the request buffer. For this
              you must use 'tcp-request content accept' rule combined with
              a 'req_rdp_cookie_cnt' ACL.

              This algorithm is static by default, which means that
              changing a server's weight on the fly will have no effect,
              but this can be changed using "hash-type".

              See also the rdp_cookie pattern fetch function.

<arguments> is an optional list of arguments which may be needed by some
            algorithms. Right now, only "url_param" and "uri" support an
            optional argument.

The load balancing algorithm of a backend is set to roundrobin when no other
algorithm, mode nor option have been set. The algorithm may only be set once
for each backend.

With authentication schemes that require the same connection like NTLM, URI
based alghoritms must not be used, as they would cause subsequent requests
to be routed to different backend servers, breaking the invalid assumptions
NTLM relies on.

balance roundrobin
balance url_param userid
balance url_param session_id check_post 64
balance hdr(User-Agent)
balance hdr(host)
balance hdr(Host) use_domain_only

Note: the following caveats and limitations on using the "check_post"
extension with "url_param" must be considered :

  - all POST requests are eligible for consideration, because there is no way
    to determine if the parameters will be found in the body or entity which
    may contain binary data. Therefore another method may be required to
    restrict consideration of POST requests that have no URL parameters in
    the body. (see acl reqideny http_end)

  - using a <max_wait> value larger than the request buffer size does not
    make sense and is useless. The buffer size is set at build time, and
    defaults to 16 kB.

  - Content-Encoding is not supported, the parameter search will probably
    fail; and load balancing will fall back to Round Robin.

  - Expect: 100-continue is not supported, load balancing will fall back to
    Round Robin.

  - Transfer-Encoding (RFC7230 3.3.1) is only supported in the first chunk.
    If the entire parameter value is not present in the first chunk, the
    selection of server is undefined (actually, defined by how little
    actually appeared in the first chunk).

  - This feature does not support generation of a 100, 411 or 501 response.

  - In some cases, requesting "check_post" MAY attempt to scan the entire
    contents of a message body. Scanning normally terminates when linear
    white space or control characters are found, indicating the end of what
    might be a URL parameter list. This is probably not a concern with SGML
    type message bodies.

Define one or several listening addresses and/or ports in a frontend.

<address>     is optional and can be a host name, an IPv4 address, an IPv6
              address, or '*'. It designates the address the frontend will
              listen on. If unset, all IPv4 addresses of the system will be
              listened on. The same will apply for '*' or the system's
              special address "0.0.0.0". The IPv6 equivalent is '::'.
              Optionally, an address family prefix may be used before the
              address to force the family regardless of the address format,
              which can be useful to specify a path to a unix socket with
              no slash ('/'). Currently supported prefixes are :
                - 'ipv4@'  -> address is always IPv4
                - 'ipv6@'  -> address is always IPv6
                - 'unix@'  -> address is a path to a local unix socket
                - 'abns@'  -> address is in abstract namespace (Linux only).
                  Note: since abstract sockets are not "rebindable", they
                        do not cope well with multi-process mode during
                        soft-restart, so it is better to avoid them if
                        nbproc is greater than 1. The effect is that if the
                        new process fails to start, only one of the old ones
                        will be able to rebind to the socket.
                - 'fd@<n>' -> use file descriptor <n> inherited from the
                  parent. The fd must be bound and may or may not already
                  be listening.
                - 'sockpair@<n>'-> like fd@ but you must use the fd of a
                  connected unix socket or of a socketpair. The bind waits
                  to receive a FD over the unix socket and uses it as if it
                  was the FD of an accept(). Should be used carefully.
              You may want to reference some environment variables in the
              address parameter, see section 2.3 about environment
              variables.

<port_range>  is either a unique TCP port, or a port range for which the
              proxy will accept connections for the IP address specified
              above. The port is mandatory for TCP listeners. Note that in
              the case of an IPv6 address, the port is always the number
              after the last colon (':'). A range can either be :
               - a numerical port (ex: '80')
               - a dash-delimited ports range explicitly stating the lower
                 and upper bounds (ex: '2000-2100') which are included in
                 the range.

              Particular care must be taken against port ranges, because
              every <address:port> couple consumes one socket (= a file
              descriptor), so it's easy to consume lots of descriptors
              with a simple range, and to run out of sockets. Also, each
              <address:port> couple must be used only once among all
              instances running on a same system. Please note that binding
              to ports lower than 1024 generally require particular
              privileges to start the program, which are independent of
              the 'uid' parameter.

<path>        is a UNIX socket path beginning with a slash ('/'). This is
              alternative to the TCP listening port. HAProxy will then
              receive UNIX connections on the socket located at this place.
              The path must begin with a slash and by default is absolute.
              It can be relative to the prefix defined by "unix-bind" in
              the global section. Note that the total length of the prefix
              followed by the socket path cannot exceed some system limits
              for UNIX sockets, which commonly are set to 107 characters.

<param*>      is a list of parameters common to all sockets declared on the
              same line. These numerous parameters depend on OS and build
              options and have a complete section dedicated to them. Please
              refer to section 5 to for more details.

It is possible to specify a list of address:port combinations delimited by
commas. The frontend will then listen on all of these addresses. There is no
fixed limit to the number of addresses and ports which can be listened on in
a frontend, as well as there is no limit to the number of "bind" statements
in a frontend.

listen http_proxy
    bind :80,:443
    bind 10.0.0.1:10080,10.0.0.1:10443
    bind /var/run/ssl-frontend.sock user root mode 600 accept-proxy

listen http_https_proxy
    bind :80
    bind :443 ssl crt /etc/haproxy/site.pem

listen http_https_proxy_explicit
    bind ipv6@:80
    bind ipv4@public_ssl:443 ssl crt /etc/haproxy/site.pem
    bind [email protected] user root mode 600 accept-proxy

listen external_bind_app1
    bind "fd@${FD_APP1}"

Note: regarding Linux's abstract namespace sockets, HAProxy uses the whole
      sun_path length is used for the address length. Some other programs
      such as socat use the string length only by default. Pass the option
      ",unix-tightsocklen=0" to any abstract socket definition in socat to
      make it compatible with HAProxy's.

Limit visibility of an instance to a certain set of processes numbers.

all           All process will see this instance. This is the default. It
              may be used to override a default value.

odd           This instance will be enabled on processes 1,3,5,...63. This
              option may be combined with other numbers.

even          This instance will be enabled on processes 2,4,6,...64. This
              option may be combined with other numbers. Do not use it
              with less than 2 processes otherwise some instances might be
              missing from all processes.

process_num   The instance will be enabled on this process number or range,
              whose values must all be between 1 and 32 or 64 depending on
              the machine's word size. Ranges can be partially defined. The
              higher bound can be omitted. In such case, it is replaced by
              the corresponding maximum value. If a proxy is bound to
              process numbers greater than the configured global.nbproc, it
              will either be forced to process #1 if a single process was
              specified, or to all processes otherwise.

This keyword limits binding of certain instances to certain processes. This
is useful in order not to have too many processes listening to the same
ports. For instance, on a dual-core machine, it might make sense to set
'nbproc 2' in the global section, then distributes the listeners among 'odd'
and 'even' instances.

At the moment, it is not possible to reference more than 32 or 64 processes
using this keyword, but this should be more than enough for most setups.
Please note that 'all' really means all processes regardless of the machine's
word size, and is not limited to the first 32 or 64.

Each "bind" line may further be limited to a subset of the proxy's processes,
please consult the "process" bind keyword in section 5.1.

When a frontend has no explicit "bind-process" line, it tries to bind to all
the processes referenced by its "bind" lines. That means that frontends can
easily adapt to their listeners' processes.

If some backends are referenced by frontends bound to other processes, the
backend automatically inherits the frontend's processes.

listen app_ip1
    bind 10.0.0.1:80
    bind-process odd

listen app_ip2
    bind 10.0.0.2:80
    bind-process even

listen management
    bind 10.0.0.3:80
    bind-process 1 2 3 4

listen management
    bind 10.0.0.4:80
    bind-process 1-4

Block a layer 7 request if/unless a condition is matched

The HTTP request will be blocked very early in the layer 7 processing
if/unless <condition> is matched. A 403 error will be returned if the request
is blocked. The condition has to reference ACLs (see section 7). This is
typically used to deny access to certain sensitive resources if some
conditions are met or not met. There is no fixed limit to the number of
"block" statements per instance. To block connections at layer 4 (without
sending a 403 error) see "tcp-request connection reject" and
"tcp-request content reject" rules.

This form is deprecated, do not use it in any new configuration, use the new
"http-request deny" instead.

acl invalid_src  src          0.0.0.0/7 224.0.0.0/3
acl invalid_src  src_port     0:1023
acl local_dst    hdr(host) -i localhost
# block is deprecated. Use http-request deny instead:
#block if invalid_src || local_dst
http-request deny if invalid_src || local_dst

Capture and log a cookie in the request and in the response.

<name>    is the beginning of the name of the cookie to capture. In order
          to match the exact name, simply suffix the name with an equal
          sign ('='). The full name will appear in the logs, which is
          useful with application servers which adjust both the cookie name
          and value (e.g. ASPSESSIONXXX).

<length>  is the maximum number of characters to report in the logs, which
          include the cookie name, the equal sign and the value, all in the
          standard "name=value" form. The string will be truncated on the
          right if it exceeds <length>.

Only the first cookie is captured. Both the "cookie" request headers and the
"set-cookie" response headers are monitored. This is particularly useful to
check for application bugs causing session crossing or stealing between
users, because generally the user's cookies can only change on a login page.

When the cookie was not presented by the client, the associated log column
will report "-". When a request does not cause a cookie to be assigned by the
server, a "-" is reported in the response column.

The capture is performed in the frontend only because it is necessary that
the log format does not change for a given frontend depending on the
backends. This may change in the future. Note that there can be only one
"capture cookie" statement in a frontend. The maximum capture length is set
by the global "tune.http.cookielen" setting and defaults to 63 characters. It
is not possible to specify a capture in a "defaults" section.

capture cookie ASPSESSION len 32

Capture and log the last occurrence of the specified request header.

<name>    is the name of the header to capture. The header names are not
          case-sensitive, but it is a common practice to write them as they
          appear in the requests, with the first letter of each word in
          upper case. The header name will not appear in the logs, only the
          value is reported, but the position in the logs is respected.

<length>  is the maximum number of characters to extract from the value and
          report in the logs. The string will be truncated on the right if
          it exceeds <length>.

The complete value of the last occurrence of the header is captured. The
value will be added to the logs between braces ('{}'). If multiple headers
are captured, they will be delimited by a vertical bar ('|') and will appear
in the same order they were declared in the configuration. Non-existent
headers will be logged just as an empty string. Common uses for request
header captures include the "Host" field in virtual hosting environments, the
"Content-length" when uploads are supported, "User-agent" to quickly
differentiate between real users and robots, and "X-Forwarded-For" in proxied
environments to find where the request came from.

Note that when capturing headers such as "User-agent", some spaces may be
logged, making the log analysis more difficult. Thus be careful about what
you log if you know your log parser is not smart enough to rely on the
braces.

There is no limit to the number of captured request headers nor to their
length, though it is wise to keep them low to limit memory usage per session.
In order to keep log format consistent for a same frontend, header captures
can only be declared in a frontend. It is not possible to specify a capture
in a "defaults" section.

capture request header Host len 15
capture request header X-Forwarded-For len 15
capture request header Referer len 15

Capture and log the last occurrence of the specified response header.

<name>    is the name of the header to capture. The header names are not
          case-sensitive, but it is a common practice to write them as they
          appear in the response, with the first letter of each word in
          upper case. The header name will not appear in the logs, only the
          value is reported, but the position in the logs is respected.

<length>  is the maximum number of characters to extract from the value and
          report in the logs. The string will be truncated on the right if
          it exceeds <length>.

The complete value of the last occurrence of the header is captured. The
result will be added to the logs between braces ('{}') after the captured
request headers. If multiple headers are captured, they will be delimited by
a vertical bar ('|') and will appear in the same order they were declared in
the configuration. Non-existent headers will be logged just as an empty
string. Common uses for response header captures include the "Content-length"
header which indicates how many bytes are expected to be returned, the
"Location" header to track redirections.

There is no limit to the number of captured response headers nor to their
length, though it is wise to keep them low to limit memory usage per session.
In order to keep log format consistent for a same frontend, header captures
can only be declared in a frontend. It is not possible to specify a capture
in a "defaults" section.

capture response header Content-length len 9
capture response header Location len 15

Set the maximum inactivity time on the client side.

<timeout> is the timeout value is specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

The inactivity timeout applies when the client is expected to acknowledge or
send data. In HTTP mode, this timeout is particularly important to consider
during the first phase, when the client sends the request, and during the
response while it is reading data sent by the server. The value is specified
in milliseconds by default, but can be in any other unit if the number is
suffixed by the unit, as specified at the top of this document. In TCP mode
(and to a lesser extent, in HTTP mode), it is highly recommended that the
client timeout remains equal to the server timeout in order to avoid complex
situations to debug. It is a good practice to cover one or several TCP packet
losses by specifying timeouts that are slightly above multiples of 3 seconds
(e.g. 4 or 5 seconds).

This parameter is specific to frontends, but can be specified once for all in
"defaults" sections. This is in fact one of the easiest solutions not to
forget about it. An unspecified timeout results in an infinite timeout, which
is not recommended. Such a usage is accepted and works but reports a warning
during startup because it may results in accumulation of expired sessions in
the system if the system's timeouts are not configured either.

This parameter is provided for compatibility but is currently deprecated.
Please use "timeout client" instead.

Enable HTTP compression.

algo     is followed by the list of supported compression algorithms.
type     is followed by the list of MIME types that will be compressed.
offload  makes haproxy work as a compression offloader only (see notes).

The currently supported algorithms are :
  identity     this is mostly for debugging, and it was useful for developing
               the compression feature. Identity does not apply any change on
               data.

  gzip         applies gzip compression. This setting is only available when
               support for zlib or libslz was built in.

  deflate      same as "gzip", but with deflate algorithm and zlib format.
               Note that this algorithm has ambiguous support on many
               browsers and no support at all from recent ones. It is
               strongly recommended not to use it for anything else than
               experimentation. This setting is only available when support
               for zlib or libslz was built in.

  raw-deflate  same as "deflate" without the zlib wrapper, and used as an
               alternative when the browser wants "deflate". All major
               browsers understand it and despite violating the standards,
               it is known to work better than "deflate", at least on MSIE
               and some versions of Safari. Do not use it in conjunction
               with "deflate", use either one or the other since both react
               to the same Accept-Encoding token. This setting is only
               available when support for zlib or libslz was built in.

Compression will be activated depending on the Accept-Encoding request
header. With identity, it does not take care of that header.
If backend servers support HTTP compression, these directives
will be no-op: haproxy will see the compressed response and will not
compress again. If backend servers do not support HTTP compression and
there is Accept-Encoding header in request, haproxy will compress the
matching response.

The "offload" setting makes haproxy remove the Accept-Encoding header to
prevent backend servers from compressing responses. It is strongly
recommended not to do this because this means that all the compression work
will be done on the single point where haproxy is located. However in some
deployment scenarios, haproxy may be installed in front of a buggy gateway
with broken HTTP compression implementation which can't be turned off.
In that case haproxy can be used to prevent that gateway from emitting
invalid payloads. In this case, simply removing the header in the
configuration does not work because it applies before the header is parsed,
so that prevents haproxy from compressing. The "offload" setting should
then be used for such scenarios. Note: for now, the "offload" setting is
ignored when set in a defaults section.

Compression is disabled when:
  * the request does not advertise a supported compression algorithm in the
    "Accept-Encoding" header
  * the response message is not HTTP/1.1
  * HTTP status code is not one of 200, 201, 202, or 203
  * response contain neither a "Content-Length" header nor a
    "Transfer-Encoding" whose last value is "chunked"
  * response contains a "Content-Type" header whose first value starts with
    "multipart"
  * the response contains the "no-transform" value in the "Cache-control"
    header
  * User-Agent matches "Mozilla/4" unless it is MSIE 6 with XP SP2, or MSIE 7
    and later
  * The response contains a "Content-Encoding" header, indicating that the
    response is already compressed (see compression offload)
  * The response contains an invalid "ETag" header or multiple ETag headers

Note: The compression does not emit the Warning header.

compression algo gzip
compression type text/html text/plain

Set the maximum time to wait for a connection attempt to a server to succeed.

<timeout> is the timeout value is specified in milliseconds by default, but
          can be in any other unit if the number is suffixed by the unit,
          as explained at the top of this document.

If the server is located on the same LAN as haproxy, the connection should be
immediate (less than a few milliseconds). Anyway, it is a good practice to
cover one or several TCP packet losses by specifying timeouts that are
slightly above multiples of 3 seconds (e.g. 4 or 5 seconds). By default, the
connect timeout also presets the queue timeout to the same value if this one
has not been specified. Historically, the contimeout was also used to set the
tarpit timeout in a listen section, which is not possible in a pure frontend.

This parameter is specific to backends, but can be specified once for all in
"defaults" sections. This is in fact one of the easiest solutions not to
forget about it. An unspecified timeout results in an infinite timeout, which
is not recommended. Such a usage is accepted and works but reports a warning
during startup because it may results in accumulation of failed sessions in
the system if the system's timeouts are not configured either.

This parameter is provided for backwards compatibility but is currently
deprecated. Please use "timeout connect", "timeout queue" or "timeout tarpit"
instead.

Enable cookie-based persistence in a backend.

<name>    is the name of the cookie which will be monitored, modified or
          inserted in order to bring persistence. This cookie is sent to
          the client via a "Set-Cookie" header in the response, and is
          brought back by the client in a "Cookie" header in all requests.
          Special care should be taken to choose a name which does not
          conflict with any likely application cookie. Also, if the same
          backends are subject to be used by the same clients (e.g.
          HTTP/HTTPS), care should be taken to use different cookie names
          between all backends if persistence between them is not desired.

rewrite   This keyword indicates that the cookie will be provided by the
          server and that haproxy will have to modify its value to set the
          server's identifier in it. This mode is handy when the management
          of complex combinations of "Set-cookie" and "Cache-control"
          headers is left to the application. The application can then
          decide whether or not it is appropriate to emit a persistence
          cookie. Since all responses should be monitored, this mode
          doesn't work in HTTP tunnel mode. Unless the application
          behavior is very complex and/or broken, it is advised not to
          start with this mode for new deployments. This keyword is
          incompatible with "insert" and "prefix".

insert    This keyword indicates that the persistence cookie will have to
          be inserted by haproxy in server responses if the client did not

          already have a cookie that would have permitted it to access this
          server. When used without the "preserve" option, if the server
          emits a cookie with the same name, it will be removed before
          processing. For this reason, this mode can be used to upgrade
          existing configurations running in the "rewrite" mode. The cookie
          will only be a session cookie and will not be stored on the
          client's disk. By default, unless the "indirect" option is added,
          the server will see the cookies emitted by the client. Due to
          caching effects, it is generally wise to add the "nocache" or
          "postonly" keywords (see below). The "insert" keyword is not
          compatible with "rewrite" and "prefix".

prefix    This keyword indicates that instead of relying on a dedicated
          cookie for the persistence, an existing one will be completed.
          This may be needed in some specific environments where the client
          does not support more than one single cookie and the application
          already needs it. In this case, whenever the server sets a cookie
          named <name>, it will be prefixed with the server's identifier
          and a delimiter. The prefix will be removed from all client
          requests so that the server still finds the cookie it emitted.
          Since all requests and responses are subject to being modified,
          this mode doesn't work with tunnel mode. The "prefix" keyword is
          not compatible with "rewrite" and "insert". Note: it is highly
          recommended not to use "indirect" with "prefix", otherwise server
          cookie updates would not be sent to clients.

indirect  When this option is specified, no cookie will be emitted to a
          client which already has a valid one for the server which has
          processed the request. If the server sets such a cookie itself,
          it will be removed, unless the "preserve" option is also set. In
          "insert" mode, this will additionally remove cookies from the
          requests transmitted to the server, making the persistence
          mechanism totally transparent from an application point of view.
          Note: it is highly recommended not to use "indirect" with
          "prefix", otherwise server cookie updates would not be sent to
          clients.

nocache   This option is recommended in conjunction with the insert mode
          when there is a cache between the client and HAProxy, as it
          ensures that a cacheable response will be tagged non-cacheable if
          a cookie needs to be inserted. This is important because if all
          persistence cookies are added on a cacheable home page for
          instance, then all customers will then fetch the page from an
          outer cache and will all share the same persistence cookie,
          leading to one server receiving much more traffic than others.
          See also the "insert" and "postonly" options.

postonly  This option ensures that cookie insertion will only be performed
          on responses to POST requests. It is an alternative to the
          "nocache" option, because POST responses are not cacheable, so
          this ensures that the persistence cookie will never get cached.
          Since most sites do not need any sort of persistence before the
          first POST which generally is a login request, this is a very
          efficient method to optimize caching without risking to find a
          persistence cookie in the cache.
          See also the "insert" and "nocache" options.

preserve  This option may only be used with "insert" and/or "indirect". It
          allows the server to emit the persistence cookie itself. In this
          case, if a cookie is found in the response, haproxy will leave it
          untouched. This is useful in order to end persistence after a
          logout request for instance. For this, the server just has to
          emit a cookie with an invalid value (e.g. empty) or with a date in
          the past. By combining this mechanism with the "disable-on-404"
          check option, it is possible to perform a completely graceful
          shutdown because users will definitely leave the server after
          they logout.

httponly  This option tells haproxy to add an "HttpOnly" cookie attribute
          when a cookie is inserted. This attribute is used so that a
          user agent doesn't share the cookie with non-HTTP components.
          Please check RFC6265 for more information on this attribute.

secure    This option tells haproxy to add a "Secure" cookie attribute when
          a cookie is inserted. This attribute is used so that a user agent
          never emits this cookie over non-secure channels, which means
          that a cookie learned with this flag will be presented only over
          SSL/TLS connections. Please check RFC6265 for more information on
          this attribute.

domain    This option allows to specify the domain at which a cookie is
          inserted. It requires exactly one parameter: a valid domain
          name. If the domain begins with a dot, the browser is allowed to
          use it for any host ending with that name. It is also possible to
          specify several domain names by invoking this option multiple
          times. Some browsers might have small limits on the number of
          domains, so be careful when doing that. For the record, sending
          10 domains to MSIE 6 or Firefox 2 works as expected.

maxidle   This option allows inserted cookies to be ignored after some idle
          time. It only works with insert-mode cookies. When a cookie is
          sent to the client, the date this cookie was emitted is sent too.
          Upon further presentations of this cookie, if the date is older
          than the delay indicated by the parameter (in seconds), it will
          be ignored. Otherwise, it will be refreshed if needed when the
          response is sent to the client. This is particularly useful to
          prevent users who never close their browsers from remaining for
          too long on the same server (e.g. after a farm size change). When
          this option is set and a cookie has no date, it is always
          accepted, but gets refreshed in the response. This maintains the
          ability for admins to access their sites. Cookies that have a
          date in the future further than 24 hours are ignored. Doing so
          lets admins fix timezone issues without risking kicking users off
          the site.

maxlife   This option allows inserted cookies to be ignored after some life
          time, whether they're in use or not. It only works with insert
          mode cookies. When a cookie is first sent to the client, the date
          this cookie was emitted is sent too. Upon further presentations
          of this cookie, if the date is older than the delay indicated by
          the parameter (in seconds), it will be ignored. If the cookie in
          the request has no date, it is accepted and a date will be set.
          Cookies that have a date in the future further than 24 hours are
          ignored. Doing so lets admins fix timezone issues without risking
          kicking users off the site. Contrary to maxidle, this value is
          not refreshed, only the first visit date counts. Both maxidle and
          maxlife may be used at the time. This is particularly useful to
          prevent users who never close their browsers from remaining for
          too long on the same server (e.g. after a farm size change). This
          is stronger than the maxidle method in that it forces a
          redispatch after some absolute delay.

dynamic   Activate dynamic cookies. When used, a session cookie is
          dynamically created for each server, based on the IP and port
          of the server, and a secret key, specified in the
          "dynamic-cookie-key" backend directive.
          The cookie will be regenerated each time the IP address change,
          and is only generated for IPv4/IPv6.

attr      This option tells haproxy to add an extra attribute when a
          cookie is inserted. The attribute value can contain any
          characters except control ones or ";". This option may be
          repeated.

There can be only one persistence cookie per HTTP backend, and it can be
declared in a defaults section. The value of the cookie will be the value
indicated after the "cookie" keyword in a "server" statement. If no cookie
is declared for a given server, the cookie is not set.

cookie JSESSIONID prefix
cookie SRV insert indirect nocache
cookie SRV insert postonly indirect
cookie SRV insert indirect nocache maxidle 30m maxlife 8h

Declares a capture slot.

<length> is the length allowed for the capture.

This declaration is only available in the frontend or listen section, but the
reserved slot can be used in the backends. The "request" keyword allocates a
capture slot for use in the request, and "response" allocates a capture slot
for use in the response.

Change default options for a server in a backend

<param*>  is a list of parameters for this server. The "default-server"
          keyword accepts an important number of options and has a complete
          section dedicated to it. Please refer to section 5 for more
          details.

default-server inter 1000 weight 13

Specify the backend to use when no "use_backend" rule has been matched.

<backend> is the name of the backend to use.

When doing content-switching between frontend and backends using the
"use_backend" keyword, it is often useful to indicate which backend will be
used when no rule has matched. It generally is the dynamic backend which
will catch all undetermined requests.

use_backend     dynamic  if  url_dyn
use_backend     static   if  url_css url_img extension_img
default_backend dynamic

Describe a listen, frontend or backend.

Allows to add a sentence to describe the related object in the HAProxy HTML
stats page. The description will be printed on the right of the object name
it describes.
No need to backslash spaces in the <string> arguments.

Disable a proxy, frontend or backend.

The "disabled" keyword is used to disable an instance, mainly in order to
liberate a listening port or to temporarily disable a service. The instance
will still be created and its configuration will be checked, but it will be
created in the "stopped" state and will appear as such in the statistics. It
will not receive any traffic nor will it send any health-checks or logs. It
is possible to disable many instances at once by adding the "disabled"
keyword in a "defaults" section.

Set a default server address

<address> is the IPv4 address of the default server. Alternatively, a
          resolvable hostname is supported, but this name will be resolved
          during start-up.

<ports>   is a mandatory port specification. All connections will be sent
          to this port, and it is not permitted to use port offsets as is
          possible with normal servers.

The "dispatch" keyword designates a default server for use when no other
server can take the connection. In the past it was used to forward non
persistent connections to an auxiliary load balancer. Due to its simple
syntax, it has also been used for simple TCP relays. It is recommended not to
use it for more clarity, and to use the "server" directive instead.

Set the dynamic cookie secret key for a backend.

When dynamic cookies are enabled (see the "dynamic" directive for cookie),
a dynamic cookie is created for each server (unless one is explicitly
specified on the "server" line), using a hash of the IP address of the
server, the TCP port, and the secret key.
That way, we can ensure session persistence across multiple load-balancers,
even if servers are dynamically added or removed.

Enable a proxy, frontend or backend.

The "enabled" keyword is used to explicitly enable an instance, when the
defaults has been set to "disabled". This is very rarely used.

Return a file contents instead of errors generated by HAProxy

<code>    is the HTTP status code. Currently, HAProxy is capable of
          generating codes 200, 400, 403, 405, 408, 425, 429, 500, 502,
          503, and 504.

<file>    designates a file containing the full HTTP response. It is
          recommended to follow the common practice of appending ".http" to
          the filename so that people do not confuse the response with HTML
          error pages, and to use absolute paths, since files are read
          before any chroot is performed.

It is important to understand that this keyword is not meant to rewrite
errors returned by the server, but errors detected and returned by HAProxy.
This is why the list of supported errors is limited to a small set.

Code 200 is emitted in response to requests matching a "monitor-uri" rule.

The files are returned verbatim on the TCP socket. This allows any trick such
as redirections to another URL or site, as well as tricks to clean cookies,
force enable or disable caching, etc... The package provides default error
files returning the same contents as default errors.

The files should not exceed the configured buffer size (BUFSIZE), which
generally is 8 or 16 kB, otherwise they will be truncated. It is also wise
not to put any reference to local contents (e.g. images) in order to avoid
loops between the client and HAProxy when all servers are down, causing an
error to be returned instead of an image. For better HTTP compliance, it is
recommended that all header lines end with CR-LF and not LF alone.

The files are read at the same time as the configuration and kept in memory.
For this reason, the errors continue to be returned even when the process is
chrooted, and no file change is considered while the process is running. A
simple method for developing those files consists in associating them to the
403 status code and interrogating a blocked URL.

errorfile 400 /etc/haproxy/errorfiles/400badreq.http
errorfile 408 /dev/null  # work around Chrome pre-connect bug
errorfile 403 /etc/haproxy/errorfiles/403forbid.http
errorfile 503 /etc/haproxy/errorfiles/503sorry.http

Return an HTTP redirection to a URL instead of errors generated by HAProxy

<code>    is the HTTP status code. Currently, HAProxy is capable of
          generating codes 200, 400, 403, 405, 408, 425, 429, 500, 502,
          503, and 504.

<url>     it is the exact contents of the "Location" header. It may contain
          either a relative URI to an error page hosted on the same site,
          or an absolute URI designating an error page on another site.
          Special care should be given to relative URIs to avoid redirect
          loops if the URI itself may generate the same error (e.g. 500).

It is important to understand that this keyword is not meant to rewrite
errors returned by the server, but errors detected and returned by HAProxy.
This is why the list of supported errors is limited to a small set.

Code 200 is emitted in response to requests matching a "monitor-uri" rule.

Note that both keyword return the HTTP 302 status code, which tells the
client to fetch the designated URL using the same HTTP method. This can be
quite problematic in case of non-GET methods such as POST, because the URL
sent to the client might not be allowed for something other than GET. To
work around this problem, please use "errorloc303" which send the HTTP 303
status code, indicating to the client that the URL must be fetched with a GET
request.

Return an HTTP redirection to a URL instead of errors generated by HAProxy

<code>    is the HTTP status code. Currently, HAProxy is capable of
          generating codes 200, 400, 403, 405, 408, 425, 429, 500, 502,
          503, and 504.

<url>     it is the exact contents of the "Location" header. It may contain
          either a relative URI to an error page hosted on the same site,
          or an absolute URI designating an error page on another site.
          Special care should be given to relative URIs to avoid redirect
          loops if the URI itself may generate the same error (e.g. 500).

It is important to understand that this keyword is not meant to rewrite
errors returned by the server, but errors detected and returned by HAProxy.
This is why the list of supported errors is limited to a small set.

Code 200 is emitted in response to requests matching a "monitor-uri" rule.

Note that both keyword return the HTTP 303 status code, which tells the
client to fetch the designated URL using the same HTTP GET method. This
solves the usual problems associated with "errorloc" and the 302 code. It is
possible that some very old browsers designed before HTTP/1.1 do not support
it, but no such problem has been reported till now.

Declare the from email address to be used in both the envelope and header
of email alerts. This is the address that email alerts are sent from.

<emailaddr> is the from email address to use when sending email alerts

Also requires "email-alert mailers" and "email-alert to" to be set
and if so sending email alerts is enabled for the proxy.

Declare the maximum log level of messages for which email alerts will be
sent. This acts as a filter on the sending of email alerts.

<level> One of the 8 syslog levels:
          emerg alert crit err warning notice info  debug
        The above syslog levels are ordered from lowest to highest.

By default level is alert

Also requires "email-alert from", "email-alert mailers" and
"email-alert to" to be set and if so sending email alerts is enabled
for the proxy.

Alerts are sent when :

* An un-paused server is marked as down and <level> is alert or lower
* A paused server is marked as down and <level> is notice or lower
* A server is marked as up or enters the drain state and <level>
  is notice or lower
* "option log-health-checks" is enabled, <level> is info or lower,
   and a health check status update occurs

Declare the mailers to be used when sending email alerts

<mailersect> is the name of the mailers section to send email alerts.

Also requires "email-alert from" and "email-alert to" to be set
and if so sending email alerts is enabled for the proxy.

Declare the to hostname address to be used when communicating with
mailers.

<hostname> is the hostname to use when communicating with mailers

By default the systems hostname is used.

Also requires "email-alert from", "email-alert mailers" and
"email-alert to" to be set and if so sending email alerts is enabled
for the proxy.

Declare both the recipient address in the envelope and to address in the
header of email alerts. This is the address that email alerts are sent to.

<emailaddr> is the to email address to use when sending email alerts

Also requires "email-alert mailers" and "email-alert to" to be set
and if so sending email alerts is enabled for the proxy.

Declare a condition to force persistence on down servers

By default, requests are not dispatched to down servers. It is possible to
force this using "option persist", but it is unconditional and redispatches
to a valid server if "option redispatch" is set. That leaves with very little
possibilities to force some requests to reach a server which is artificially
marked down for maintenance operations.

The "force-persist" statement allows one to declare various ACL-based
conditions which, when met, will cause a request to ignore the down status of
a server and still try to connect to it. That makes it possible to start a
server, still replying an error to the health checks, and run a specially
configured browser to test the service. Among the handy methods, one could
use a specific source IP address, or a specific cookie. The cookie also has
the advantage that it can easily be added/removed on the browser from a test
page. Once the service is validated, it is then possible to open the service
to the world by returning a valid response to health checks.

The forced persistence is enabled when an "if" condition is met, or unless an
"unless" condition is met. The final redispatch is always disabled when this
is used.

Add the filter <name> in the filter list attached to the proxy.

<name>     is the name of the filter. Officially supported filters are
           referenced in section 9.

<param*>   is a list of parameters accepted by the filter <name>. The
           parsing of these parameters are the responsibility of the
           filter. Please refer to the documentation of the corresponding
           filter (section 9) for all details on the supported parameters.

Multiple occurrences of the filter line can be used for the same proxy. The
same filter can be referenced many times if needed.

listen
  bind *:80

  filter trace name BEFORE-HTTP-COMP
  filter compression
  filter trace name AFTER-HTTP-COMP

  compression algo gzip
  compression offload

  server srv1 192.168.0.1:80

Specify at what backend load the servers will reach their maxconn

<conns>   is the number of connections on the backend which will make the
          servers use the maximal number of connections.

When a server has a "maxconn" parameter specified, it means that its number
of concurrent connections will never go higher. Additionally, if it has a
"minconn" parameter, it indicates a dynamic limit following the backend's
load. The server will then always accept at least <minconn> connections,
never more than <maxconn>, and the limit will be on the ramp between both
values when the backend has less than <conns> concurrent connections. This
makes it possible to limit the load on the servers during normal loads, but
push it further for important loads without overloading the servers during
exceptional loads.

Since it's hard to get this value right, haproxy automatically sets it to
10% of the sum of the maxconns of all frontends that may branch to this
backend (based on "use_backend" and "default_backend" rules). That way it's
safe to leave it unset. However, "use_backend" involving dynamic names are
not counted since there is no way to know if they could match or not.

# The servers will accept between 100 and 1000 concurrent connections each
# and the maximum of 1000 will be reached when the backend reaches 10000
# connections.
backend dynamic
   fullconn   10000
   server     srv1   dyn1:80 minconn 100 maxconn 1000
   server     srv2   dyn2:80 minconn 100 maxconn 1000

Maintain a proxy operational for some time after a soft stop

<time>    is the time (by default in milliseconds) for which the instance
          will remain operational with the frontend sockets still listening
          when a soft-stop is received via the SIGUSR1 signal.

This may be used to ensure that the services disappear in a certain order.
This was designed so that frontends which are dedicated to monitoring by an
external equipment fail immediately while other ones remain up for the time
needed by the equipment to detect the failure.

Note that currently, there is very little benefit in using this parameter,
and it may in fact complicate the soft-reconfiguration process more than
simplify it.

Specify the balancing factor for bounded-load consistent hashing

<factor> is the control for the maximum number of concurrent requests to
         send to a server, expressed as a percentage of the average number
         of concurrent requests across all of the active servers.

Specifying a "hash-balance-factor" for a server with "hash-type consistent"
enables an algorithm that prevents any one server from getting too many
requests at once, even if some hash buckets receive many more requests than
others. Setting <factor> to 0 (the default) disables the feature. Otherwise,
<factor> is a percentage greater than 100. For example, if <factor> is 150,
then no server will be allowed to have a load more than 1.5 times the average.
If server weights are used, they will be respected.

If the first-choice server is disqualified, the algorithm will choose another
server based on the request hash, until a server with additional capacity is
found. A higher <factor> allows more imbalance between the servers, while a
lower <factor> means that more servers will be checked on average, affecting
performance. Reasonable values are from 125 to 200.

This setting is also used by "balance random" which internally relies on the
consistent hashing mechanism.

Specify a method to use for mapping hashes to servers

<method> is the method used to select a server from the hash computed by
         the <function> :

  map-based   the hash table is a static array containing all alive servers.
              The hashes will be very smooth, will consider weights, but
              will be static in that weight changes while a server is up
              will be ignored. This means that there will be no slow start.
              Also, since a server is selected by its position in the array,
              most mappings are changed when the server count changes. This
              means that when a server goes up or down, or when a server is
              added to a farm, most connections will be redistributed to
              different servers. This can be inconvenient with caches for
              instance.

  consistent  the hash table is a tree filled with many occurrences of each
              server. The hash key is looked up in the tree and the closest
              server is chosen. This hash is dynamic, it supports changing
              weights while the servers are up, so it is compatible with the
              slow start feature. It has the advantage that when a server
              goes up or down, only its associations are moved. When a
              server is added to the farm, only a few part of the mappings
              are redistributed, making it an ideal method for caches.
              However, due to its principle, the distribution will never be
              very smooth and it may sometimes be necessary to adjust a
              server's weight or its ID to get a more balanced distribution.
              In order to get the same distribution on multiple load
              balancers, it is important that all servers have the exact
              same IDs. Note: consistent hash uses sdbm and avalanche if no
              hash function is specified.

<function> is the hash function to be used :

   sdbm   this function was created initially for sdbm (a public-domain
          reimplementation of ndbm) database library. It was found to do
          well in scrambling bits, causing better distribution of the keys
          and fewer splits. It also happens to be a good general hashing
          function with good distribution, unless the total server weight
          is a multiple of 64, in which case applying the avalanche
          modifier may help.

   djb2   this function was first proposed by Dan Bernstein many years ago
          on comp.lang.c. Studies have shown that for certain workload this
          function provides a better distribution than sdbm. It generally
          works well with text-based inputs though it can perform extremely
          poorly with numeric-only input or when the total server weight is
          a multiple of 33, unless the avalanche modifier is also used.

   wt6    this function was designed for haproxy while testing other
          functions in the past. It is not as smooth as the other ones, but
          is much less sensible to the input data set or to the number of
          servers. It can make sense as an alternative to sdbm+avalanche or
          djb2+avalanche for consistent hashing or when hashing on numeric
          data such as a source IP address or a visitor identifier in a URL
          parameter.

   crc32  this is the most common CRC32 implementation as used in Ethernet,
          gzip, PNG, etc. It is slower than the other ones but may provide
          a better distribution or less predictable results especially when
          used on strings.

<modifier> indicates an optional method applied after hashing the key :

   avalanche   This directive indicates that the result from the hash
               function above should not be used in its raw form but that
               a 4-byte full avalanche hash must be applied first. The
               purpose of this step is to mix the resulting bits from the
               previous hash in order to avoid any undesired effect when
               the input contains some limited values or when the number of
               servers is a multiple of one of the hash's components (64
               for SDBM, 33 for DJB2). Enabling avalanche tends to make the
               result less predictable, but it's also not as smooth as when
               using the original function. Some testing might be needed
               with some workloads. This hash is one of the many proposed
               by Bob Jenkins.

The default hash type is "map-based" and is recommended for most usages. The
default function is "sdbm", the selection of a function should be based on
the range of the values being hashed.

Enable a maintenance mode upon HTTP/404 response to health-checks

When this option is set, a server which returns an HTTP code 404 will be
excluded from further load-balancing, but will still receive persistent
connections. This provides a very convenient method for Web administrators
to perform a graceful shutdown of their servers. It is also important to note
that a server which is detected as failed while it was in this mode will not
generate an alert, just a notice. If the server responds 2xx or 3xx again, it
will immediately be reinserted into the farm. The status on the stats page
reports "NOLB" for a server in this mode. It is important to note that this
option only works in conjunction with the "httpchk" option. If this option
is used with "http-check expect", then it has precedence over it so that 404
responses will still be considered as soft-stop.

Make HTTP health checks consider response contents or specific status codes

<match>   is a keyword indicating how to look for a specific pattern in the
          response. The keyword may be one of "status", "rstatus",
          "string", or "rstring". The keyword may be preceded by an
          exclamation mark ("!") to negate the match. Spaces are allowed
          between the exclamation mark and the keyword. See below for more
          details on the supported keywords.

<pattern> is the pattern to look for. It may be a string or a regular
          expression. If the pattern contains spaces, they must be escaped
          with the usual backslash ('\').

By default, "option httpchk" considers that response statuses 2xx and 3xx
are valid, and that others are invalid. When "http-check expect" is used,
it defines what is considered valid or invalid. Only one "http-check"
statement is supported in a backend. If a server fails to respond or times
out, the check obviously fails. The available matches are :

  status <string> : test the exact string match for the HTTP status code.
                    A health check response will be considered valid if the
                    response's status code is exactly this string. If the
                    "status" keyword is prefixed with "!", then the response
                    will be considered invalid if the status code matches.

  rstatus <regex> : test a regular expression for the HTTP status code.
                    A health check response will be considered valid if the
                    response's status code matches the expression. If the
                    "rstatus" keyword is prefixed with "!", then the response
                    will be considered invalid if the status code matches.
                    This is mostly used to check for multiple codes.

  string <string> : test the exact string match in the HTTP response body.
                    A health check response will be considered valid if the
                    response's body contains this exact string. If the
                    "string" keyword is prefixed with "!", then the response
                    will be considered invalid if the body contains this
                    string. This can be used to look for a mandatory word at
                    the end of a dynamic page, or to detect a failure when a
                    specific error appears on the check page (e.g. a stack
                    trace).

  rstring <regex> : test a regular expression on the HTTP response body.
                    A health check response will be considered valid if the
                    response's body matches this expression. If the "rstring"
                    keyword is prefixed with "!", then the response will be
                    considered invalid if the body matches the expression.
                    This can be used to look for a mandatory word at the end
                    of a dynamic page, or to detect a failure when a specific
                    error appears on the check page (e.g. a stack trace).

It is important to note that the responses will be limited to a certain size
defined by the global "tune.chksize" option, which defaults to 16384 bytes.
Thus, too large responses may not contain the mandatory pattern when using
"string" or "rstring". If a large response is absolutely required, it is
possible to change the default max size by setting the global variable.
However, it is worth keeping in mind that parsing very large responses can
waste some CPU cycles, especially when regular expressions are used, and that
it is always better to focus the checks on smaller resources.

Also "http-check expect" doesn't support HTTP keep-alive. Keep in mind that it
will automatically append a "Connection: close" header, meaning that this
header should not be present in the request provided by "option httpchk".

Last, if "http-check expect" is combined with "http-check disable-on-404",
then this last one has precedence when the server responds with 404.

# only accept status 200 as valid
http-check expect status 200

# consider SQL errors as errors
http-check expect ! string SQL\ Error

# consider status 5xx only as errors
http-check expect ! rstatus ^5

# check that we have a correct hexadecimal tag before /html
http-check expect rstring <!--tag:[0-9a-f]*--></html>

Add a possible list of headers and/or a body to the request sent during HTTP
health checks.

hdr <name> <value>   adds the HTTP header field whose name is specified in
                     <name> and whose value is defined by <value> to the
                     request sent during HTTP health checks.

body <string>        add the body defined by <string> to the request sent
                     sent during HTTP health checks. If defined, the
                     "Content-Length" header is thus automatically added
                     to the request.

In addition to the request line defined by the "option httpchk" directive,
this one is the valid way to add some headers and optionally a body to the
request sent during HTTP health checks. If a body is defined, the associate
"Content-Length" header is automatically added. The old trick consisting to
add headers after the version string on the "option httpchk" line is now
deprecated. Note also the "Connection: close" header is still added if a
"http-check expect" direcive is defined independently of this directive, just
like the state header if the directive "http-check send-state" is defined.

Enable emission of a state header with HTTP health checks

When this option is set, haproxy will systematically send a special header
"X-Haproxy-Server-State" with a list of parameters indicating to each server
how they are seen by haproxy. This can be used for instance when a server is
manipulated without access to haproxy and the operator needs to know whether
haproxy still sees it up or not, or if the server is the last one in a farm.

The header is composed of fields delimited by semi-colons, the first of which
is a word ("UP", "DOWN", "NOLB"), possibly followed by a number of valid
checks on the total number before transition, just as appears in the stats
interface. Next headers are in the form "<variable>=<value>", indicating in
no specific order some values available in the stats interface :
  - a variable "address", containing the address of the backend server.
    This corresponds to the <address> field in the server declaration. For
    unix domain sockets, it will read "unix".

  - a variable "port", containing the port of the backend server. This
    corresponds to the <port> field in the server declaration. For unix
    domain sockets, it will read "unix".

  - a variable "name", containing the name of the backend followed by a slash
    ("/") then the name of the server. This can be used when a server is
    checked in multiple backends.

  - a variable "node" containing the name of the haproxy node, as set in the
    global "node" variable, otherwise the system's hostname if unspecified.

  - a variable "weight" indicating the weight of the server, a slash ("/")
    and the total weight of the farm (just counting usable servers). This
    helps to know if other servers are available to handle the load when this
    one fails.

  - a variable "scur" indicating the current number of concurrent connections
    on the server, followed by a slash ("/") then the total number of
    connections on all servers of the same backend.

  - a variable "qcur" indicating the current number of requests in the
    server's queue.

Example of a header received by the application server :
  >>>  X-Haproxy-Server-State: UP 2/3; name=bck/srv2; node=lb1; weight=1/2; \
         scur=13/22; qcur=0

Access control for Layer 7 requests

The http-request statement defines a set of rules which apply to layer 7
processing. The rules are evaluated in their declaration order when they are
met in a frontend, listen or backend section. Any rule may optionally be
followed by an ACL-based condition, in which case it will only be evaluated
if the condition is true.

The first keyword is the rule's action. The supported actions are described
below.

There is no limit to the number of http-request statements per instance.

It is important to know that http-request rules are processed very early in
the HTTP processing, just after "block" rules and before "reqdel" or "reqrep"
or "reqadd" rules. That way, headers added by "add-header"/"set-header" are
visible by almost all further ACL rules.

Using "reqadd"/"reqdel"/"reqrep" to manipulate request headers is discouraged
in newer versions (>= 1.5). But if you need to use regular expression to
delete headers, you can still use "reqdel". Also please use
"http-request deny/allow/tarpit" instead of "reqdeny"/"reqpass"/"reqtarpit".

acl nagios src 192.168.129.3
acl local_net src 192.168.0.0/16
acl auth_ok http_auth(L1)

http-request allow if nagios
http-request allow if local_net auth_ok
http-request auth realm Gimme if local_net auth_ok
http-request deny

acl key req.hdr(X-Add-Acl-Key) -m found
acl add path /addacl
acl del path /delacl

acl myhost hdr(Host) -f myhost.lst

http-request add-acl(myhost.lst) %[req.hdr(X-Add-Acl-Key)] if key add
http-request del-acl(myhost.lst) %[req.hdr(X-Add-Acl-Key)] if key del

acl value  req.hdr(X-Value) -m found
acl setmap path /setmap
acl delmap path /delmap

use_backend bk_appli if { hdr(Host),map_str(map.lst) -m found }

http-request set-map(map.lst) %[src] %[req.hdr(X-Value)] if setmap value
http-request del-map(map.lst) %[src]                     if delmap

This is used to add a new entry into an ACL. The ACL must be loaded from a
file (even a dummy empty file). The file name of the ACL to be updated is
passed between parentheses. It takes one argument: <key fmt>, which follows
log-format rules, to collect content of the new entry. It performs a lookup
in the ACL before insertion, to avoid duplicated (or more) values. This
lookup is done by a linear search and can be expensive with large lists!
It is the equivalent of the "add acl" command from the stats socket, but can
be triggered by an HTTP request.

This appends an HTTP header field whose name is specified in <name> and
whose value is defined by <fmt> which follows the log-format rules (see
Custom Log Format in section 8.2.4). This is particularly useful to pass
connection-specific information to the server (e.g. the client's SSL
certificate), or to combine several headers into one. This rule is not
final, so it is possible to add other similar rules. Note that header
addition is performed immediately, so one rule might reuse the resulting
header from a previous rule.

This stops the evaluation of the rules and lets the request pass the check.
No further "http-request" rules are evaluated.

This stops the evaluation of the rules and immediately responds with an
HTTP 401 or 407 error code to invite the user to present a valid user name
and password. No further "http-request" rules are evaluated. An optional
"realm" parameter is supported, it sets the authentication realm that is
returned with the response (typically the application's name).

acl auth_ok http_auth_group(L1) G1
http-request auth unless auth_ok

See section 10.2 about cache setup.

This captures sample expression <sample> from the request buffer, and
converts it to a string of at most <len> characters. The resulting string is
stored into the next request "capture" slot, so it will possibly appear next
to some captured HTTP headers. It will then automatically appear in the logs,
and it will be possible to extract it using sample fetch rules to feed it
into headers or anything. The length should be limited given that this size
will be allocated for each capture during the whole session life.
Please check section 7.3 (Fetching samples) and "capture request header" for
more information.

If the keyword "id" is used instead of "len", the action tries to store the
captured string in a previously declared capture slot. This is useful to run
captures in backends. The slot id can be declared by a previous directive
"http-request capture" or with the "declare capture" keyword.

When using this action in a backend, double check that the relevant
frontend(s) have the required capture slots otherwise, this rule will be
ignored at run time. This can't be detected at configuration parsing time
due to HAProxy's ability to dynamically resolve backend name at runtime.

This is used to delete an entry from an ACL. The ACL must be loaded from a
file (even a dummy empty file). The file name of the ACL to be updated is
passed between parentheses. It takes one argument: <key fmt>, which follows
log-format rules, to collect content of the entry to delete.
It is the equivalent of the "del acl" command from the stats socket, but can
be triggered by an HTTP request.

This removes all HTTP header fields whose name is specified in <name>.

This is used to delete an entry from a MAP. The MAP must be loaded from a
file (even a dummy empty file). The file name of the MAP to be updated is
passed between parentheses. It takes one argument: <key fmt>, which follows
log-format rules, to collect content of the entry to delete.
It takes one argument: "file name" It is the equivalent of the "del map"
command from the stats socket, but can be triggered by an HTTP request.

This stops the evaluation of the rules and immediately rejects the request
and emits an HTTP 403 error, or optionally the status code specified as an
argument to "deny_status". The list of permitted status codes is limited to
those that can be overridden by the "errorfile" directive.
No further "http-request" rules are evaluated.

This is used to build an HTTP 103 Early Hints response prior to any other one.
This appends an HTTP header field to this response whose name is specified in
<name> and whose value is defined by <fmt> which follows the log-format rules
(see Custom Log Format in section 8.2.4). This is particularly useful to pass
to the client some Link headers to preload resources required to render the
HTML documents.

See RFC 8297 for more information.

This performs an HTTP redirection based on a redirect rule. This is exactly
the same as the "redirect" statement except that it inserts a redirect rule
which can be processed in the middle of other "http-request" rules and that
these rules use the "log-format" strings. See the "redirect" keyword for the
rule's syntax.

This stops the evaluation of the rules and immediately closes the connection
without sending any response. It acts similarly to the
"tcp-request content reject" rules. It can be useful to force an immediate
connection closure on HTTP/2 connections.

This  matches the regular expression in all occurrences of header field
<name> according to <match-regex>, and replaces them with the
<replace-fmt> argument. Format characters are allowed in replace-fmt and
work like in <fmt> arguments in "http-request add-header". The match is
only case-sensitive. It is important to understand that this action only
considers whole header lines, regardless of the number of values they may
contain. This usage is suited to headers naturally containing commas in
their value, such as If-Modified-Since and so on.

http-request replace-header Cookie foo=([^;]*);(.*) foo=\1;ip=%bi;\2

# applied to:
Cookie: foo=foobar; expires=Tue, 14-Jun-2016 01:40:45 GMT;

# outputs:
Cookie: foo=foobar;ip=192.168.1.20; expires=Tue, 14-Jun-2016 01:40:45 GMT;

# assuming the backend IP is 192.168.1.20

This works like "replace-header" except that it matches the regex against
every comma-delimited value of the header field <name> instead of the
entire header. This is suited for all headers which are allowed to carry
more than one value. An example could be the Accept header.

http-request replace-value X-Forwarded-For ^192\.168\.(.*)$ 172.16.\1

# applied to:
X-Forwarded-For: 192.168.10.1, 192.168.13.24, 10.0.0.37

# outputs:
X-Forwarded-For: 172.16.10.1, 172.16.13.24, 10.0.0.37

This actions increments the GPC0 or GPC1 counter according with the sticky
counter designated by <sc-id>. If an error occurs, this action silently fails
and the actions evaluation continues.

This action sets the GPT0 tag according to the sticky counter designated by
<sc-id> and the value of <int>. The expected result is a boolean. If an error
occurs, this action silently fails and the actions evaluation continues.

This is used to set the destination IP address to the value of specified
expression. Useful when a proxy in front of HAProxy rewrites destination IP,
but provides the correct IP in a HTTP header; or you want to mask the IP for
privacy. If you want to connect to the new address/port, use '0.0.0.0:0' as a
server address in the backend.

<expr>  Is a standard HAProxy expression formed by a sample-fetch followed
        by some converters.

http-request set-dst hdr(x-dst)
http-request set-dst dst,ipmask(24)

When possible, set-dst preserves the original destination port as long as the
address family allows it, otherwise the destination port is set to 0.

This is used to set the destination port address to the value of specified
expression. If you want to connect to the new address/port, use '0.0.0.0:0'
as a server address in the backend.

<expr>  Is a standard HAProxy expression formed by a sample-fetch
        followed by some converters.

http-request set-dst-port hdr(x-port)
http-request set-dst-port int(4000)

When possible, set-dst-port preserves the original destination address as
long as the address family supports a port, otherwise it forces the
destination address to IPv4 "0.0.0.0" before rewriting the port.

This does the same as "http-request add-header" except that the header name
is first removed if it existed. This is useful when passing security
information to the server, where the header must not be manipulated by
external users. Note that the new value is computed before the removal so it
is possible to concatenate a value to an existing header.

http-request set-header X-Haproxy-Current-Date %T
http-request set-header X-SSL                  %[ssl_fc]
http-request set-header X-SSL-Session_ID       %[ssl_fc_session_id,hex]
http-request set-header X-SSL-Client-Verify    %[ssl_c_verify]
http-request set-header X-SSL-Client-DN        %{+Q}[ssl_c_s_dn]
http-request set-header X-SSL-Client-CN        %{+Q}[ssl_c_s_dn(cn)]
http-request set-header X-SSL-Issuer           %{+Q}[ssl_c_i_dn]
http-request set-header X-SSL-Client-NotBefore %{+Q}[ssl_c_notbefore]
http-request set-header X-SSL-Client-NotAfter  %{+Q}[ssl_c_notafter]

This is used to change the log level of the current request when a certain
condition is met. Valid levels are the 8 syslog levels (see the "log"
keyword) plus the special level "silent" which disables logging for this
request. This rule is not final so the last matching rule wins. This rule
can be useful to disable health checks coming from another equipment.

This is used to add a new entry into a MAP. The MAP must be loaded from a
file (even a dummy empty file). The file name of the MAP to be updated is
passed between parentheses. It takes 2 arguments: <key fmt>, which follows
log-format rules, used to collect MAP key, and <value fmt>, which follows
log-format rules, used to collect content for the new entry.
It performs a lookup in the MAP before insertion, to avoid duplicated (or
more) values. This lookup is done by a linear search and can be expensive
with large lists! It is the equivalent of the "set map" command from the
stats socket, but can be triggered by an HTTP request.

This is used to set the Netfilter MARK on all packets sent to the client to
the value passed in <mark> on platforms which support it. This value is an
unsigned 32 bit value which can be matched by netfilter and by the routing
table. It can be expressed both in decimal or hexadecimal format (prefixed by
"0x"). This can be useful to force certain packets to take a different route
(for example a cheaper network path for bulk downloads). This works on Linux
kernels 2.6.32 and above and requires admin privileges.

This rewrites the request method with the result of the evaluation of format
string <fmt>. There should be very few valid reasons for having to do so as
this is more likely to break something than to fix it.

This sets the "nice" factor of the current request being processed. It only
has effect against the other requests being processed at the same time.
The default value is 0, unless altered by the "nice" setting on the "bind"
line. The accepted range is -1024..1024. The higher the value, the nicest
the request will be. Lower values will make the request more important than
other ones. This can be useful to improve the speed of some requests, or
lower the priority of non-important requests. Using this setting without
prior experimentation can cause some major slowdown.

This rewrites the request path with the result of the evaluation of format
string <fmt>. The query string, if any, is left intact. If a scheme and
authority is found before the path, they are left intact as well. If the
request doesn't have a path ("*"), this one is replaced with the format.
This can be used to prepend a directory component in front of a path for
example. See also "http-request set-query" and "http-request set-uri".

# prepend the host name before the path
http-request set-path /%[hdr(host)]%[path]

This is used to set the queue priority class of the current request.
The value must be a sample expression which converts to an integer in the
range -2047..2047. Results outside this range will be truncated.
The priority class determines the order in which queued requests are
processed. Lower values have higher priority.

This is used to set the queue priority timestamp offset of the current
request. The value must be a sample expression which converts to an integer
in the range -524287..524287. Results outside this range will be truncated.
When a request is queued, it is ordered first by the priority class, then by
the current timestamp adjusted by the given offset in milliseconds. Lower
values have higher priority.
Note that the resulting timestamp is is only tracked with enough precision
for 524,287ms (8m44s287ms). If the request is queued long enough to where the
adjusted timestamp exceeds this value, it will be misidentified as highest
priority. Thus it is important to set "timeout queue" to a value, where when
combined with the offset, does not exceed this limit.

This rewrites the request's query string which appears after the first
question mark ("?") with the result of the evaluation of format string <fmt>.
The part prior to the question mark is left intact. If the request doesn't
contain a question mark and the new value is not empty, then one is added at
the end of the URI, followed by the new value. If a question mark was
present, it will never be removed even if the value is empty. This can be
used to add or remove parameters from the query string.

See also "http-request set-query" and "http-request set-uri".

# replace "%3D" with "=" in the query string
http-request set-query %[query,regsub(%3D,=,g)]

This is used to set the source IP address to the value of specified
expression. Useful when a proxy in front of HAProxy rewrites source IP, but
provides the correct IP in a HTTP header; or you want to mask source IP for
privacy. All subsequent calls to "src" fetch will return this value
(see example).

<expr>  Is a standard HAProxy expression formed by a sample-fetch followed
        by some converters.

See also "option forwardfor".

http-request set-src hdr(x-forwarded-for)
http-request set-src src,ipmask(24)

# After the masking this will track connections
# based on the IP address with the last byte zeroed out.
http-request track-sc0 src

When possible, set-src preserves the original source port as long as the
address family allows it, otherwise the source port is set to 0.

This is used to set the source port address to the value of specified
expression.

<expr>  Is a standard HAProxy expression formed by a sample-fetch followed
        by some converters.

http-request set-src-port hdr(x-port)
http-request set-src-port int(4000)

When possible, set-src-port preserves the original source address as long as
the address family supports a port, otherwise it forces the source address to
IPv4 "0.0.0.0" before rewriting the port.

This is used to set the TOS or DSCP field value of packets sent to the client
to the value passed in <tos> on platforms which support this. This value
represents the whole 8 bits of the IP TOS field, and can be expressed both in
decimal or hexadecimal format (prefixed by "0x"). Note that only the 6 higher
bits are used in DSCP or TOS, and the two lower bits are always 0. This can
be used to adjust some routing behavior on border routers based on some
information from the request.

See RFC 2474, 2597, 3260 and 4594 for more information.

This rewrites the request URI with the result of the evaluation of format
string <fmt>. The scheme, authority, path and query string are all replaced
at once. This can be used to rewrite hosts in front of proxies, or to
perform complex modifications to the URI such as moving parts between the
path and the query string.
See also "http-request set-path" and "http-request set-query".

This is used to set the contents of a variable. The variable is declared
inline.

<var-name>  The name of the variable starts with an indication about its
            scope. The scopes allowed are:
              "proc" : the variable is shared with the whole process
              "sess" : the variable is shared with the whole session
              "txn"  : the variable is shared with the transaction
                       (request and response)
              "req"  : the variable is shared only during request
                       processing
              "res"  : the variable is shared only during response
                       processing
            This prefix is followed by a name. The separator is a '.'.
            The name may only contain characters 'a-z', 'A-Z', '0-9'
            and '_'.

<expr>      Is a standard HAProxy expression formed by a sample-fetch
            followed by some converters.

http-request set-var(req.my_var) req.fhdr(user-agent),lower

This action is used to trigger sending of a group of SPOE messages. To do so,
the SPOE engine used to send messages must be defined, as well as the SPOE
group to send. Of course, the SPOE engine must refer to an existing SPOE
filter. If not engine name is provided on the SPOE filter line, the SPOE
agent name must be used.

<engine-name>  The SPOE engine name.

<group-name>   The SPOE group name as specified in the engine
               configuration.

This stops the evaluation of the rules and makes the client-facing connection
suddenly disappear using a system-dependent way that tries to prevent the
client from being notified. The effect it then that the client still sees an
established connection while there's none on HAProxy. The purpose is to
achieve a comparable effect to "tarpit" except that it doesn't use any local
resource at all on the machine running HAProxy. It can resist much higher
loads than "tarpit", and slow down stronger attackers. It is important to
understand the impact of using this mechanism. All stateful equipment placed
between the client and HAProxy (firewalls, proxies, load balancers) will also
keep the established connection for a long time and may suffer from this
action.
On modern Linux systems running with enough privileges, the TCP_REPAIR socket
option is used to block the emission of a TCP reset. On other systems, the
socket's TTL is reduced to 1 so that the TCP reset doesn't pass the first
router, though it's still delivered to local networks. Do not use it unless
you fully understand how it works.

This stops the evaluation of the rules and immediately blocks the request
without responding for a delay specified by "timeout tarpit" or
"timeout connect" if the former is not set. After that delay, if the client
is still connected, an HTTP error 500 (or optionally the status code
specified as an argument to "deny_status") is returned so that the client
does not suspect it has been tarpitted. Logs will report the flags "PT".
The goal of the tarpit rule is to slow down robots during an attack when
they're limited on the number of concurrent requests. It can be very
efficient against very dumb robots, and will significantly reduce the load
on firewalls compared to a "deny" rule. But when facing "correctly"
developed robots, it can make things worse by forcing haproxy and the front
firewall to support insane number of concurrent connections.
See also the "silent-drop" action.

This enables tracking of sticky counters from current request. These rules do
not stop evaluation and do not change default action. The number of counters
that may be simultaneously tracked by the same connection is set in
MAX_SESS_STKCTR at build time (reported in haproxy -vv) which defaults to 3,
so the track-sc number is between 0 and (MAX_SESS_STCKTR-1). The first
"track-sc0" rule executed enables tracking of the counters of the specified
table as the first set. The first "track-sc1" rule executed enables tracking
of the counters of the specified table as the second set. The first
"track-sc2" rule executed enables tracking of the counters of the specified
table as the third set. It is a recommended practice to use the first set of
counters for the per-frontend counters and the second set for the per-backend
ones. But this is just a guideline, all may be used everywhere.

<key>   is mandatory, and is a sample expression rule as described in
        section 7.3. It describes what elements of the incoming request or
        connection will be analyzed, extracted, combined, and used to
        select which table entry to update the counters.

<table> is an optional table to be used instead of the default one, which
        is the stick-table declared in the current proxy. All the counters
        for the matches and updates for the key will then be performed in
        that table until the session ends.

Once a "track-sc*" rule is executed, the key is looked up in the table and if
it is not found, an entry is allocated for it. Then a pointer to that entry
is kept during all the session's life, and this entry's counters are updated
as often as possible, every time the session's counters are updated, and also
systematically when the session ends. Counters are only updated for events
that happen after the tracking has been started. As an exception, connection
counters and request counters are systematically updated so that they reflect
useful information.

If the entry tracks concurrent connection counters, one connection is counted
for as long as the entry is tracked, and the entry will not expire during
that time. Tracking counters also provides a performance advantage over just
checking the keys, because only one table lookup is performed for all ACL
checks that make use of it.

This is used to unset a variable. See above for details about <var-name>.

http-request unset-var(req.my_var)

This directive executes the configured HTTP service to reply to the request
and stops the evaluation of the rules. An HTTP service may choose to reply by
sending any valid HTTP response or it may immediately close the connection
without sending any response. Outside natives services, for instance the
Prometheus exporter, it is possible to write your own services in Lua. No
further "http-request" rules are evaluated.

<service-name>  is mandatory. It is the service to call

http-request use-service prometheus-exporter if { path /metrics }

This will delay the processing of the request until the SSL handshake
happened. This is mostly useful to delay processing early data until we're
sure they are valid.

Access control for Layer 7 responses

The http-response statement defines a set of rules which apply to layer 7
processing. The rules are evaluated in their declaration order when they are
met in a frontend, listen or backend section. Any rule may optionally be
followed by an ACL-based condition, in which case it will only be evaluated
if the condition is true. Since these rules apply on responses, the backend
rules are applied first, followed by the frontend's rules.

The first keyword is the rule's action. The supported actions are described
below.

There is no limit to the number of http-response statements per instance.

It is important to know that http-response rules are processed very early in
the HTTP processing, before "rspdel" or "rsprep" or "rspadd" rules. That way,
headers added by "add-header"/"set-header" are visible by almost all further
ACL rules.

Using "rspadd"/"rspdel"/"rsprep" to manipulate request headers is discouraged
in newer versions (>= 1.5). But if you need to use regular expression to
delete headers, you can still use "rspdel". Also please use
"http-response deny" instead of "rspdeny".

acl key_acl res.hdr(X-Acl-Key) -m found

acl myhost hdr(Host) -f myhost.lst

http-response add-acl(myhost.lst) %[res.hdr(X-Acl-Key)] if key_acl
http-response del-acl(myhost.lst) %[res.hdr(X-Acl-Key)] if key_acl

acl value  res.hdr(X-Value) -m found

use_backend bk_appli if { hdr(Host),map_str(map.lst) -m found }

http-response set-map(map.lst) %[src] %[res.hdr(X-Value)] if value
http-response del-map(map.lst) %[src]                     if ! value

This is used to add a new entry into an ACL. The ACL must be loaded from a
file (even a dummy empty file). The file name of the ACL to be updated is
passed between parentheses. It takes one argument: <key fmt>, which follows
log-format rules, to collect content of the new entry. It performs a lookup
in the ACL before insertion, to avoid duplicated (or more) values.
This lookup is done by a linear search and can be expensive with large lists!
It is the equivalent of the "add acl" command from the stats socket, but can
be triggered by an HTTP response.

This appends an HTTP header field whose name is specified in <name> and whose
value is defined by <fmt> which follows the log-format rules (see Custom Log
Format in section 8.2.4). This may be used to send a cookie to a client for
example, or to pass some internal information.
This rule is not final, so it is possible to add other similar rules.
Note that header addition is performed immediately, so one rule might reuse
the resulting header from a previous rule.

This stops the evaluation of the rules and lets the response pass the check.
No further "http-response" rules are evaluated for the current section.

See section 10.2 about cache setup.

This captures sample expression <sample> from the response buffer, and
converts it to a string. The resulting string is stored into the next request
"capture" slot, so it will possibly appear next to some captured HTTP
headers. It will then automatically appear in the logs, and it will be
possible to extract it using sample fetch rules to feed it into headers or
anything. Please check section 7.3 (Fetching samples) and
"capture response header" for more information.

The keyword "id" is the id of the capture slot which is used for storing the
string. The capture slot must be defined in an associated frontend.
This is useful to run captures in backends. The slot id can be declared by a
previous directive "http-response capture" or with the "declare capture"
keyword.

When using this action in a backend, double check that the relevant
frontend(s) have the required capture slots otherwise, this rule will be
ignored at run time. This can't be detected at configuration parsing time
due to HAProxy's ability to dynamically resolve backend name at runtime.

This is used to delete an entry from an ACL. The ACL must be loaded from a
file (even a dummy empty file). The file name of the ACL to be updated is
passed between parentheses. It takes one argument: <key fmt>, which follows
log-format rules, to collect content of the entry to delete.
It is the equivalent of the "del acl" command from the stats socket, but can
be triggered by an HTTP response.

This removes all HTTP header fields whose name is specified in <name>.

This is used to delete an entry from a MAP. The MAP must be loaded from a
file (even a dummy empty file). The file name of the MAP to be updated is
passed between parentheses. It takes one argument: <key fmt>, which follows
log-format rules, to collect content of the entry to delete.
It takes one argument: "file name" It is the equivalent of the "del map"
command from the stats socket, but can be triggered by an HTTP response.

This stops the evaluation of the rules and immediately rejects the response
and emits an HTTP 502 error. No further "http-response" rules are evaluated.

This performs an HTTP redirection based on a redirect rule.
This supports a format string similarly to "http-request redirect" rules,
with the exception that only the "location" type of redirect is possible on
the response. See the "redirect" keyword for the rule's syntax. When a
redirect rule is applied during a response, connections to the server are
closed so that no data can be forwarded from the server to the client.

This matches the regular expression in all occurrences of header field <name>
according to <match-regex>, and replaces them with the <replace-fmt> argument.
Format characters are allowed in replace-fmt and work like in <fmt> arguments
in "add-header". The match is only case-sensitive. It is important to
understand that this action only considers whole header lines, regardless of
the number of values they may contain. This usage is suited to headers
naturally containing commas in their value, such as Set-Cookie, Expires and
so on.

http-response replace-header Set-Cookie (C=[^;]*);(.*) \1;ip=%bi;\2

# applied to:
Set-Cookie: C=1; expires=Tue, 14-Jun-2016 01:40:45 GMT

# outputs:
Set-Cookie: C=1;ip=192.168.1.20; expires=Tue, 14-Jun-2016 01:40:45 GMT

# assuming the backend IP is 192.168.1.20.

This works like "replace-header" except that it matches the regex against
every comma-delimited value of the header field <name> instead of the entire
header. This is suited for all headers which are allowed to carry more than
one value. An example could be the Accept header.

http-response replace-value Cache-control ^public$ private

# applied to:
Cache-Control: max-age=3600, public

# outputs:
Cache-Control: max-age=3600, private

This action increments the GPC0 or GPC1 counter according with the sticky
counter designated by <sc-id>. If an error occurs, this action silently fails
and the actions evaluation continues.

This action sets the GPT0 tag according to the sticky counter designated by
<sc-id> and the value of <int>. The expected result is a boolean. If an error
occurs, this action silently fails and the actions evaluation continues.

This action is used to trigger sending of a group of SPOE messages. To do so,
the SPOE engine used to send messages must be defined, as well as the SPOE
group to send. Of course, the SPOE engine must refer to an existing SPOE
filter. If not engine name is provided on the SPOE filter line, the SPOE
agent name must be used.

<engine-name>  The SPOE engine name.

<group-name>   The SPOE group name as specified in the engine
               configuration.

This does the same as "add-header" except that the header name is first
removed if it existed. This is useful when passing security information to
the server, where the header must not be manipulated by external users.

This is used to change the log level of the current request when a certain
condition is met. Valid levels are the 8 syslog levels (see the "log"
keyword) plus the special level "silent" which disables logging for this
request. This rule is not final so the last matching rule wins. This rule can
be useful to disable health checks coming from another equipment.

This is used to add a new entry into a MAP. The MAP must be loaded from a
file (even a dummy empty file). The file name of the MAP to be updated is
passed between parentheses. It takes 2 arguments: <key fmt>, which follows
log-format rules, used to collect MAP key, and <value fmt>, which follows
log-format rules, used to collect content for the new entry. It performs a
lookup in the MAP before insertion, to avoid duplicated (or more) values.
This lookup is done by a linear search and can be expensive with large lists!
It is the equivalent of the "set map" command from the stats socket, but can
be triggered by an HTTP response.

This is used to set the Netfilter MARK on all packets sent to the client to
the value passed in <mark> on platforms which support it. This value is an
unsigned 32 bit value which can be matched by netfilter and by the routing
table. It can be expressed both in decimal or hexadecimal format (prefixed
by "0x"). This can be useful to force certain packets to take a different
route (for example a cheaper network path for bulk downloads). This works on
Linux kernels 2.6.32 and above and requires admin privileges.

This sets the "nice" factor of the current request being processed.
It only has effect against the other requests being processed at the same
time. The default value is 0, unless altered by the "nice" setting on the
"bind" line. The accepted range is -1024..1024. The higher the value, the
nicest the request will be. Lower values will make the request more important
than other ones. This can be useful to improve the speed of some requests, or
lower the priority of non-important requests. Using this setting without
prior experimentation can cause some major slowdown.

This replaces the response status code with <status> which must be an integer
between 100 and 999. Optionally, a custom reason text can be provided defined
by <str>, or the default reason for the specified code will be used as a
fallback.

# return "431 Request Header Fields Too Large"
http-response set-status 431
# return "503 Slow Down", custom reason
http-response set-status 503 reason "Slow Down".

This is used to set the TOS or DSCP field value of packets sent to the client
to the value passed in <tos> on platforms which support this.
This value represents the whole 8 bits of the IP TOS field, and can be
expressed both in decimal or hexadecimal format (prefixed by "0x"). Note that
only the 6 higher bits are used in DSCP or TOS, and the two lower bits are
always 0. This can be used to adjust some routing behavior on border routers
based on some information from the request.

See RFC 2474, 2597, 3260 and 4594 for more information.

This is used to set the contents of a variable. The variable is declared
inline.

<var-name>  The name of the variable starts with an indication about its
            scope. The scopes allowed are:
              "proc" : the variable is shared with the whole process
              "sess" : the variable is shared with the whole session
              "txn"  : the variable is shared with the transaction
                       (request and response)
              "req"  : the variable is shared only during request
                       processing
              "res"  : the variable is shared only during response
                       processing
            This prefix is followed by a name. The separator is a '.'.
            The name may only contain characters 'a-z', 'A-Z', '0-9', '.'
            and '_'.

<expr>      Is a standard HAProxy expression formed by a sample-fetch
            followed by some converters.

http-response set-var(sess.last_redir) res.hdr(location)

This stops the evaluation of the rules and makes the client-facing connection
suddenly disappear using a system-dependent way that tries to prevent the
client from being notified. The effect it then that the client still sees an
established connection while there's none on HAProxy. The purpose is to
achieve a comparable effect to "tarpit" except that it doesn't use any local
resource at all on the machine running HAProxy. It can resist much higher
loads than "tarpit", and slow down stronger attackers. It is important to
understand the impact of using this mechanism. All stateful equipment placed
between the client and HAProxy (firewalls, proxies, load balancers) will also
keep the established connection for a long time and may suffer from this
action.
On modern Linux systems running with enough privileges, the TCP_REPAIR socket
option is used to block the emission of a TCP reset. On other systems, the
socket's TTL is reduced to 1 so that the TCP reset doesn't pass the first
router, though it's still delivered to local networks. Do not use it unless
you fully understand how it works.

This enables tracking of sticky counters from current response. Please refer
to "http-request track-sc" for a complete description. The only difference
from "http-request track-sc" is the <key> sample expression can only make use
of samples in response (e.g. res.*, status etc.) and samples below Layer 6
(e.g. SSL-related samples, see section 7.3.4). If the sample is not
supported, haproxy will fail and warn while parsing the config.

This is used to unset a variable. See "http-response set-var" for details
about <var-name>.

http-response unset-var(sess.last_redir)

Declare how idle HTTP connections may be shared between requests

By default, a connection established between haproxy and the backend server
which is considered safe for reuse is moved back to the server's idle
connections pool so that any other request can make use of it. This is the
"safe" strategy below.

The argument indicates the desired connection reuse strategy :

  - "never"  : idle connections are never shared between sessions. This mode
               may be enforced to cancel a different strategy inherited from
               a defaults section or for troubleshooting. For example, if an
               old bogus application considers that multiple requests over
               the same connection come from the same client and it is not
               possible to fix the application, it may be desirable to
               disable connection sharing in a single backend. An example of
               such an application could be an old haproxy using cookie
               insertion in tunnel mode and not checking any request past the
               first one.

  - "safe"   : this is the default and the recommended strategy. The first
               request of a session is always sent over its own connection,
               and only subsequent requests may be dispatched over other
               existing connections. This ensures that in case the server
               closes the connection when the request is being sent, the
               browser can decide to silently retry it. Since it is exactly
               equivalent to regular keep-alive, there should be no side
               effects.

  - "aggressive" : this mode may be useful in webservices environments where
               all servers are not necessarily known and where it would be
               appreciable to deliver most first requests over existing
               connections. In this case, first requests are only delivered
               over existing connections that have been reused at least once,
               proving that the server correctly supports connection reuse.
               It should only be used when it's sure that the client can
               retry a failed request once in a while and where the benefit
               of aggressive connection reuse significantly outweighs the
               downsides of rare connection failures.

  - "always" : this mode is only recommended when the path to the server is
               known for never breaking existing connections quickly after
               releasing them. It allows the first request of a session to be
               sent to an existing connection. This can provide a significant
               performance increase over the "safe" strategy when the backend
               is a cache farm, since such components tend to show a
               consistent behavior and will benefit from the connection
               sharing. It is recommended that the "http-keep-alive" timeout
               remains low in this mode so that no dead connections remain
               usable. In most cases, this will lead to the same performance
               gains as "aggressive" but with more risks. It should only be
               used when it improves the situation over "aggressive".

When http connection sharing is enabled, a great care is taken to respect the
connection properties and compatibility. Specifically :
  - connections made with "usesrc" followed by a client-dependent value
    ("client", "clientip", "hdr_ip") are marked private and never shared;

  - connections sent to a server with a TLS SNI extension are marked private
    and are never shared;

  - connections with certain bogus authentication schemes (relying on the
    connection) like NTLM are detected, marked private and are never shared;

A connection pool is involved and configurable with "pool-max-conn".

Note: connection reuse improves the accuracy of the "server maxconn" setting,
because almost no new connection will be established while idle connections
remain available. This is particularly true with the "always" strategy.

Add the server name to a request. Use the header string given by <header>

<header>  The header string to use to send the server name

The "http-send-name-header" statement causes the header field named <header>
to be set to the name of the target server at the moment the request is about
to be sent on the wire. Any existing occurrences of this header are removed.
Upon retries and redispatches, the header field is updated to always reflect
the server being attempted to connect to. Given that this header is modified
very late in the connection setup, it may have unexpected effects on already
modified headers. For example using it with transport-level header such as
connection, content-length, transfer-encoding and so on will likely result in
invalid requests being sent to the server. Additionally it has been reported
that this directive is currently being used as a way to overwrite the Host
header field in outgoing requests; while this trick has been known to work
as a side effect of the feature for some time, it is not officially supported
and might possibly not work anymore in a future version depending on the
technical difficulties this feature induces. A long-term solution instead
consists in fixing the application which required this trick so that it binds
to the correct host name.

Set a persistent ID to a proxy.

Set a persistent ID for the proxy. This ID must be unique and positive.
An unused ID will automatically be assigned if unset. The first assigned
value will be 1. This ID is currently only returned in statistics.

Declare a condition to ignore persistence

By default, when cookie persistence is enabled, every requests containing
the cookie are unconditionally persistent (assuming the target server is up
and running).

The "ignore-persist" statement allows one to declare various ACL-based
conditions which, when met, will cause a request to ignore persistence.
This is sometimes useful to load balance requests for static files, which
often don't require persistence. This can also be used to fully disable
persistence for a specific User-Agent (for example, some web crawler bots).

The persistence is ignored when an "if" condition is met, or unless an
"unless" condition is met.

acl url_static  path_beg         /static /images /img /css
acl url_static  path_end         .gif .png .jpg .css .js
ignore-persist  if url_static

Allow seamless reload of HAProxy

This directive points HAProxy to a file where server state from previous
running process has been saved. That way, when starting up, before handling
traffic, the new process can apply old states to servers exactly has if no
reload occurred. The purpose of the "load-server-state-from-file" directive is
to tell haproxy which file to use. For now, only 2 arguments to either prevent
loading state or load states from a file containing all backends and servers.
The state file can be generated by running the command "show servers state"
over the stats socket and redirect output.

The format of the file is versioned and is very specific. To understand it,
please read the documentation of the "show servers state" command (chapter
9.3 of Management Guide).

global     load the content of the file pointed by the global directive
           named "server-state-file".

local      load the content of the file pointed by the directive
           "server-state-file-name" if set. If not set, then the backend
           name is used as a file name.

none       don't load any stat for this backend

Notes:
  - server's IP address is preserved across reloads by default, but the
    order can be changed thanks to the server's "init-addr" setting. This
    means that an IP address change performed on the CLI at run time will
    be preserved, and that any change to the local resolver (e.g. /etc/hosts)
    will possibly not have any effect if the state file is in use.

  - server's weight is applied from previous running process unless it has
    has changed between previous and new configuration files.

Minimal configuration
global
 stats socket /tmp/socket
 server-state-file /tmp/server_state

defaults
 load-server-state-from-file global

backend bk
 server s1 127.0.0.1:22 check weight 11
 server s2 127.0.0.1:22 check weight 12

Then one can run :

  socat /tmp/socket - <<< "show servers state" > /tmp/server_state

Content of the file /tmp/server_state would be like this:

  1
  # <field names skipped for the doc example>
  1 bk 1 s1 127.0.0.1 2 0 11 11 4 6 3 4 6 0 0
  1 bk 2 s2 127.0.0.1 2 0 12 12 4 6 3 4 6 0 0

Minimal configuration
global
 stats socket /tmp/socket
 server-state-base /etc/haproxy/states

defaults
 load-server-state-from-file local

backend bk
 server s1 127.0.0.1:22 check weight 11
 server s2 127.0.0.1:22 check weight 12

Then one can run :

  socat /tmp/socket - <<< "show servers state bk" > /etc/haproxy/states/bk

Content of the file /etc/haproxy/states/bk would be like this:

  1
  # <field names skipped for the doc example>
  1 bk 1 s1 127.0.0.1 2 0 11 11 4 6 3 4 6 0 0
  1 bk 2 s2 127.0.0.1 2 0 12 12 4 6 3 4 6 0 0

Enable per-instance logging of events and traffic.

Prefix :
  no         should be used when the logger list must be flushed. For example,
             if you don't want to inherit from the default logger list. This
             prefix does not allow arguments.

global     should be used when the instance's logging parameters are the
           same as the global ones. This is the most common usage. "global"
           replaces <address>, <facility> and <level> with those of the log
           entries found in the "global" section. Only one "log global"
           statement may be used per instance, and this form takes no other
           parameter.

<address>  indicates where to send the logs. It takes the same format as
           for the "global" section's logs, and can be one of :

           - An IPv4 address optionally followed by a colon (':') and a UDP
             port. If no port is specified, 514 is used by default (the
             standard syslog port).

           - An IPv6 address followed by a colon (':') and optionally a UDP
             port. If no port is specified, 514 is used by default (the
             standard syslog port).

           - A filesystem path to a UNIX domain socket, keeping in mind
             considerations for chroot (be sure the path is accessible
             inside the chroot) and uid/gid (be sure the path is
             appropriately writable).

           - A file descriptor number in the form "fd@<number>", which may
             point to a pipe, terminal, or socket. In this case unbuffered
             logs are used and one writev() call per log is performed. This
             is a bit expensive but acceptable for most workloads. Messages
             sent this way will not be truncated but may be dropped, in
             which case the DroppedLogs counter will be incremented. The
             writev() call is atomic even on pipes for messages up to
             PIPE_BUF size, which POSIX recommends to be at least 512 and
             which is 4096 bytes on most modern operating systems. Any
             larger message may be interleaved with messages from other
             processes.  Exceptionally for debugging purposes the file
             descriptor may also be directed to a file, but doing so will
             significantly slow haproxy down as non-blocking calls will be
             ignored. Also there will be no way to purge nor rotate this
             file without restarting the process. Note that the configured
             syslog format is preserved, so the output is suitable for use
             with a TCP syslog server. See also the "short" and "raw"
             formats below.

           - "stdout" / "stderr", which are respectively aliases for "fd@1"
             and "fd@2", see above.

           You may want to reference some environment variables in the
           address parameter, see section 2.3 about environment variables.

<length>   is an optional maximum line length. Log lines larger than this
           value will be truncated before being sent. The reason is that
           syslog servers act differently on log line length. All servers
           support the default value of 1024, but some servers simply drop
           larger lines while others do log them. If a server supports long
           lines, it may make sense to set this value here in order to avoid
           truncating long lines. Similarly, if a server drops long lines,
           it is preferable to truncate them before sending them. Accepted
           values are 80 to 65535 inclusive. The default value of 1024 is
           generally fine for all standard usages. Some specific cases of
           long captures or JSON-formatted logs may require larger values.

<format> is the log format used when generating syslog messages. It may be
         one of the following :

  rfc3164   The RFC3164 syslog message format. This is the default.
            (https://tools.ietf.org/html/rfc3164)

  rfc5424   The RFC5424 syslog message format.
            (https://tools.ietf.org/html/rfc5424)

  short     A message containing only a level between angle brackets such as
            '<3>', followed by the text. The PID, date, time, process name
            and system name are omitted. This is designed to be used with a
            local log server. This format is compatible with what the
            systemd logger consumes.

  raw       A message containing only the text. The level, PID, date, time,
            process name and system name are omitted. This is designed to
            be used in containers or during development, where the severity
            only depends on the file descriptor used (stdout/stderr).

<facility> must be one of the 24 standard syslog facilities :

               kern   user   mail   daemon auth   syslog lpr    news
               uucp   cron   auth2  ftp    ntp    audit  alert  cron2
               local0 local1 local2 local3 local4 local5 local6 local7

           Note that the facility is ignored for the "short" and "raw"
           formats, but still required as a positional field. It is
           recommended to use "daemon" in this case to make it clear that
           it's only supposed to be used locally.

<level>    is optional and can be specified to filter outgoing messages. By
           default, all messages are sent. If a level is specified, only
           messages with a severity at least as important as this level
           will be sent. An optional minimum level can be specified. If it
           is set, logs emitted with a more severe level than this one will
           be capped to this level. This is used to avoid sending "emerg"
           messages on all terminals on some default syslog configurations.
           Eight levels are known :

             emerg  alert  crit   err    warning notice info  debug

It is important to keep in mind that it is the frontend which decides what to
log from a connection, and that in case of content switching, the log entries
from the backend will be ignored. Connections are logged at level "info".

However, backend log declaration define how and where servers status changes
will be logged. Level "notice" will be used to indicate a server going up,
"warning" will be used for termination signals and definitive service
termination, and "alert" will be used for when a server goes down.

Note : According to RFC3164, messages are truncated to 1024 bytes before
       being emitted.

log global
log stdout format short daemon          # send log to systemd
log stdout format raw daemon            # send everything to stdout
log stderr format raw daemon notice     # send important events to stderr
log 127.0.0.1:514 local0 notice         # only send important events
log 127.0.0.1:514 local0 notice notice  # same but limit output level
log "${LOCAL_SYSLOG}:514" local0 notice   # send to local server

Specifies the log format string to use for traffic logs

This directive specifies the log format string that will be used for all logs
resulting from traffic passing through the frontend using this line. If the
directive is used in a defaults section, all subsequent frontends will use
the same log format. Please see section 8.2.4 which covers the log format
string in depth.

"log-format" directive overrides previous "option tcplog", "log-format" and
"option httplog" directives.

Specifies the RFC5424 structured-data log format string

This directive specifies the RFC5424 structured-data log format string that
will be used for all logs resulting from traffic passing through the frontend
using this line. If the directive is used in a defaults section, all
subsequent frontends will use the same log format. Please see section 8.2.4
which covers the log format string in depth.

See https://tools.ietf.org/html/rfc5424#section-6.3 for more information
about the RFC5424 structured-data part.

Note : This log format string will be used only for loggers that have set
       log format to "rfc5424".

log-format-sd [exampleSDID@1234\ bytes=\"%B\"\ status=\"%ST\"]

Specifies the log tag to use for all outgoing logs

Sets the tag field in the syslog header to this string. It defaults to the
log-tag set in the global section, otherwise the program name as launched
from the command line, which usually is "haproxy". Sometimes it can be useful
to differentiate between multiple processes running on the same host, or to
differentiate customer instances running in the same process. In the backend,
logs about servers up/down will use this tag. As a hint, it can be convenient
to set a log-tag related to a hosted customer in a defaults section then put
all the frontends and backends for that customer, then start another customer
in a new defaults section. See also the global "log-tag" directive.

Set the maximum server queue size for maintaining keep-alive connections

HTTP keep-alive tries to reuse the same server connection whenever possible,
but sometimes it can be counter-productive, for example if a server has a lot
of connections while other ones are idle. This is especially true for static
servers.

The purpose of this setting is to set a threshold on the number of queued
connections at which haproxy stops trying to reuse the same server and prefers
to find another one. The default value, -1, means there is no limit. A value
of zero means that keep-alive requests will never be queued. For very close
servers which can be reached with a low latency and which are not sensible to
breaking keep-alive, a low value is recommended (e.g. local static server can
use a value of 10 or less). For remote servers suffering from a high latency,
higher values might be needed to cover for the latency and/or the cost of
picking a different server.

Note that this has no impact on responses which are maintained to the same
server consecutively to a 401 response. They will still go to the same server
even if they have to be queued.

Set the maximum number of outgoing connections we can keep idling for a given
client session. The default is 5 (it precisely equals MAX_SRV_LIST which is
defined at build time).

Fix the maximum number of concurrent connections on a frontend

<conns>   is the maximum number of concurrent connections the frontend will
          accept to serve. Excess connections will be queued by the system
          in the socket's listen queue and will be served once a connection
          closes.

If the system supports it, it can be useful on big sites to raise this limit
very high so that haproxy manages connection queues, instead of leaving the
clients with unanswered connection attempts. This value should not exceed the
global maxconn. Also, keep in mind that a connection contains two buffers
of tune.bufsize (16kB by default) each, as well as some other data resulting
in about 33 kB of RAM being consumed per established connection. That means
that a medium system equipped with 1GB of RAM can withstand around
20000-25000 concurrent connections if properly tuned.

Also, when <conns> is set to large values, it is possible that the servers
are not sized to accept such loads, and for this reason it is generally wise
to assign them some reasonable connection limits.

By default, this value is set to 2000.

Set the running mode or protocol of the instance

tcp       The instance will work in pure TCP mode. A full-duplex connection
          will be established between clients and servers, and no layer 7
          examination will be performed. This is the default mode. It
          should be used for SSL, SSH, SMTP, ...

http      The instance will work in HTTP mode. The client request will be
          analyzed in depth before connecting to any server. Any request
          which is not RFC-compliant will be rejected. Layer 7 filtering,
          processing and switching will be possible. This is the mode which
          brings HAProxy most of its value.

health    The instance will work in "health" mode. It will just reply "OK"
          to incoming connections and close the connection. Alternatively,
          If the "httpchk" option is set, "HTTP/1.0 200 OK" will be sent
          instead. Nothing will be logged in either case. This mode is used
          to reply to external components health checks. This mode is
          deprecated and should not be used anymore as it is possible to do
          the same and even better by combining TCP or HTTP modes with the
          "monitor" keyword.

When doing content switching, it is mandatory that the frontend and the
backend are in the same mode (generally HTTP), otherwise the configuration
will be refused.

defaults http_instances
    mode http

Add a condition to report a failure to a monitor HTTP request.

if <cond>     the monitor request will fail if the condition is satisfied,
              and will succeed otherwise. The condition should describe a
              combined test which must induce a failure if all conditions
              are met, for instance a low number of servers both in a
              backend and its backup.

unless <cond> the monitor request will succeed only if the condition is
              satisfied, and will fail otherwise. Such a condition may be
              based on a test on the presence of a minimum number of active
              servers in a list of backends.

This statement adds a condition which can force the response to a monitor
request to report a failure. By default, when an external component queries
the URI dedicated to monitoring, a 200 response is returned. When one of the
conditions above is met, haproxy will return 503 instead of 200. This is
very useful to report a site failure to an external component which may base
routing advertisements between multiple sites on the availability reported by
haproxy. In this case, one would rely on an ACL involving the "nbsrv"
criterion. Note that "monitor fail" only works in HTTP mode. Both status
messages may be tweaked using "errorfile" or "errorloc" if needed.

frontend www
   mode http
   acl site_dead nbsrv(dynamic) lt 2
   acl site_dead nbsrv(static)  lt 2
   monitor-uri   /site_alive
   monitor fail  if site_dead

Declare a source network which is limited to monitor requests

<source>  is the source IPv4 address or network which will only be able to
          get monitor responses to any request. It can be either an IPv4
          address, a host name, or an address followed by a slash ('/')
          followed by a mask.

In TCP mode, any connection coming from a source matching <source> will cause
the connection to be immediately closed without any log. This allows another
equipment to probe the port and verify that it is still listening, without
forwarding the connection to a remote server.

In HTTP mode, a connection coming from a source matching <source> will be
accepted, the following response will be sent without waiting for a request,
then the connection will be closed : "HTTP/1.0 200 OK". This is normally
enough for any front-end HTTP probe to detect that the service is UP and
running without forwarding the request to a backend server. Note that this
response is sent in raw format, without any transformation. This is important
as it means that it will not be SSL-encrypted on SSL listeners.

Monitor requests are processed very early, just after tcp-request connection
ACLs which are the only ones able to block them. These connections are short
lived and never wait for any data from the client. They cannot be logged, and
it is the intended purpose. They are only used to report HAProxy's health to
an upper component, nothing more. Please note that "monitor fail" rules do
not apply to connections intercepted by "monitor-net".

Last, please note that only one "monitor-net" statement can be specified in
a frontend. If more than one is found, only the last one will be considered.

# addresses .252 and .253 are just probing us.
frontend www
    monitor-net 192.168.0.252/31

Intercept a URI used by external components' monitor requests

<uri>     is the exact URI which we want to intercept to return HAProxy's
          health status instead of forwarding the request.

When an HTTP request referencing <uri> will be received on a frontend,
HAProxy will not forward it nor log it, but instead will return either
"HTTP/1.0 200 OK" or "HTTP/1.0 503 Service unavailable", depending on failure
conditions defined with "monitor fail". This is normally enough for any
front-end HTTP probe to detect that the service is UP and running without
forwarding the request to a backend server. Note that the HTTP method, the
version and all headers are ignored, but the request must at least be valid
at the HTTP level. This keyword may only be used with an HTTP-mode frontend.

Monitor requests are processed very early, just after the request is parsed
and even before any "http-request" or "block" rulesets. The only rulesets
applied before are the tcp-request ones. They cannot be logged either, and it
is the intended purpose. They are only used to report HAProxy's health to an
upper component, nothing more. However, it is possible to add any number of
conditions using "monitor fail" and ACLs so that the result can be adjusted
to whatever check can be imagined (most often the number of available servers
in a backend).

# Use /haproxy_test to report haproxy's status
frontend www
    mode http
    monitor-uri /haproxy_test

Enable or disable early dropping of aborted requests pending in queues.

In presence of very high loads, the servers will take some time to respond.
The per-instance connection queue will inflate, and the response time will
increase respective to the size of the queue times the average per-session
response time. When clients will wait for more than a few seconds, they will
often hit the "STOP" button on their browser, leaving a useless request in
the queue, and slowing down other users, and the servers as well, because the
request will eventually be served, then aborted at the first error
encountered while delivering the response.

As there is no way to distinguish between a full STOP and a simple output
close on the client side, HTTP agents should be conservative and consider
that the client might only have closed its output channel while waiting for
the response. However, this introduces risks of congestion when lots of users
do the same, and is completely useless nowadays because probably no client at
all will close the session while waiting for the response. Some HTTP agents
support this behavior (Squid, Apache, HAProxy), and others do not (TUX, most
hardware-based load balancers). So the probability for a closed input channel
to represent a user hitting the "STOP" button is close to 100%, and the risk
of being the single component to break rare but valid traffic is extremely
low, which adds to the temptation to be able to abort a session early while
still not served and not pollute the servers.

In HAProxy, the user can choose the desired behavior using the option
"abortonclose". By default (without the option) the behavior is HTTP
compliant and aborted requests will be served. But when the option is
specified, a session with an incoming channel closed will be aborted while
it is still possible, either pending in the queue for a connection slot, or
during the connection establishment if the server has not yet acknowledged
the connection request. This considerably reduces the queue size and the load
on saturated servers when users are tempted to click on STOP, which in turn
reduces the response time for other users.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Enable or disable relaxing of HTTP request parsing

By default, HAProxy complies with RFC7230 in terms of message parsing. This
means that invalid characters in header names are not permitted and cause an
error to be returned to the client. This is the desired behavior as such
forbidden characters are essentially used to build attacks exploiting server
weaknesses, and bypass security filtering. Sometimes, a buggy browser or
server will emit invalid header names for whatever reason (configuration,
implementation) and the issue will not be immediately fixed. In such a case,
it is possible to relax HAProxy's header name parser to accept any character
even if that does not make sense, by specifying this option. Similarly, the
list of characters allowed to appear in a URI is well defined by RFC3986, and
chars 0-31, 32 (space), 34 ('"'), 60 ('<'), 62 ('>'), 92 ('\'), 94 ('^'), 96
('`'), 123 ('{'), 124 ('|'), 125 ('}'), 127 (delete) and anything above are
not allowed at all. HAProxy always blocks a number of them (0..32, 127). The
remaining ones are blocked by default unless this option is enabled. This
option also relaxes the test on the HTTP version, it allows HTTP/0.9 requests
to pass through (no version specified) and multiple digits for both the major
and the minor version.

This option should never be enabled by default as it hides application bugs
and open security breaches. It should only be deployed after a problem has
been confirmed.

When this option is enabled, erroneous header names will still be accepted in
requests, but the complete request will be captured in order to permit later
analysis using the "show errors" request on the UNIX stats socket. Similarly,
requests containing invalid chars in the URI part will be logged. Doing this
also helps confirming that the issue has been solved.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Enable or disable relaxing of HTTP response parsing

By default, HAProxy complies with RFC7230 in terms of message parsing. This
means that invalid characters in header names are not permitted and cause an
error to be returned to the client. This is the desired behavior as such
forbidden characters are essentially used to build attacks exploiting server
weaknesses, and bypass security filtering. Sometimes, a buggy browser or
server will emit invalid header names for whatever reason (configuration,
implementation) and the issue will not be immediately fixed. In such a case,
it is possible to relax HAProxy's header name parser to accept any character
even if that does not make sense, by specifying this option. This option also
relaxes the test on the HTTP version format, it allows multiple digits for
both the major and the minor version.

This option should never be enabled by default as it hides application bugs
and open security breaches. It should only be deployed after a problem has
been confirmed.

When this option is enabled, erroneous header names will still be accepted in
responses, but the complete response will be captured in order to permit
later analysis using the "show errors" request on the UNIX stats socket.
Doing this also helps confirming that the issue has been solved.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Use either all backup servers at a time or only the first one

By default, the first operational backup server gets all traffic when normal
servers are all down. Sometimes, it may be preferred to use multiple backups
at once, because one will not be enough. When "option allbackups" is enabled,
the load balancing will be performed among all backup servers when all normal
ones are unavailable. The same load balancing algorithm will be used and the
servers' weights will be respected. Thus, there will not be any priority
order between the backup servers anymore.

This option is mostly used with static server farms dedicated to return a
"sorry" page when an application is completely offline.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Analyze all server responses and block responses with cacheable cookies

Some high-level frameworks set application cookies everywhere and do not
always let enough control to the developer to manage how the responses should
be cached. When a session cookie is returned on a cacheable object, there is a
high risk of session crossing or stealing between users traversing the same
caches. In some situations, it is better to block the response than to let
some sensitive session information go in the wild.

The option "checkcache" enables deep inspection of all server responses for
strict compliance with HTTP specification in terms of cacheability. It
carefully checks "Cache-control", "Pragma" and "Set-cookie" headers in server
response to check if there's a risk of caching a cookie on a client-side
proxy. When this option is enabled, the only responses which can be delivered
to the client are :
  - all those without "Set-Cookie" header;
  - all those with a return code other than 200, 203, 204, 206, 300, 301,
    404, 405, 410, 414, 501, provided that the server has not set a
    "Cache-control: public" header field;
  - all those that result from a request using a method other than GET, HEAD,
    OPTIONS, TRACE, provided that the server has not set a 'Cache-Control:
    public' header field;
  - those with a 'Pragma: no-cache' header
  - those with a 'Cache-control: private' header
  - those with a 'Cache-control: no-store' header
  - those with a 'Cache-control: max-age=0' header
  - those with a 'Cache-control: s-maxage=0' header
  - those with a 'Cache-control: no-cache' header
  - those with a 'Cache-control: no-cache="set-cookie"' header
  - those with a 'Cache-control: no-cache="set-cookie,' header
    (allowing other fields after set-cookie)

If a response doesn't respect these requirements, then it will be blocked
just as if it was from an "rspdeny" filter, with an "HTTP 502 bad gateway".
The session state shows "PH--" meaning that the proxy blocked the response
during headers processing. Additionally, an alert will be sent in the logs so
that admins are informed that there's something to be fixed.

Due to the high impact on the application, the application should be tested
in depth with the option enabled before going to production. It is also a
good practice to always activate it during tests, even if it is not used in
production, as it will report potentially dangerous application behaviors.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Enable or disable the sending of TCP keepalive packets on the client side

When there is a firewall or any session-aware component between a client and
a server, and when the protocol involves very long sessions with long idle
periods (e.g. remote desktops), there is a risk that one of the intermediate
components decides to expire a session which has remained idle for too long.

Enabling socket-level TCP keep-alives makes the system regularly send packets
to the other end of the connection, leaving it active. The delay between
keep-alive probes is controlled by the system only and depends both on the
operating system and its tuning parameters.

It is important to understand that keep-alive packets are neither emitted nor
received at the application level. It is only the network stacks which sees
them. For this reason, even if one side of the proxy already uses keep-alives
to maintain its connection alive, those keep-alive packets will not be
forwarded to the other side of the proxy.

Please note that this has nothing to do with HTTP keep-alive.

Using option "clitcpka" enables the emission of TCP keep-alive probes on the
client side of a connection, which should help when session expirations are
noticed between HAProxy and a client.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Enable continuous traffic statistics updates

By default, counters used for statistics calculation are incremented
only when a session finishes. It works quite well when serving small
objects, but with big ones (for example large images or archives) or
with A/V streaming, a graph generated from haproxy counters looks like
a hedgehog. With this option enabled counters get incremented frequently
along the session, typically every 5 seconds, which is often enough to
produce clean graphs. Recounting touches a hotpath directly so it is not
not enabled by default, as it can cause a lot of wakeups for very large
session counts and cause a small performance drop.

Enable or disable logging of normal, successful connections

There are large sites dealing with several thousand connections per second
and for which logging is a major pain. Some of them are even forced to turn
logs off and cannot debug production issues. Setting this option ensures that
normal connections, those which experience no error, no timeout, no retry nor
redispatch, will not be logged. This leaves disk space for anomalies. In HTTP
mode, the response status code is checked and return codes 5xx will still be
logged.

It is strongly discouraged to use this option as most of the time, the key to
complex issues is in the normal logs which will not be logged here. If you
need to separate logs, see the "log-separate-errors" option instead.

Enable or disable logging of null connections

In certain environments, there are components which will regularly connect to
various systems to ensure that they are still alive. It can be the case from
another load balancer as well as from monitoring systems. By default, even a
simple port probe or scan will produce a log. If those connections pollute
the logs too much, it is possible to enable option "dontlognull" to indicate
that a connection on which no data has been transferred will not be logged,
which typically corresponds to those probes. Note that errors will still be
returned to the client and accounted for in the stats. If this is not what is
desired, option http-ignore-probes can be used instead.

It is generally recommended not to use this option in uncontrolled
environments (e.g. internet), otherwise scans and other malicious activities
would not be logged.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

This is an alias for "option httpclose". Thus this option is deprecated.

Enable insertion of the X-Forwarded-For header to requests sent to servers

<network> is an optional argument used to disable this option for sources
          matching <network>
<name>    an optional argument to specify a different "X-Forwarded-For"
          header name.

Since HAProxy works in reverse-proxy mode, the servers see its IP address as
their client address. This is sometimes annoying when the client's IP address
is expected in server logs. To solve this problem, the well-known HTTP header
"X-Forwarded-For" may be added by HAProxy to all requests sent to the server.
This header contains a value representing the client's IP address. Since this
header is always appended at the end of the existing header list, the server
must be configured to always use the last occurrence of this header only. See
the server's manual to find how to enable use of this standard header. Note
that only the last occurrence of the header must be used, since it is really
possible that the client has already brought one.

The keyword "header" may be used to supply a different header name to replace
the default "X-Forwarded-For". This can be useful where you might already
have a "X-Forwarded-For" header from a different application (e.g. stunnel),
and you need preserve it. Also if your backend server doesn't use the
"X-Forwarded-For" header and requires different one (e.g. Zeus Web Servers
require "X-Cluster-Client-IP").

Sometimes, a same HAProxy instance may be shared between a direct client
access and a reverse-proxy access (for instance when an SSL reverse-proxy is
used to decrypt HTTPS traffic). It is possible to disable the addition of the
header for a known source address or network by adding the "except" keyword
followed by the network address. In this case, any source IP matching the
network will not cause an addition of this header. Most common uses are with
private networks or 127.0.0.1.

Alternatively, the keyword "if-none" states that the header will only be
added if it is not present. This should only be used in perfectly trusted
environment, as this might cause a security issue if headers reaching haproxy
are under the control of the end-user.

This option may be specified either in the frontend or in the backend. If at
least one of them uses it, the header will be added. Note that the backend's
setting of the header subargument takes precedence over the frontend's if
both are defined. In the case of the "if-none" argument, if at least one of
the frontend or the backend does not specify it, it wants the addition to be
mandatory, so it wins.

# Public HTTP address also used by stunnel on the same machine
frontend www
    mode http
    option forwardfor except 127.0.0.1  # stunnel already adds the header

# Those servers want the IP Address in X-Client
backend www
    mode http
    option forwardfor header X-Client

Enable or disable waiting for whole HTTP request body before proceeding

It is sometimes desirable to wait for the body of an HTTP request before
taking a decision. This is what is being done by "balance url_param" for
example. The first use case is to buffer requests from slow clients before
connecting to the server. Another use case consists in taking the routing
decision based on the request body's contents. This option placed in a
frontend or backend forces the HTTP processing to wait until either the whole
body is received, or the request buffer is full, or the first chunk is
complete in case of chunked encoding. It can have undesired side effects with
some applications abusing HTTP by expecting unbuffered transmissions between
the frontend and the backend, so this should definitely not be used by
default.

Enable or disable logging of null connections and request timeouts

Recently some browsers started to implement a "pre-connect" feature
consisting in speculatively connecting to some recently visited web sites
just in case the user would like to visit them. This results in many
connections being established to web sites, which end up in 408 Request
Timeout if the timeout strikes first, or 400 Bad Request when the browser
decides to close them first. These ones pollute the log and feed the error
counters. There was already "option dontlognull" but it's insufficient in
this case. Instead, this option does the following things :
   - prevent any 400/408 message from being sent to the client if nothing
     was received over a connection before it was closed;
   - prevent any log from being emitted in this situation;
   - prevent any error counter from being incremented

That way the empty connection is silently ignored. Note that it is better
not to use this unless it is clear that it is needed, because it will hide
real problems. The most common reason for not receiving a request and seeing
a 408 is due to an MTU inconsistency between the client and an intermediary
element such as a VPN, which blocks too large packets. These issues are
generally seen with POST requests as well as GET with large cookies. The logs
are often the only way to detect them.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Enable or disable HTTP keep-alive from client to server

By default HAProxy operates in keep-alive mode with regards to persistent
connections: for each connection it processes each request and response, and
leaves the connection idle on both sides between the end of a response and
the start of a new request. This mode may be changed by several options such
as "option http-server-close", "option httpclose" or "option http-tunnel".
This option allows to set back the keep-alive mode, which can be useful when
another mode was used in a defaults section.

Setting "option http-keep-alive" enables HTTP keep-alive mode on the client-
and server- sides. This provides the lowest latency on the client side (slow
network) and the fastest session reuse on the server side at the expense
of maintaining idle connections to the servers. In general, it is possible
with this option to achieve approximately twice the request rate that the
"http-server-close" option achieves on small objects. There are mainly two
situations where this option may be useful :

  - when the server is non-HTTP compliant and authenticates the connection
    instead of requests (e.g. NTLM authentication)

  - when the cost of establishing the connection to the server is significant
    compared to the cost of retrieving the associated object from the server.

This last case can happen when the server is a fast static server of cache.
In this case, the server will need to be properly tuned to support high enough
connection counts because connections will last until the client sends another
request.

If the client request has to go to another backend or another server due to
content switching or the load balancing algorithm, the idle connection will
immediately be closed and a new one re-opened. Option "prefer-last-server" is
available to try optimize server selection so that if the server currently
attached to an idle connection is usable, it will be used.

At the moment, logs will not indicate whether requests came from the same
session or not. The accept date reported in the logs corresponds to the end
of the previous request, and the request time corresponds to the time spent
waiting for a new request. The keep-alive request time is still bound to the
timeout defined by "timeout http-keep-alive" or "timeout http-request" if
not set.

This option disables and replaces any previous "option httpclose", "option
http-server-close" or "option http-tunnel". When backend and frontend options
differ, all of these 4 options have precedence over "option http-keep-alive".

Instruct the system to favor low interactive delays over performance in HTTP

In HTTP, each payload is unidirectional and has no notion of interactivity.
Any agent is expected to queue data somewhat for a reasonably low delay.
There are some very rare server-to-server applications that abuse the HTTP
protocol and expect the payload phase to be highly interactive, with many
interleaved data chunks in both directions within a single request. This is
absolutely not supported by the HTTP specification and will not work across
most proxies or servers. When such applications attempt to do this through
haproxy, it works but they will experience high delays due to the network
optimizations which favor performance by instructing the system to wait for
enough data to be available in order to only send full packets. Typical
delays are around 200 ms per round trip. Note that this only happens with
abnormal uses. Normal uses such as CONNECT requests nor WebSockets are not
affected.

When "option http-no-delay" is present in either the frontend or the backend
used by a connection, all such optimizations will be disabled in order to
make the exchanges as fast as possible. Of course this offers no guarantee on
the functionality, as it may break at any other place. But if it works via
HAProxy, it will work as fast as possible. This option should never be used
by default, and should never be used at all unless such a buggy application
is discovered. The impact of using this option is an increase of bandwidth
usage and CPU usage, which may significantly lower performance in high
latency environments.

Define whether haproxy will announce keepalive to the server or not

When running with "option http-server-close" or "option httpclose", haproxy
adds a "Connection: close" header to the request forwarded to the server.
Unfortunately, when some servers see this header, they automatically refrain
from using the chunked encoding for responses of unknown length, while this
is totally unrelated. The immediate effect is that this prevents haproxy from
maintaining the client connection alive. A second effect is that a client or
a cache could receive an incomplete response without being aware of it, and
consider the response complete.

By setting "option http-pretend-keepalive", haproxy will make the server
believe it will keep the connection alive. The server will then not fall back
to the abnormal undesired above. When haproxy gets the whole response, it
will close the connection with the server just as it would do with the
"option httpclose". That way the client gets a normal response and the
connection is correctly closed on the server side.

It is recommended not to enable this option by default, because most servers
will more efficiently close the connection themselves after the last packet,
and release its buffers slightly earlier. Also, the added packet on the
network could slightly reduce the overall peak performance. However it is
worth noting that when this option is enabled, haproxy will have slightly
less work to do. So if haproxy is the bottleneck on the whole architecture,
enabling this option might save a few CPU cycles.

This option may be set in backend and listen sections. Using it in a frontend
section will be ignored and a warning will be reported during startup. It is
a backend related option, so there is no real reason to set it on a
frontend. This option may be combined with "option httpclose", which will
cause keepalive to be announced to the server and close to be announced to
the client. This practice is discouraged though.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Enable or disable HTTP connection closing on the server side

By default HAProxy operates in keep-alive mode with regards to persistent
connections: for each connection it processes each request and response, and
leaves the connection idle on both sides between the end of a response and
the start of a new request. This mode may be changed by several options such
as "option http-server-close", "option httpclose" or "option http-tunnel".
Setting "option http-server-close" enables HTTP connection-close mode on the
server side while keeping the ability to support HTTP keep-alive and
pipelining on the client side. This provides the lowest latency on the client
side (slow network) and the fastest session reuse on the server side to save
server resources, similarly to "option httpclose".  It also permits
non-keepalive capable servers to be served in keep-alive mode to the clients
if they conform to the requirements of RFC7230. Please note that some servers
do not always conform to those requirements when they see "Connection: close"
in the request. The effect will be that keep-alive will never be used. A
workaround consists in enabling "option http-pretend-keepalive".

At the moment, logs will not indicate whether requests came from the same
session or not. The accept date reported in the logs corresponds to the end
of the previous request, and the request time corresponds to the time spent
waiting for a new request. The keep-alive request time is still bound to the
timeout defined by "timeout http-keep-alive" or "timeout http-request" if
not set.

This option may be set both in a frontend and in a backend. It is enabled if
at least one of the frontend or backend holding a connection has it enabled.
It disables and replaces any previous "option httpclose", "option http-tunnel"
or "option http-keep-alive". Please check section 4 ("Proxies") to see how
this option combines with others when frontend and backend options differ.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Disable or enable HTTP connection processing after first transaction.

Warning : Because it cannot work in HTTP/2, this option is deprecated and it
is only supported on legacy HTTP frontends. In HTX, it is ignored and a
warning is emitted during HAProxy startup.

By default HAProxy operates in keep-alive mode with regards to persistent
connections: for each connection it processes each request and response, and
leaves the connection idle on both sides between the end of a response and
the start of a new request. This mode may be changed by several options such
as "option http-server-close", "option httpclose" or "option http-tunnel".

Option "http-tunnel" disables any HTTP processing past the first request and
the first response. This is the mode which was used by default in versions
1.0 to 1.5-dev21. It is the mode with the lowest processing overhead, which
is normally not needed anymore unless in very specific cases such as when
using an in-house protocol that looks like HTTP but is not compatible, or
just to log one request per client in order to reduce log size. Note that
everything which works at the HTTP level, including header parsing/addition,
cookie processing or content switching will only work for the first request
and will be ignored after the first response.

This option may be set on frontend and listen sections. Using it on a backend
section will be ignored and a warning will be reported during the startup. It
is a frontend related option, so there is no real reason to set it on a
backend.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Make use of non-standard Proxy-Connection header instead of Connection

While RFC7230 explicitly states that HTTP/1.1 agents must use the
Connection header to indicate their wish of persistent or non-persistent
connections, both browsers and proxies ignore this header for proxied
connections and make use of the undocumented, non-standard Proxy-Connection
header instead. The issue begins when trying to put a load balancer between
browsers and such proxies, because there will be a difference between what
haproxy understands and what the client and the proxy agree on.

By setting this option in a frontend, haproxy can automatically switch to use
that non-standard header if it sees proxied requests. A proxied request is
defined here as one where the URI begins with neither a '/' nor a '*'. This
is incompatible with the HTTP tunnel mode. Note that this option can only be
specified in a frontend and will affect the request along its whole life.

Also, when this option is set, a request which requires authentication will
automatically switch to use proxy authentication headers if it is itself a
proxied request. That makes it possible to check or enforce authentication in
front of an existing proxy.

This option should normally never be used, except in front of a proxy.

Switch to the new HTX internal representation for HTTP protocol elements

By default, the HTTP protocol is processed as-is. Inserting, deleting, or
modifying a header field requires to rewrite the affected part in the buffer
and to move the buffer's tail accordingly. Since this principle has deep
roots in haproxy, the HTTP/2 protocol is converted to HTTP/1.1 before being
processed this way. It also results in the inability to establish HTTP/2
connections to servers because of the loss of HTTP/2 semantics in the HTTP/1
representation.

HTX is the name of a totally new native internal representation for the HTTP
protocol, that is agnostic to the version and aims at preserving semantics
all along the chain. It relies on a fast parsing, tokenizing and indexing of
the protocol elements so that no more memory moves are necessary and that
most elements are directly accessed. This mechanism is still limited to the
most basic operations (no compression, filters, Lua, applets, cache, etc).
But it supports using either HTTP/1 or HTTP/2 on any side regardless of the
other side's version.

This option indicates that HTX needs to be used. It will cause errors to be
emitted if incompatible features are used, but will allow H2 to be selected
as a server protocol. It is recommended to use this option on new reasonably
simple configurations, but since the feature still has incomplete functional
coverage, it is not enabled by default.

Enable HTTP protocol to check on the servers health

<method>  is the optional HTTP method used with the requests. When not set,
          the "OPTIONS" method is used, as it generally requires low server
          processing and is easy to filter out from the logs. Any method
          may be used, though it is not recommended to invent non-standard
          ones.

<uri>     is the URI referenced in the HTTP requests. It defaults to " / "
          which is accessible by default on almost any server, but may be
          changed to any other URI. Query strings are permitted.

<version> is the optional HTTP version string. It defaults to "HTTP/1.0"
          but some servers might behave incorrectly in HTTP 1.0, so turning
          it to HTTP/1.1 may sometimes help. Note that the Host field is
          mandatory in HTTP/1.1, use "http-check send" directive to add it.

By default, server health checks only consist in trying to establish a TCP
connection. When "option httpchk" is specified, a complete HTTP request is
sent once the TCP connection is established, and responses 2xx and 3xx are
considered valid, while all other ones indicate a server failure, including
the lack of any response.

The port and interval are specified in the server configuration.

This option does not necessarily require an HTTP backend, it also works with
plain TCP backends. This is particularly useful to check simple scripts bound
to some dedicated ports using the inetd daemon.

Note : For a while, there was no way to add headers or body in the request
       used for HTTP health checks. So a workaround was to hide it at the end
       of the version string with a "\r\n" after the version. It is now
       deprecated. The directive "http-check send" must be used instead.

# Relay HTTPS traffic to Apache instance and check service availability
# using HTTP request "OPTIONS * HTTP/1.1" on port 80.
backend https_relay
    mode tcp
    option httpchk OPTIONS * HTTP/1.1
    http-check send hdr Host www
    server apache1 192.168.1.1:443 check port 80

Enable or disable HTTP connection closing

By default HAProxy operates in keep-alive mode with regards to persistent
connections: for each connection it processes each request and response, and
leaves the connection idle on both sides between the end of a response and
the start of a new request. This mode may be changed by several options such
as "option http-server-close", "option httpclose" or "option http-tunnel".

If "option httpclose" is set, HAProxy will close connections with the server
and the client as soon as the request and the response are received. It will
alos check if a "Connection: close" header is already set in each direction,
and will add one if missing. Any "Connection" header different from "close"
will also be removed.

This option may also be combined with "option http-pretend-keepalive", which
will disable sending of the "Connection: close" header, but will still cause
the connection to be closed once the whole response is received.

This option may be set both in a frontend and in a backend. It is enabled if
at least one of the frontend or backend holding a connection has it enabled.
It disables and replaces any previous "option http-server-close",
"option http-keep-alive" or "option http-tunnel". Please check section 4
("Proxies") to see how this option combines with others when frontend and
backend options differ.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Enable logging of HTTP request, session state and timers

clf       if the "clf" argument is added, then the output format will be
          the CLF format instead of HAProxy's default HTTP format. You can
          use this when you need to feed HAProxy's logs through a specific
          log analyzer which only support the CLF format and which is not
          extensible.

By default, the log output format is very poor, as it only contains the
source and destination addresses, and the instance name. By specifying
"option httplog", each log line turns into a much richer format including,
but not limited to, the HTTP request, the connection timers, the session
status, the connections numbers, the captured headers and cookies, the
frontend, backend and server name, and of course the source address and
ports.

Specifying only "option httplog" will automatically clear the 'clf' mode
if it was set by default.

"option httplog" overrides any previous "log-format" directive.

Enable or disable plain HTTP proxy mode

It sometimes happens that people need a pure HTTP proxy which understands
basic proxy requests without caching nor any fancy feature. In this case,
it may be worth setting up an HAProxy instance with the "option http_proxy"
set. In this mode, no server is declared, and the connection is forwarded to
the IP address and port found in the URL after the "http://" scheme.

No host address resolution is performed, so this only works when pure IP
addresses are passed. Since this option's usage perimeter is rather limited,
it will probably be used only by experts who know they need exactly it. This
is incompatible with the HTTP tunnel mode.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

# this backend understands HTTP proxy requests and forwards them directly.
backend direct_forward
    option httpclose
    option http_proxy

Enable or disable independent timeout processing for both directions

By default, when data is sent over a socket, both the write timeout and the
read timeout for that socket are refreshed, because we consider that there is
activity on that socket, and we have no other means of guessing if we should
receive data or not.

While this default behavior is desirable for almost all applications, there
exists a situation where it is desirable to disable it, and only refresh the
read timeout if there are incoming data. This happens on sessions with large
timeouts and low amounts of exchanged data such as telnet session. If the
server suddenly disappears, the output data accumulates in the system's
socket buffers, both timeouts are correctly refreshed, and there is no way
to know the server does not receive them, so we don't timeout. However, when
the underlying protocol always echoes sent data, it would be enough by itself
to detect the issue using the read timeout. Note that this problem does not
happen with more verbose protocols because data won't accumulate long in the
socket buffers.

When this option is set on the frontend, it will disable read timeout updates
on data sent to the client. There probably is little use of this case. When
the option is set on the backend, it will disable read timeout updates on
data sent to the server. Doing so will typically break large HTTP posts from
slow lines, so use it with caution.

Note: older versions used to call this setting "option independant-streams"
      with a spelling mistake. This spelling is still supported but
      deprecated.

Use LDAPv3 health checks for server testing

It is possible to test that the server correctly talks LDAPv3 instead of just
testing that it accepts the TCP connection. When this option is set, an
LDAPv3 anonymous simple bind message is sent to the server, and the response
is analyzed to find an LDAPv3 bind response message.

The server is considered valid only when the LDAP response contains success
resultCode (http://tools.ietf.org/html/rfc4511#section-4.1.9).

Logging of bind requests is server dependent see your documentation how to
configure it.

option ldap-check

Use external processes for server health checks

It is possible to test the health of a server using an external command.
This is achieved by running the executable set using "external-check
command".

Requires the "external-check" global to be set.

Enable or disable logging of health checks status updates

By default, failed health check are logged if server is UP and successful
health checks are logged if server is DOWN, so the amount of additional
information is limited.

When this option is enabled, any change of the health check status or to
the server's health will be logged, so that it becomes possible to know
that a server was failing occasional checks before crashing, or exactly when
it failed to respond a valid HTTP status, then when the port started to
reject connections, then when the server stopped responding at all.

Note that status changes not caused by health checks (e.g. enable/disable on
the CLI) are intentionally not logged by this option.

Change log level for non-completely successful connections

Sometimes looking for errors in logs is not easy. This option makes haproxy
raise the level of logs containing potentially interesting information such
as errors, timeouts, retries, redispatches, or HTTP status codes 5xx. The
level changes from "info" to "err". This makes it possible to log them
separately to a different file with most syslog daemons. Be careful not to
remove them from the original file, otherwise you would lose ordering which
provides very important information.

Using this option, large sites dealing with several thousand connections per
second may log normal traffic to a rotating buffer and only archive smaller
error logs.

Enable or disable early logging.

By default, logs are emitted when all the log format variables and sample
fetches used in the definition of the log-format string return a value, or
when the session is terminated. This allows the built in log-format strings
to account for the transfer time, or the number of bytes in log messages.

When handling long lived connections such as large file transfers or RDP,
it may take a while for the request or connection to appear in the logs.
Using "option logasap", the log message is created as soon as the server
connection is established in mode tcp, or as soon as the server sends the
complete headers in mode http. Missing information in the logs will be the
total number of bytes which will only indicate the amount of data transfered
before the message was created and the total time which will not take the
remainder of the connection life or transfer time into account. For the case
of HTTP, it is good practice to capture the Content-Length response header
so that the logs at least indicate how many bytes are expected to be
transfered.

  listen http_proxy 0.0.0.0:80
      mode http
      option httplog
      option logasap
      log 192.168.2.200 local3

>>> Feb  6 12:14:14 localhost \
      haproxy[14389]: 10.0.1.2:33317 [06/Feb/2009:12:14:14.655] http-in \
      static/srv1 9/10/7/14/+30 200 +243 - - ---- 3/1/1/1/0 1/0 \
      "GET /image.iso HTTP/1.0"

Use MySQL health checks for server testing

<username> This is the username which will be used when connecting to MySQL
           server.
post-41    Send post v4.1 client compatible checks

If you specify a username, the check consists of sending two MySQL packet,
one Client Authentication packet, and one QUIT packet, to correctly close
MySQL session. We then parse the MySQL Handshake Initialization packet and/or
Error packet. It is a basic but useful test which does not produce error nor
aborted connect on the server. However, it requires adding an authorization
in the MySQL table, like this :

    USE mysql;
    INSERT INTO user (Host,User) values ('<ip_of_haproxy>','<username>');
    FLUSH PRIVILEGES;

If you don't specify a username (it is deprecated and not recommended), the
check only consists in parsing the Mysql Handshake Initialization packet or
Error packet, we don't send anything in this mode. It was reported that it
can generate lockout if check is too frequent and/or if there is not enough
traffic. In fact, you need in this case to check MySQL "max_connect_errors"
value as if a connection is established successfully within fewer than MySQL
"max_connect_errors" attempts after a previous connection was interrupted,
the error count for the host is cleared to zero. If HAProxy's server get
blocked, the "FLUSH HOSTS" statement is the only way to unblock it.

Remember that this does not check database presence nor database consistency.
To do this, you can use an external check with xinetd for example.

The check requires MySQL >=3.22, for older version, please use TCP check.

Most often, an incoming MySQL server needs to see the client's IP address for
various purposes, including IP privilege matching and connection logging.
When possible, it is often wise to masquerade the client's IP address when
connecting to the server using the "usesrc" argument of the "source" keyword,
which requires the transparent proxy feature to be compiled in, and the MySQL
server to route the client via the machine hosting haproxy.

Enable or disable immediate session resource cleaning after close

When clients or servers abort connections in a dirty way (e.g. they are
physically disconnected), the session timeouts triggers and the session is
closed. But it will remain in FIN_WAIT1 state for some time in the system,
using some resources and possibly limiting the ability to establish newer
connections.

When this happens, it is possible to activate "option nolinger" which forces
the system to immediately remove any socket's pending data on close. Thus,
the session is instantly purged from the system's tables. This usually has
side effects such as increased number of TCP resets due to old retransmits
getting immediately rejected. Some firewalls may sometimes complain about
this too.

For this reason, it is not recommended to use this option when not absolutely
needed. You know that you need it when you have thousands of FIN_WAIT1
sessions on your system (TIME_WAIT ones do not count).

This option may be used both on frontends and backends, depending on the side
where it is required. Use it on the frontend for clients, and on the backend
for servers.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Enable insertion of the X-Original-To header to requests sent to servers

<network> is an optional argument used to disable this option for sources
          matching <network>
<name>    an optional argument to specify a different "X-Original-To"
          header name.

Since HAProxy can work in transparent mode, every request from a client can
be redirected to the proxy and HAProxy itself can proxy every request to a
complex SQUID environment and the destination host from SO_ORIGINAL_DST will
be lost. This is annoying when you want access rules based on destination ip
addresses. To solve this problem, a new HTTP header "X-Original-To" may be
added by HAProxy to all requests sent to the server. This header contains a
value representing the original destination IP address. Since this must be
configured to always use the last occurrence of this header only. Note that
only the last occurrence of the header must be used, since it is really
possible that the client has already brought one.

The keyword "header" may be used to supply a different header name to replace
the default "X-Original-To". This can be useful where you might already
have a "X-Original-To" header from a different application, and you need
preserve it. Also if your backend server doesn't use the "X-Original-To"
header and requires different one.

Sometimes, a same HAProxy instance may be shared between a direct client
access and a reverse-proxy access (for instance when an SSL reverse-proxy is
used to decrypt HTTPS traffic). It is possible to disable the addition of the
header for a known source address or network by adding the "except" keyword
followed by the network address. In this case, any source IP matching the
network will not cause an addition of this header. Most common uses are with
private networks or 127.0.0.1.

This option may be specified either in the frontend or in the backend. If at
least one of them uses it, the header will be added. Note that the backend's
setting of the header subargument takes precedence over the frontend's if
both are defined.

# Original Destination address
frontend www
    mode http
    option originalto except 127.0.0.1

# Those servers want the IP Address in X-Client-Dst
backend www
    mode http
    option originalto header X-Client-Dst

Enable or disable forced persistence on down servers

When an HTTP request reaches a backend with a cookie which references a dead
server, by default it is redispatched to another server. It is possible to
force the request to be sent to the dead server first using "option persist"
if absolutely needed. A common use case is when servers are under extreme
load and spend their time flapping. In this case, the users would still be
directed to the server they opened the session on, in the hope they would be
correctly served. It is recommended to use "option redispatch" in conjunction
with this option so that in the event it would not be possible to connect to
the server at all (server definitely dead), the client would finally be
redirected to another valid server.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Use PostgreSQL health checks for server testing

<username> This is the username which will be used when connecting to
           PostgreSQL server.

The check sends a PostgreSQL StartupMessage and waits for either
Authentication request or ErrorResponse message. It is a basic but useful
test which does not produce error nor aborted connect on the server.
This check is identical with the "mysql-check".

Allow multiple load balanced requests to remain on the same server

When the load balancing algorithm in use is not deterministic, and a previous
request was sent to a server to which haproxy still holds a connection, it is
sometimes desirable that subsequent requests on a same session go to the same
server as much as possible. Note that this is different from persistence, as
we only indicate a preference which haproxy tries to apply without any form
of warranty. The real use is for keep-alive connections sent to servers. When
this option is used, haproxy will try to reuse the same connection that is
attached to the server instead of rebalancing to another server, causing a
close of the connection. This can make sense for static file servers. It does
not make much sense to use this in combination with hashing algorithms. Note,
haproxy already automatically tries to stick to a server which sends a 401 or
to a proxy which sends a 407 (authentication required), when the load
balancing algorithm is not deterministic. This is mandatory for use with the
broken NTLM authentication challenge, and significantly helps in
troubleshooting some faulty applications. Option prefer-last-server might be
desirable in these environments as well, to avoid redistributing the traffic
after every other response.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Enable or disable session redistribution in case of connection failure

<interval> The optional integer value that controls how often redispatches
           occur when retrying connections. Positive value P indicates a
           redispatch is desired on every Pth retry, and negative value
           N indicate a redispatch is desired on the Nth retry prior to the
           last retry. For example, the default of -1 preserves the
           historical behavior of redispatching on the last retry, a
           positive value of 1 would indicate a redispatch on every retry,
           and a positive value of 3 would indicate a redispatch on every
           third retry. You can disable redispatches with a value of 0.

In HTTP mode, if a server designated by a cookie is down, clients may
definitely stick to it because they cannot flush the cookie, so they will not
be able to access the service anymore.

Specifying "option redispatch" will allow the proxy to break cookie or
consistent hash based persistence and redistribute them to a working server.

It also allows to retry connections to another server in case of multiple
connection failures. Of course, it requires having "retries" set to a nonzero
value.

This form is the preferred form, which replaces both the "redispatch" and
"redisp" keywords.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Use redis health checks for server testing

It is possible to test that the server correctly talks REDIS protocol instead
of just testing that it accepts the TCP connection. When this option is set,
a PING redis command is sent to the server, and the response is analyzed to
find the "+PONG" response message.

option redis-check

Use SMTP health checks for server testing

<hello>   is an optional argument. It is the "hello" command to use. It can
          be either "HELO" (for SMTP) or "EHLO" (for ESMTP). All other
          values will be turned into the default command ("HELO").

<domain>  is the domain name to present to the server. It may only be
          specified (and is mandatory) if the hello command has been
          specified. By default, "localhost" is used.

When "option smtpchk" is set, the health checks will consist in TCP
connections followed by an SMTP command. By default, this command is
"HELO localhost". The server's return code is analyzed and only return codes
starting with a "2" will be considered as valid. All other responses,
including a lack of response will constitute an error and will indicate a
dead server.

This test is meant to be used with SMTP servers or relays. Depending on the
request, it is possible that some servers do not log each connection attempt,
so you may want to experiment to improve the behavior. Using telnet on port
25 is often easier than adjusting the configuration.

Most often, an incoming SMTP server needs to see the client's IP address for
various purposes, including spam filtering, anti-spoofing and logging. When
possible, it is often wise to masquerade the client's IP address when
connecting to the server using the "usesrc" argument of the "source" keyword,
which requires the transparent proxy feature to be compiled in.

option smtpchk HELO mydomain.org

Enable or disable collecting & providing separate statistics for each socket.

Enable or disable automatic kernel acceleration on sockets in both directions

When this option is enabled either on a frontend or on a backend, haproxy
will automatically evaluate the opportunity to use kernel tcp splicing to
forward data between the client and the server, in either direction. HAProxy
uses heuristics to estimate if kernel splicing might improve performance or
not. Both directions are handled independently. Note that the heuristics used
are not much aggressive in order to limit excessive use of splicing. This
option requires splicing to be enabled at compile time, and may be globally
disabled with the global option "nosplice". Since splice uses pipes, using it
requires that there are enough spare pipes.

Important note: kernel-based TCP splicing is a Linux-specific feature which
first appeared in kernel 2.6.25. It offers kernel-based acceleration to
transfer data between sockets without copying these data to user-space, thus
providing noticeable performance gains and CPU cycles savings. Since many
early implementations are buggy, corrupt data and/or are inefficient, this
feature is not enabled by default, and it should be used with extreme care.
While it is not possible to detect the correctness of an implementation,
2.6.29 is the first version offering a properly working implementation. In
case of doubt, splicing may be globally disabled using the global "nosplice"
keyword.

option splice-auto

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Enable or disable automatic kernel acceleration on sockets for requests

When this option is enabled either on a frontend or on a backend, haproxy
will use kernel tcp splicing whenever possible to forward data going from
the client to the server. It might still use the recv/send scheme if there
are no spare pipes left. This option requires splicing to be enabled at
compile time, and may be globally disabled with the global option "nosplice".
Since splice uses pipes, using it requires that there are enough spare pipes.

Important note: see "option splice-auto" for usage limitations.

option splice-request

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Enable or disable automatic kernel acceleration on sockets for responses

When this option is enabled either on a frontend or on a backend, haproxy
will use kernel tcp splicing whenever possible to forward data going from
the server to the client. It might still use the recv/send scheme if there
are no spare pipes left. This option requires splicing to be enabled at
compile time, and may be globally disabled with the global option "nosplice".
Since splice uses pipes, using it requires that there are enough spare pipes.

Important note: see "option splice-auto" for usage limitations.

option splice-response

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Use SPOP health checks for server testing

It is possible to test that the server correctly talks SPOP protocol instead
of just testing that it accepts the TCP connection. When this option is set,
a HELLO handshake is performed between HAProxy and the server, and the
response is analyzed to check no error is reported.

option spop-check

Enable or disable the sending of TCP keepalive packets on the server side

When there is a firewall or any session-aware component between a client and
a server, and when the protocol involves very long sessions with long idle
periods (e.g. remote desktops), there is a risk that one of the intermediate
components decides to expire a session which has remained idle for too long.

Enabling socket-level TCP keep-alives makes the system regularly send packets
to the other end of the connection, leaving it active. The delay between
keep-alive probes is controlled by the system only and depends both on the
operating system and its tuning parameters.

It is important to understand that keep-alive packets are neither emitted nor
received at the application level. It is only the network stacks which sees
them. For this reason, even if one side of the proxy already uses keep-alives
to maintain its connection alive, those keep-alive packets will not be
forwarded to the other side of the proxy.

Please note that this has nothing to do with HTTP keep-alive.

Using option "srvtcpka" enables the emission of TCP keep-alive probes on the
server side of a connection, which should help when session expirations are
noticed between HAProxy and a server.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Use SSLv3 client hello health checks for server testing

When some SSL-based protocols are relayed in TCP mode through HAProxy, it is
possible to test that the server correctly talks SSL instead of just testing
that it accepts the TCP connection. When "option ssl-hello-chk" is set, pure
SSLv3 client hello messages are sent once the connection is established to
the server, and the response is analyzed to find an SSL server hello message.
The server is considered valid only when the response contains this server
hello message.

All servers tested till there correctly reply to SSLv3 client hello messages,
and most servers tested do not even log the requests containing only hello
messages, which is appreciable.

Note that this check works even when SSL support was not built into haproxy
because it forges the SSL message. When SSL support is available, it is best
to use native SSL health checks instead of this one.

Perform health checks using tcp-check send/expect sequences

This health check method is intended to be combined with "tcp-check" command
lists in order to support send/expect types of health check sequences.

TCP checks currently support 4 modes of operations :
  - no "tcp-check" directive : the health check only consists in a connection
    attempt, which remains the default mode.

  - "tcp-check send" or "tcp-check send-binary" only is mentioned : this is
    used to send a string along with a connection opening. With some
    protocols, it helps sending a "QUIT" message for example that prevents
    the server from logging a connection error for each health check. The
    check result will still be based on the ability to open the connection
    only.

  - "tcp-check expect" only is mentioned : this is used to test a banner.
    The connection is opened and haproxy waits for the server to present some
    contents which must validate some rules. The check result will be based
    on the matching between the contents and the rules. This is suited for
    POP, IMAP, SMTP, FTP, SSH, TELNET.

  - both "tcp-check send" and "tcp-check expect" are mentioned : this is
    used to test a hello-type protocol. HAProxy sends a message, the server
    responds and its response is analyzed. the check result will be based on
    the matching between the response contents and the rules. This is often
    suited for protocols which require a binding or a request/response model.
    LDAP, MySQL, Redis and SSL are example of such protocols, though they
    already all have their dedicated checks with a deeper understanding of
    the respective protocols.
    In this mode, many questions may be sent and many answers may be
    analyzed.

  A fifth mode can be used to insert comments in different steps of the
  script.

  For each tcp-check rule you create, you can add a "comment" directive,
  followed by a string. This string will be reported in the log and stderr
  in debug mode. It is useful to make user-friendly error reporting.
  The "comment" is of course optional.

# perform a POP check (analyze only server's banner)
option tcp-check
tcp-check expect string +OK\ POP3\ ready comment POP\ protocol

# perform an IMAP check (analyze only server's banner)
option tcp-check
tcp-check expect string *\ OK\ IMAP4\ ready comment IMAP\ protocol

# look for the redis master server after ensuring it speaks well
# redis protocol, then it exits properly.
# (send a command then analyze the response 3 times)
option tcp-check
tcp-check comment PING\ phase
tcp-check send PING\r\n
tcp-check expect string +PONG
tcp-check comment role\ check
tcp-check send info\ replication\r\n
tcp-check expect string role:master
tcp-check comment QUIT\ phase
tcp-check send QUIT\r\n
tcp-check expect string +OK

forge a HTTP request, then analyze the response
(send many headers before analyzing)
option tcp-check
tcp-check comment forge\ and\ send\ HTTP\ request
tcp-check send HEAD\ /\ HTTP/1.1\r\n
tcp-check send Host:\ www.mydomain.com\r\n
tcp-check send User-Agent:\ HAProxy\ tcpcheck\r\n
tcp-check send \r\n
tcp-check expect rstring HTTP/1\..\ (2..|3..) comment check\ HTTP\ response

Enable or disable the saving of one ACK packet during the accept sequence

When an HTTP connection request comes in, the system acknowledges it on
behalf of HAProxy, then the client immediately sends its request, and the
system acknowledges it too while it is notifying HAProxy about the new
connection. HAProxy then reads the request and responds. This means that we
have one TCP ACK sent by the system for nothing, because the request could
very well be acknowledged by HAProxy when it sends its response.

For this reason, in HTTP mode, HAProxy automatically asks the system to avoid
sending this useless ACK on platforms which support it (currently at least
Linux). It must not cause any problem, because the system will send it anyway
after 40 ms if the response takes more time than expected to come.

During complex network debugging sessions, it may be desirable to disable
this optimization because delayed ACKs can make troubleshooting more complex
when trying to identify where packets are delayed. It is then possible to
fall back to normal behavior by specifying "no option tcp-smart-accept".

It is also possible to force it for non-HTTP proxies by simply specifying
"option tcp-smart-accept". For instance, it can make sense with some services
such as SMTP where the server speaks first.

It is recommended to avoid forcing this option in a defaults section. In case
of doubt, consider setting it back to automatic values by prepending the
"default" keyword before it, or disabling it using the "no" keyword.

Enable or disable the saving of one ACK packet during the connect sequence

On certain systems (at least Linux), HAProxy can ask the kernel not to
immediately send an empty ACK upon a connection request, but to directly
send the buffer request instead. This saves one packet on the network and
thus boosts performance. It can also be useful for some servers, because they
immediately get the request along with the incoming connection.

This feature is enabled when "option tcp-smart-connect" is set in a backend.
It is not enabled by default because it makes network troubleshooting more
complex.

It only makes sense to enable it with protocols where the client speaks first
such as HTTP. In other situations, if there is no data to send in place of
the ACK, a normal ACK is sent.

If this option has been enabled in a "defaults" section, it can be disabled
in a specific instance by prepending the "no" keyword before it.

Enable or disable the sending of TCP keepalive packets on both sides

When there is a firewall or any session-aware component between a client and
a server, and when the protocol involves very long sessions with long idle
periods (e.g. remote desktops), there is a risk that one of the intermediate
components decides to expire a session which has remained idle for too long.

Enabling socket-level TCP keep-alives makes the system regularly send packets
to the other end of the connection, leaving it active. The delay between
keep-alive probes is controlled by the system only and depends both on the
operating system and its tuning parameters.

It is important to understand that keep-alive packets are neither emitted nor
received at the application level. It is only the network stacks which sees
them. For this reason, even if one side of the proxy already uses keep-alives
to maintain its connection alive, those keep-alive packets will not be
forwarded to the other side of the proxy.

Please note that this has nothing to do with HTTP keep-alive.

Using option "tcpka" enables the emission of TCP keep-alive probes on both
the client and server sides of a connection. Note that this is meaningful
only in "defaults" or "listen" sections. If this option is used in a
frontend, only the client side will get keep-alives, and if this option is
used in a backend, only the server side will get keep-alives. For this
reason, it is strongly recommended to explicitly use "option clitcpka" and
"option srvtcpka" when the configuration is split between frontends and
backends.

Enable advanced logging of TCP connections with session state and timers

By default, the log output format is very poor, as it only contains the
source and destination addresses, and the instance name. By specifying
"option tcplog", each log line turns into a much richer format including, but
not limited to, the connection timers, the session status, the connections
numbers, the frontend, backend and server name, and of course the source
address and ports. This option is useful for pure TCP proxies in order to
find which of the client or server disconnects or times out. For normal HTTP
proxies, it's better to use "option httplog" which is even more complete.

"option tcplog" overrides any previous "log-format" directive.

Enable client-side transparent proxying

This option was introduced in order to provide layer 7 persistence to layer 3
load balancers. The idea is to use the OS's ability to redirect an incoming
connection for a remote address to a local process (here HAProxy), and let
this process know what address was initially requested. When this option is
used, sessions without cookies will be forwarded to the original destination
IP address of the incoming request (which should match that of another
equipment), while requests with cookies will still be forwarded to the
appropriate server.

Note that contrary to a common belief, this option does NOT make HAProxy
present the client's IP to the server when establishing the connection.

Executable to run when performing an external-check

<command> is the external command to run

The arguments passed to the to the command are:

<proxy_address> <proxy_port> <server_address> <server_port>

The <proxy_address> and <proxy_port> are derived from the first listener
that is either IPv4, IPv6 or a UNIX socket. In the case of a UNIX socket
listener the proxy_address will be the path of the socket and the
<proxy_port> will be the string "NOT_USED". In a backend section, it's not
possible to determine a listener, and both <proxy_address> and <proxy_port>
will have the string value "NOT_USED".

Some values are also provided through environment variables.

Environment variables :
  HAPROXY_PROXY_ADDR      The first bind address if available (or empty if not
                          applicable, for example in a "backend" section).

  HAPROXY_PROXY_ID        The backend id.

  HAPROXY_PROXY_NAME      The backend name.

  HAPROXY_PROXY_PORT      The first bind port if available (or empty if not
                          applicable, for example in a "backend" section or
                          for a UNIX socket).

  HAPROXY_SERVER_ADDR     The server address.

  HAPROXY_SERVER_CURCONN  The current number of connections on the server.

  HAPROXY_SERVER_ID       The server id.

  HAPROXY_SERVER_MAXCONN  The server max connections.

  HAPROXY_SERVER_NAME     The server name.

  HAPROXY_SERVER_PORT     The server port if available (or empty for a UNIX
                          socket).

  PATH                    The PATH environment variable used when executing
                          the command may be set using "external-check path".

If the command executed and exits with a zero status then the check is
considered to have passed, otherwise the check is considered to have
failed.

external-check command /bin/true

The value of the PATH environment variable used when running an external-check

<path> is the path used when executing external command to run

The default path is "".

external-check path "/usr/bin:/bin"

Enable RDP cookie-based persistence

<name>    is the optional name of the RDP cookie to check. If omitted, the
          default cookie name "msts" will be used. There currently is no
          valid reason to change this name.

This statement enables persistence based on an RDP cookie. The RDP cookie
contains all information required to find the server in the list of known
servers. So when this option is set in the backend, the request is analyzed
and if an RDP cookie is found, it is decoded. If it matches a known server
which is still UP (or if "option persist" is set), then the connection is
forwarded to this server.

Note that this only makes sense in a TCP backend, but for this to work, the
frontend must have waited long enough to ensure that an RDP cookie is present
in the request buffer. This is the same requirement as with the "rdp-cookie"
load-balancing method. Thus it is highly recommended to put all statements in
a single "listen" section.

Also, it is important to understand that the terminal server will emit this
RDP cookie only if it is configured for "token redirection mode", which means
that the "IP address redirection" option is disabled.

listen tse-farm
    bind :3389
    # wait up to 5s for an RDP cookie in the request
    tcp-request inspect-delay 5s
    tcp-request content accept if RDP_COOKIE
    # apply RDP cookie persistence
    persist rdp-cookie
    # if server is unknown, let's balance on the same cookie.
    # alternatively, "balance leastconn" may be useful too.
    balance rdp-cookie
    server srv1 1.1.1.1:3389
    server srv2 1.1.1.2:3389

Set a limit on the number of new sessions accepted per second on a frontend

<rate>    The <rate> parameter is an integer designating the maximum number
          of new sessions per second to accept on the frontend.

When the frontend reaches the specified number of new sessions per second, it
stops accepting new connections until the rate drops below the limit again.
During this time, the pending sessions will be kept in the socket's backlog
(in system buffers) and haproxy will not even be aware that sessions are
pending. When applying very low limit on a highly loaded service, it may make
sense to increase the socket's backlog using the "backlog" keyword.

This feature is particularly efficient at blocking connection-based attacks
or service abuse on fragile servers. Since the session rate is measured every
millisecond, it is extremely accurate. Also, the limit applies immediately,
no delay is needed at all to detect the threshold.

Limit the connection rate on SMTP to 10 per second max
listen smtp
    mode tcp
    bind :25
    rate-limit sessions 10
    server smtp1 127.0.0.1:1025

Note : when the maximum rate is reached, the frontend's status is not changed
       but its sockets appear as "WAITING" in the statistics if the
       "socket-stats" option is enabled.

Return an HTTP redirection if/unless a condition is matched

If/unless the condition is matched, the HTTP request will lead to a redirect
response. If no condition is specified, the redirect applies unconditionally.

<loc>     With "redirect location", the exact value in <loc> is placed into
          the HTTP "Location" header. When used in an "http-request" rule,
          <loc> value follows the log-format rules and can include some
          dynamic values (see Custom Log Format in section 8.2.4).

<pfx>     With "redirect prefix", the "Location" header is built from the
          concatenation of <pfx> and the complete URI path, including the
          query string, unless the "drop-query" option is specified (see
          below). As a special case, if <pfx> equals exactly "/", then
          nothing is inserted before the original URI. It allows one to
          redirect to the same URL (for instance, to insert a cookie). When
          used in an "http-request" rule, <pfx> value follows the log-format
          rules and can include some dynamic values (see Custom Log Format
          in section 8.2.4).

<sch>     With "redirect scheme", then the "Location" header is built by
          concatenating <sch> with "://" then the first occurrence of the
          "Host" header, and then the URI path, including the query string
          unless the "drop-query" option is specified (see below). If no
          path is found or if the path is "*", then "/" is used instead. If
          no "Host" header is found, then an empty host component will be
          returned, which most recent browsers interpret as redirecting to
          the same host. This directive is mostly used to redirect HTTP to
          HTTPS. When used in an "http-request" rule, <sch> value follows
          the log-format rules and can include some dynamic values (see
          Custom Log Format in section 8.2.4).

<code>    The code is optional. It indicates which type of HTTP redirection
          is desired. Only codes 301, 302, 303, 307 and 308 are supported,
          with 302 used by default if no code is specified. 301 means
          "Moved permanently", and a browser may cache the Location. 302
          means "Moved temporarily" and means that the browser should not
          cache the redirection. 303 is equivalent to 302 except that the
          browser will fetch the location with a GET method. 307 is just
          like 302 but makes it clear that the same method must be reused.
          Likewise, 308 replaces 301 if the same method must be used.

<option>  There are several options which can be specified to adjust the
          expected behavior of a redirection :

  - "drop-query"
    When this keyword is used in a prefix-based redirection, then the
    location will be set without any possible query-string, which is useful
    for directing users to a non-secure page for instance. It has no effect
    with a location-type redirect.

  - "append-slash"
    This keyword may be used in conjunction with "drop-query" to redirect
    users who use a URL not ending with a '/' to the same one with the '/'.
    It can be useful to ensure that search engines will only see one URL.
    For this, a return code 301 is preferred.

  - "set-cookie NAME[=value]"
    A "Set-Cookie" header will be added with NAME (and optionally "=value")
    to the response. This is sometimes used to indicate that a user has
    been seen, for instance to protect against some types of DoS. No other
    cookie option is added, so the cookie will be a session cookie. Note
    that for a browser, a sole cookie name without an equal sign is
    different from a cookie with an equal sign.

  - "clear-cookie NAME[=]"
    A "Set-Cookie" header will be added with NAME (and optionally "="), but
    with the "Max-Age" attribute set to zero. This will tell the browser to
    delete this cookie. It is useful for instance on logout pages. It is
    important to note that clearing the cookie "NAME" will not remove a
    cookie set with "NAME=value". You have to clear the cookie "NAME=" for
    that, because the browser makes the difference.

Move the login URL only to HTTPS.
acl clear      dst_port  80
acl secure     dst_port  8080
acl login_page url_beg   /login
acl logout     url_beg   /logout
acl uid_given  url_reg   /login?userid=[^&]+
acl cookie_set hdr_sub(cookie) SEEN=1

redirect prefix   https://mysite.com set-cookie SEEN=1 if !cookie_set
redirect prefix   https://mysite.com           if login_page !secure
redirect prefix   http://mysite.com drop-query if login_page !uid_given
redirect location http://mysite.com/           if !login_page secure
redirect location / clear-cookie USERID=       if logout

Send redirects for request for articles without a '/'.
acl missing_slash path_reg ^/article/[^/]*$
redirect code 301 prefix / drop-query append-slash if missing_slash

Redirect all HTTP traffic to HTTPS when SSL is handled by haproxy.
redirect scheme https if !{ ssl_fc }

Append 'www.' prefix in front of all hosts not having it
http-request redirect code 301 location      \
  http://www.%[hdr(host)]%[capture.req.uri]  \
  unless { hdr_beg(host) -i www }

See section 7 about ACL usage.

Enable or disable session redistribution in case of connection failure

In HTTP mode, if a server designated by a cookie is down, clients may
definitely stick to it because they cannot flush the cookie, so they will not
be able to access the service anymore.

Specifying "redispatch" will allow the proxy to break their persistence and
redistribute them to a working server.

It also allows to retry last connection to another server in case of multiple
connection failures. Of course, it requires having "retries" set to a nonzero
value.

This form is deprecated, do not use it in any new configuration, use the new
"option redispatch" instead.

Add a header at the end of the HTTP request

<string>  is the complete line to be added. Any space or known delimiter
          must be escaped using a backslash ('\'). Please refer to section
          6 about HTTP header manipulation for more information.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

A new line consisting in <string> followed by a line feed will be added after
the last header of an HTTP request.

Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses.

Add "X-Proto: SSL" to requests coming via port 81
acl is-ssl  dst_port       81
reqadd      X-Proto:\ SSL  if is-ssl

Definitely allow an HTTP request if a line matches a regular expression

<search>  is the regular expression applied to HTTP headers and to the
          request line. This is an extended regular expression. Parenthesis
          grouping is supported and no preliminary backslash is required.
          Any space or known delimiter must be escaped using a backslash
          ('\'). The pattern applies to a full line at a time. The
          "reqallow" keyword strictly matches case while "reqiallow"
          ignores case.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

A request containing any line which matches extended regular expression
<search> will mark the request as allowed, even if any later test would
result in a deny. The test applies both to the request line and to request
headers. Keep in mind that URLs in request line are case-sensitive while
header names are not.

It is easier, faster and more powerful to use ACLs to write access policies.
Reqdeny, reqallow and reqpass should be avoided in new designs.

# allow www.* but refuse *.local
reqiallow ^Host:\ www\.
reqideny  ^Host:\ .*\.local

Delete all headers matching a regular expression in an HTTP request

<search>  is the regular expression applied to HTTP headers and to the
          request line. This is an extended regular expression. Parenthesis
          grouping is supported and no preliminary backslash is required.
          Any space or known delimiter must be escaped using a backslash
          ('\'). The pattern applies to a full line at a time. The "reqdel"
          keyword strictly matches case while "reqidel" ignores case.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

Any header line matching extended regular expression <search> in the request
will be completely deleted. Most common use of this is to remove unwanted
and/or dangerous headers or cookies from a request before passing it to the
next servers.

Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses. Keep in mind that header names are not case-sensitive.

# remove X-Forwarded-For header and SERVER cookie
reqidel ^X-Forwarded-For:.*
reqidel ^Cookie:.*SERVER=

Deny an HTTP request if a line matches a regular expression

<search>  is the regular expression applied to HTTP headers and to the
          request line. This is an extended regular expression. Parenthesis
          grouping is supported and no preliminary backslash is required.
          Any space or known delimiter must be escaped using a backslash
          ('\'). The pattern applies to a full line at a time. The
          "reqdeny" keyword strictly matches case while "reqideny" ignores
          case.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

A request containing any line which matches extended regular expression
<search> will mark the request as denied, even if any later test would
result in an allow. The test applies both to the request line and to request
headers. Keep in mind that URLs in request line are case-sensitive while
header names are not.

A denied request will generate an "HTTP 403 forbidden" response once the
complete request has been parsed. This is consistent with what is practiced
using ACLs.

It is easier, faster and more powerful to use ACLs to write access policies.
Reqdeny, reqallow and reqpass should be avoided in new designs.

# refuse *.local, then allow www.*
reqideny  ^Host:\ .*\.local
reqiallow ^Host:\ www\.

Ignore any HTTP request line matching a regular expression in next rules

<search>  is the regular expression applied to HTTP headers and to the
          request line. This is an extended regular expression. Parenthesis
          grouping is supported and no preliminary backslash is required.
          Any space or known delimiter must be escaped using a backslash
          ('\'). The pattern applies to a full line at a time. The
          "reqpass" keyword strictly matches case while "reqipass" ignores
          case.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

A request containing any line which matches extended regular expression
<search> will skip next rules, without assigning any deny or allow verdict.
The test applies both to the request line and to request headers. Keep in
mind that URLs in request line are case-sensitive while header names are not.

It is easier, faster and more powerful to use ACLs to write access policies.
Reqdeny, reqallow and reqpass should be avoided in new designs.

# refuse *.local, then allow www.*, but ignore "www.private.local"
reqipass  ^Host:\ www.private\.local
reqideny  ^Host:\ .*\.local
reqiallow ^Host:\ www\.

Replace a regular expression with a string in an HTTP request line

<search>  is the regular expression applied to HTTP headers and to the
          request line. This is an extended regular expression. Parenthesis
          grouping is supported and no preliminary backslash is required.
          Any space or known delimiter must be escaped using a backslash
          ('\'). The pattern applies to a full line at a time. The "reqrep"
          keyword strictly matches case while "reqirep" ignores case.

<string>  is the complete line to be added. Any space or known delimiter
          must be escaped using a backslash ('\'). References to matched
          pattern groups are possible using the common \N form, with N
          being a single digit between 0 and 9. Please refer to section
          6 about HTTP header manipulation for more information.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

Any line matching extended regular expression <search> in the request (both
the request line and header lines) will be completely replaced with <string>.
Most common use of this is to rewrite URLs or domain names in "Host" headers.

Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses. Note that for increased readability, it is suggested to add enough
spaces between the request and the response. Keep in mind that URLs in
request line are case-sensitive while header names are not.

# replace "/static/" with "/" at the beginning of any request path.
reqrep ^([^\ :]*)\ /static/(.*)     \1\ /\2
# replace "www.mydomain.com" with "www" in the host name.
reqirep ^Host:\ www.mydomain.com   Host:\ www

Tarpit an HTTP request containing a line matching a regular expression

<search>  is the regular expression applied to HTTP headers and to the
          request line. This is an extended regular expression. Parenthesis
          grouping is supported and no preliminary backslash is required.
          Any space or known delimiter must be escaped using a backslash
          ('\'). The pattern applies to a full line at a time. The
          "reqtarpit" keyword strictly matches case while "reqitarpit"
          ignores case.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

A request containing any line which matches extended regular expression
<search> will be tarpitted, which means that it will connect to nowhere, will
be kept open for a pre-defined time, then will return an HTTP error 500 so
that the attacker does not suspect it has been tarpitted. The status 500 will
be reported in the logs, but the completion flags will indicate "PT". The
delay is defined by "timeout tarpit", or "timeout connect" if the former is
not set.

The goal of the tarpit is to slow down robots attacking servers with
identifiable requests. Many robots limit their outgoing number of connections
and stay connected waiting for a reply which can take several minutes to
come. Depending on the environment and attack, it may be particularly
efficient at reducing the load on the network and firewalls.

# ignore user-agents reporting any flavor of "Mozilla" or "MSIE", but
# block all others.
reqipass   ^User-Agent:\.*(Mozilla|MSIE)
reqitarpit ^User-Agent:

# block bad guys
acl badguys src 10.1.0.3 172.16.13.20/28
reqitarpit . if badguys

Set the number of retries to perform on a server after a connection failure

<value>   is the number of times a connection attempt should be retried on
          a server when a connection either is refused or times out. The
          default value is 3.

It is important to understand that this value applies to the number of
connection attempts, not full requests. When a connection has effectively
been established to a server, there will be no more retry.

In order to avoid immediate reconnections to a server which is restarting,
a turn-around timer of min("timeout connect", one second) is applied before
a retry occurs.

When "option redispatch" is set, the last retry may be performed on another
server even if a cookie references a different server.

Add a header at the end of the HTTP response

<string>  is the complete line to be added. Any space or known delimiter
          must be escaped using a backslash ('\'). Please refer to section
          6 about HTTP header manipulation for more information.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

A new line consisting in <string> followed by a line feed will be added after
the last header of an HTTP response.

Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses.

Delete all headers matching a regular expression in an HTTP response

<search>  is the regular expression applied to HTTP headers and to the
          response line. This is an extended regular expression, so
          parenthesis grouping is supported and no preliminary backslash
          is required. Any space or known delimiter must be escaped using
          a backslash ('\'). The pattern applies to a full line at a time.
          The "rspdel" keyword strictly matches case while "rspidel"
          ignores case.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

Any header line matching extended regular expression <search> in the response
will be completely deleted. Most common use of this is to remove unwanted
and/or sensitive headers or cookies from a response before passing it to the
client.

Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses. Keep in mind that header names are not case-sensitive.

# remove the Server header from responses
rspidel ^Server:.*

Block an HTTP response if a line matches a regular expression

<search>  is the regular expression applied to HTTP headers and to the
          response line. This is an extended regular expression, so
          parenthesis grouping is supported and no preliminary backslash
          is required. Any space or known delimiter must be escaped using
          a backslash ('\'). The pattern applies to a full line at a time.
          The "rspdeny" keyword strictly matches case while "rspideny"
          ignores case.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

A response containing any line which matches extended regular expression
<search> will mark the request as denied. The test applies both to the
response line and to response headers. Keep in mind that header names are not
case-sensitive.

Main use of this keyword is to prevent sensitive information leak and to
block the response before it reaches the client. If a response is denied, it
will be replaced with an HTTP 502 error so that the client never retrieves
any sensitive data.

It is easier, faster and more powerful to use ACLs to write access policies.
Rspdeny should be avoided in new designs.

# Ensure that no content type matching ms-word will leak
rspideny  ^Content-type:\.*/ms-word

Replace a regular expression with a string in an HTTP response line

<search>  is the regular expression applied to HTTP headers and to the
          response line. This is an extended regular expression, so
          parenthesis grouping is supported and no preliminary backslash
          is required. Any space or known delimiter must be escaped using
          a backslash ('\'). The pattern applies to a full line at a time.
          The "rsprep" keyword strictly matches case while "rspirep"
          ignores case.

<string>  is the complete line to be added. Any space or known delimiter
          must be escaped using a backslash ('\'). References to matched
          pattern groups are possible using the common \N form, with N
          being a single digit between 0 and 9. Please refer to section
          6 about HTTP header manipulation for more information.

<cond>    is an optional matching condition built from ACLs. It makes it
          possible to ignore this rule when other conditions are not met.

Any line matching extended regular expression <search> in the response (both
the response line and header lines) will be completely replaced with
<string>. Most common use of this is to rewrite Location headers.

Header transformations only apply to traffic which passes through HAProxy,
and not to traffic generated by HAProxy, such as health-checks or error
responses. Note that for increased readability, it is suggested to add enough
spaces between the request and the response. Keep in mind that header names
are not case-sensitive.

# replace "Location: 127.0.0.1:8080" with "Location: www.mydomain.com"
rspirep ^Location:\ 127.0.0.1:8080    Location:\ www.mydomain.com

Declare a server in a backend

<name>    is the internal name assigned to this server. This name will
          appear in logs and alerts. If "http-send-name-header" is
          set, it will be added to the request header sent to the server.

<address> is the IPv4 or IPv6 address of the server. Alternatively, a
          resolvable hostname is supported, but this name will be resolved
          during start-up. Address "0.0.0.0" or "*" has a special meaning.
          It indicates that the connection will be forwarded to the same IP
          address as the one from the client connection. This is useful in
          transparent proxy architectures where the client's connection is
          intercepted and haproxy must forward to the original destination
          address. This is more or less what the "transparent" keyword does
          except that with a server it's possible to limit concurrency and
          to report statistics. Optionally, an address family prefix may be
          used before the address to force the family regardless of the
          address format, which can be useful to specify a path to a unix
          socket with no slash ('/'). Currently supported prefixes are :
                - 'ipv4@'  -> address is always IPv4
                - 'ipv6@'  -> address is always IPv6
                - 'unix@'  -> address is a path to a local unix socket
                - 'abns@'  -> address is in abstract namespace (Linux only)
                - 'sockpair@' -> address is the FD of a connected unix
                  socket or of a socketpair. During a connection, the
                  backend creates a pair of connected sockets, and passes
                  one of them over the FD. The bind part will use the
                  received socket as the client FD. Should be used
                  carefully.
          You may want to reference some environment variables in the
          address parameter, see section 2.3 about environment
          variables. The "init-addr" setting can be used to modify the way
          IP addresses should be resolved upon startup.

<port>    is an optional port specification. If set, all connections will
          be sent to this port. If unset, the same port the client
          connected to will be used. The port may also be prefixed by a "+"
          or a "-". In this case, the server's port will be determined by
          adding this value to the client's port.

<param*>  is a list of parameters for this server. The "server" keywords
          accepts an important number of options and has a complete section
          dedicated to it. Please refer to section 5 for more details.

server first  10.1.1.1:1080 cookie first  check inter 1000
server second 10.1.1.2:1080 cookie second check inter 1000
server transp ipv4@
server backup "${SRV_BACKUP}:1080" backup
server www1_dc1 "${LAN_DC1}.101:80"
server www1_dc2 "${LAN_DC2}.101:80"

Note: regarding Linux's abstract namespace sockets, HAProxy uses the whole
      sun_path length is used for the address length. Some other programs
      such as socat use the string length only by default. Pass the option
      ",unix-tightsocklen=0" to any abstract socket definition in socat to
      make it compatible with HAProxy's.

Set the server state file to read, load and apply to servers available in
this backend. It only applies when the directive "load-server-state-from-file"
is set to "local". When <file> is not provided or if this directive is not
set, then backend name is used. If <file> starts with a slash '/', then it is
considered as an absolute path. Otherwise, <file> is concatenated to the
global directive "server-state-file-base".

The minimal configuration below would make HAProxy look for the state server file '/etc/haproxy/states/bk':
global
  server-state-file-base /etc/haproxy/states

backend bk
  load-server-state-from-file

Set a template to initialize servers with shared parameters.
The names of these servers are built from <prefix> and <num | range> parameters.

<prefix>  A prefix for the server names to be built.

<num | range>
          If <num> is provided, this template initializes <num> servers
          with 1 up to <num> as server name suffixes. A range of numbers
          <num_low>-<num_high> may also be used to use <num_low> up to
          <num_high> as server name suffixes.

<fqdn>    A FQDN for all the servers this template initializes.

<port>    Same meaning as "server" <port> argument (see "server" keyword).

<params*>
          Remaining server parameters among all those supported by "server"
          keyword.

# Initializes 3 servers with srv1, srv2 and srv3 as names,
# google.com as FQDN, and health-check enabled.
server-template srv 1-3 google.com:80 check

# or
server-template srv 3 google.com:80 check

# would be equivalent to:
server srv1 google.com:80 check
server srv2 google.com:80 check
server srv3 google.com:80 check

Set the source address for outgoing connections