null_resource

The null_resource is a resource that allows you to configure provisioners that are not directly associated with a single existing resource.

A null_resource behaves exactly like any other resource, so you configure provisioners, connection details, and other meta-parameters in the same way you would on any other resource.

This allows fine-grained control over when provisioners run in the dependency graph.

Example usage

resource "aws_instance" "cluster" {
  count = 3

  # ...
}

resource "null_resource" "cluster" {
  # Changes to any instance of the cluster requires re-provisioning
  triggers {
    cluster_instance_ids = "${join(",", aws_instance.cluster.*.id)}"
  }

  # Bootstrap script can run on any instance of the cluster
  # So we just choose the first in this case
  connection {
    host = "${element(aws_instance.cluster.*.public_ip, 0)}"
  }

  provisioner "remote-exec" {
    # Bootstrap script called with private_ip of each node in the clutser
    inline = [
      "bootstrap-cluster.sh ${join(" ", aws_instance.cluster.*.private_ip)}",
    ]
  }
}

Argument Reference

In addition to all the resource configuration available, null_resource supports the following specific configuration options:

• triggers - A mapping of values which should trigger a rerun of this set of provisioners. Values are meant to be interpolated references to variables or attributes of other resources.