Null Resource

The null_resource resource implements the standard resource lifecycle but takes no further action.

The triggers argument allows specifying an arbitrary set of values that, when changed, will cause the resource to be replaced.

Example Usage

The primary use-case for the null resource is as a do-nothing container for arbitrary actions taken by a provisioner, as follows:

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

In this example, three EC2 instances are created and then a null_resource instance is used to gather data about all three and execute a single action that affects them all. Due to the triggers map, the null_resource will be replaced each time the instance ids change, and thus the remote-exec provisioner will be re-run.

Argument Reference

The following arguments are supported:

• triggers - (Optional) A map of arbitrary strings that, when changed, will force the null resource to be replaced, re-running any associated provisioners.

Attributes Reference

The following attributes are exported:

• id - An arbitrary value that changes each time the resource is replaced. Can be used to cause other resources to be updated or replaced in response to null_resource changes.