»Provisioners Without a Resource

If you need to run provisioners that aren't directly associated with a specific resource, you can associate them with a null_resource.

Instances of null_resource are treated like normal resources, but they don't do anything. Like with any other resource, you can configure provisioners and connection details on a null_resource. You can also use its triggers argument and any meta-arguments to control exactly where in the dependency graph its provisioners will run.

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 cluster
    inline = [
      "bootstrap-cluster.sh ${join(" ", aws_instance.cluster.*.private_ip)}",
    ]
  }
}

Argument Reference

In addition to meta-arguments supported by all resources, null_resource supports the following specific arguments:

• triggers - A map of values which should cause this set of provisioners to re-run. Values are meant to be interpolated references to variables or attributes of other resources.