Ansible inventory generated from Terraform.

When creating an infrastructure with Terraform, it is nice to have Terraform create the Ansible inventory file for us. To achive this it is possible to utilize the Terraform templates for generation of hostnames and the actual inventory file. All code can be found here

The Templates

First we create the template for our hostnames following our naming convention:

${name}-${env}-${format("%02s",index)} ${extra}

Next we create the template for our Ansible inventory, where in this case we only have one set of hosts, and we utilize grouping of those hosts under a production group. This allows us to specify environment specific variables via group vars.

[web]
${web_hosts}

[${env}:children]
web

Terraform file

In our terraform file we use two template_file definitions to generate both the hostnames and the ansible inventory. In this example we ‘fake’ the IP’s by defining a list, but in real life this would be a list of ipadresses from a resource (e.g. aws_instance).

variable "web_ips"  { default = "10.0.0.1,10.0.0.2,10.0.0.3" }

resource "template_file" "web_ansible" {
  count = "${length(split(",",var.web_ips))}"
  template = "${file("${path.module}/hostname.tpl")}"
  vars {
    index = "${count.index + 1}"
    name  = "web"
    env   = "p"
    extra = " ansible_host=${element(split(",",var.web_ips),count.index)}"
    # extra = ""
  }
}

resource "template_file" "ansible_inventory" {
  template = "${file("${path.module}/ansible_inventory.tpl")}"
  vars {
    env         = "production"
    web_hosts   = "${join("\n",template_file.web_ansible.*.rendered)}"
  }
}

output "ansible_inventory" {
	value = "${template_file.ansible_hosts.rendered}"
}

Execution and Result

Now applying the terraform file, and calling the ‘output’ command from terraform we can create our inventory:

$ terraform apply 
$ terraform output ansible_inventory > inventory

giving the following result:

$ cat inventory
[web]
web-p-01  ansible_host=10.0.0.1
web-p-02  ansible_host=10.0.0.2
web-p-03  ansible_host=10.0.0.3

[production:children]
web