Terraform meets Ansible: Seamless inventory integration with the new certified collection

You probably know the drill.

Terraform is great for resource provisioning, and Ansible is great for configuration management. A very common workflow is to combine both to automatically provision and configure virtual machines. Terraform is used to provision virtual machines, and Ansible is then used to configure them. However, in order for this to work you need to define Ansible inventory based on Terraform outputs.

If you go around searching for ways to populate Ansible inventory from Terraform, you’d mostly see solutions templating inventory files. Templating and inventory scripts based solutions are outdated at this point. Inventory plugins are the most recent and capable way to manage dynamic inventory in Ansible.

In late 2022 Red Hat announced the cloud.terraform certified collection. Later on in 2023 Red Hat released a Terraform provider for Ansible and a matching inventory plugin for defining inventory as Terraform resources.

I’m migrating from my custom inventory plugins to this new official inventory plugin and Terraform provider duo, and it feels like there’s not enough information about it around.

The instructions

In this guide we’ll define Ansible inventory using Terraform, and configure Ansible to use the inventory resources.

This guide assumes you have Ansible 8.5 or later, and Terraform 1.6 or later installed. It assumes your repository has a terraform directory containing a Terraform module, and a playbook directory containing an Ansible playbook.

Add the ansible/ansible Terraform provider to the provider requirements:

# Inside terraform/versions.tf
terraform {
  required_providers {
    ansible = {
      source  = "ansible/ansible"
      version = "1.3.0"
    }
  }
}

Initialize Terraform to download the provider:

terraform init

Create Ansible inventory group and host resources:

# Inside terraform/main.tf
resource "ansible_group" "cluster" {
  name     = "k8s_cluster"
  children = ["kube_control_plane", "kube_node"]
}

resource "ansible_host" "debug" {
  name   = "rocky-debug"
  groups = ["kube_control_plane", "kube_node", "etcd"]
  variables = {
    ansible_host = libvirt_domain.debug.network_interface[0].addresses[0]
  }
}

Apply the module to create the inventory resources:

terraform apply

Moving over to the playbook directory, add the cloud.terraform collection requirement:

# Inside playbook/requirements.yml
collections:
  - name: cloud.terraform
    version: 3.0.0

Install collection requirements:

ansible-galaxy collection install --requirements requirements.yml

Create an inventory configuration file:

# Inside playbook/inventory/nodes/hosts.yml
plugin: cloud.terraform.terraform_provider
project_path: ../terraform

Verify the Ansible inventory is actually present:

ansible-inventory -i inventory/nodes/hosts.yml --graph

Output should look like this:

@all:
  |--@ungrouped:
  |--@k8s_cluster:
  |  |--@kube_control_plane:
  |  |  |--rocky-debug
  |  |--@kube_node:
  |  |  |--rocky-debug
  |--@etcd:
  |  |--rocky-debug

Run it

Only thing left is to run your playbook.

You now know how to use the latest and greatest Terraform integration Ansible has to offer. How will you be using it?