Getting Started With Molecule

The following guide will step through an example of developing and testing a new Ansible collection. After reading this guide, you should be familiar with the basics of how to use Molecule and what it can offer.

1. Create a collection

   One of the recommended ways to create a collection is to place it under a collections/ansible_collections directory. If you don't put your collection into a directory named ansible_collections, molecule won't be able to find your role.

     ansible-galaxy collection init foo.bar
   

2. cd to the roles directory in your new collection.

3. Initialize a new role for this collection.

     ansible-galaxy role init my_role
   

4. Add a task under my_role/tasks/main.yml.

   ---
   - name: Task is running from within the role
     ansible.builtin.debug:
       msg: "This is a task from my_role."
   

5. At the root of your new collection, create a directory named playbooks.

6. cd to the playbooks directory and create a new playbook called my_playbook.yml

   ---
   - name: Test new role from within this playbook
     hosts: localhost
     gather_facts: false
     tasks:
       - name: Testing role
         ansible.builtin.include_role:
           name: foo.bar.my_role
           tasks_from: main.yml
   

7. Adding Molecule to the Collection

   1. Create a new directory in your collection called extensions.

   2. cd to the extensions directory and initialize a new default molecule scenario.

         molecule init scenario
      

Before moving to test the playbooks or roles, the sections below provide information related to Scenarios.

Molecule Scenarios

Scenarios are the starting point for a lot of powerful functionality that Molecule offers. For now, we can think of a scenario as a test suite for roles or playbooks within a collection. You can have as many scenarios as you like and Molecule will run one after the other.

The Scenario Layout

Within the molecule/default folder, we find several files and directories:

$ ls
create.yml  destroy.yml  molecule.yml  converge.yml

• create.yml is a playbook file used for creating the instances and storing data in instance-config
• destroy.yml has the Ansible code for destroying the instances and removing them from instance-config
• molecule.yml is the central configuration entry point for Molecule per scenario. With this file, you can configure each tool that Molecule will employ when testing your role.
• converge.yml is the playbook file that contains the call for your role. Molecule will invoke this playbook with ansible-playbook and run it against an instance created by the driver.

Note

If the verify.yml playbook does not explicitly include_role your role, the library and module_utils provided by your role are not available in the playbook by default. If you need those for testing but would like to avoid re-running your role, consider adding an empty task file init.yml to your role and use tasks_from to include your role in the verify.yml playbook:

- name: Verify
  hosts: all
  become: true
  tasks:
    - name: Initialize role without actually running it
      ansible.builtin.include_role:
        name: my_role
        tasks_from: init

# Start testing: can use role library now

Inspecting the molecule.yml

The molecule.yml is for configuring Molecule. It is a YAML file whose keys represent the high-level components that Molecule provides. These are:

• The dependency manager. Molecule uses galaxy development guide by default to resolve your role dependencies.
• The driver provider. Molecule uses the Delegated driver by default. Molecule uses the driver to delegate the task of creating instances.
• The platforms definitions. Molecule relies on this to know which instances to create, name and to which group each instance belongs. If you need to test your role against multiple popular distributions (CentOS, Fedora, Debian), you can specify that in this section.
• The provisioner. Molecule only provides an Ansible provisioner. Ansible manages the life cycle of the instance based on this configuration.
• The scenario definition. Molecule relies on this configuration to control the scenario sequence order.
• The verifier framework. Molecule uses Ansible by default to provide a way to write specific state checking tests (such as deployment smoke tests) on the target instance.

Run a full test sequence

Molecule provides commands for manually managing the lifecycle of the instance, scenario, development and testing tools. However, we can also tell Molecule to manage this automatically within a scenario sequence.

cd to the extensions directory.

The full lifecycle sequence can be invoked with:

molecule test

Molecule full lifecycle sequence
└── default
    ├── dependency
    ├── cleanup
    ├── destroy
    ├── syntax
    ├── create
    ├── prepare
    ├── converge
    ├── idempotence
    ├── side_effect
    ├── verify
    ├── cleanup
    └── destroy

Note

It can be particularly useful to pass the --destroy=never flag when invoking molecule test so that you can tell Molecule to run the full sequence but not destroy the instance if one step fails.

If the --platform-name=[PLATFORM_NAME] flag is passed or the environment variable MOLECULE_PLATFORM_NAME is exposed when invoking molecule test, it can tell Molecule to run the test in one platform only. It is useful if you want to test one platform docker image.

Test the collection playbook or role

So you now have an isolated test environment, and can also use it for live development, by running molecule converge. It will run through the same steps as above but will stop after the converge action. Then you can make changes to your collection or the Converge play, and then run molecule converge again (and again) until you're done with your development work.

One of the default files created as part of the initialization is the converge.yml file. This file is a playbook created to run your role from start to finish. This can be modified if needed but is a good place to start if you have never used Molecule before.

To test the playbook, we update converge.yml:

---
- name: Include a playbook from a collection
  ansible.builtin.import_playbook: foo.bar.my_playbook

Similarly, if we want to test only the role instead of a playbook in converge.yml file:

---
- name: Include a role from a collection
  hosts: localhost
  gather_facts: false
  tasks:
    - name: Testing role
      ansible.builtin.include_role:
        name: foo.bar.my_role
        tasks_from: main.yml

cd to the extensions directory.

molecule converge

The above command runs the same steps as molecule test for the default scenario, but will stop after the converge action.