I started to dive into docker and was going to write a post about that but I got a little off track along the way and found molecule instead. Molecule is a nice tool for testing ansible code using docker or various VM providers. There are a number of blog posts that cover some basic examples of molecule, so I'll try to deviate a bit. Molecule does have a bit of a learning curve, but if you know a little python and ansible then you should be able to figure it out. But the main trouble is the documentation isn't written for someone who is unfamiliar with it. So this post hopes to clear up some of the questions you may have when first starting out.

Basic Usage

Since its probably a safe bet that we already have some ansible roles, we just need to initialize the test scenario. The first scenario needs to be named "default", though I'm not really sure why.

molecule init scenario --scenario-name default --role-name <role_name>

If we are starting a new role from scratch we can simply run and it will create both the empty role folder structure and a default scenario.

molecule init role -r <role_name>

Now, we know this default scenario is not set up for systemd, so how do we make systemd part of the default? I'm not sure, but we'll return to that thought. The next molecule command we need is the actual test command.

molecule test

It doesn't get any easier than that does it. This will at a bare minimum run through the ansible role twice and finally run yamllint. If you have multiple scenarios you can also specify if you want to run all or a specific one with -s <scenario_name>.

Common Issues

Systemd in Docker

The first issue I had and actually what led to me finding molecule was trying to use systemd inside a docker container. Since most classic ansible roles will at some point need to interact with services systemd is a common requirement. Within the molecule scenario you'll have a molecule.yml file which has the docker settings you'll need to change. First, we need to change the image to use one that has systemd. There is an official centos/systemd image available so let's go with that. Note, this won't work well with firewalld but we'll deal with that later.

platforms:
  - name: instance
    image: centos/systemd
    volume_mounts:
        - "/sys/fs/cgroup:/sys/fs/cgroup:rw"
    command: "/usr/sbin/init"
    privileged: True

Angry Linting

If you add a molecule scenario to an existing role it leaves out the default .yamllint file and so you get yelled at about molecule syntax as well as your own. Go ahead and grab the .yamllint from https://github.com/metacloud/molecule/blob/master/.yamllint or by creating a new role with molecule and copy it into the directory of your existing role.

Conclusion

Hopefully, this gave you enough information to get started with molecule and up your ansible game. Next up will be adding tests to ensure your ansible role is doing what you want it to and multi-node/multi-role testing.