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Bootstrapping molecule instances with volumes

We use Ansible for all kinds of things. One of it being formatting and mounting a volume to be able to use it.

When I introduced the code for that, it worked (flawlessly, of course) — until I hit a bug when I provisioned another cluster. Long story short, I was able to fix the bug. But since we rely on it to work always, and I wanted to make sure I had all situations covered, I decided to extend one of our tests.


We currently use Hetzer Cloud to bootstrap instances for CI. They are pretty okay. At times, you have odd issues where CPU hangs or a server doesn't respond to SSH. But since it's cheap, it hasn't bothered me enough yet to find something else. Add to that, they are European (slightly less issues with data privacy, etc.), know how VAT work (means, the invoices are correct) and allow for SEPA to pay for invoices (means, less credit card fees, no currency conversions, etc.).

Extending the test

A molecule scenario is driven by a file called molecule.yml. It'll look similar to this:

  name: galaxy
  name: hetznercloud
  name: yamllint
  - name: node-01-${DRONE_BUILD_NUMBER:-111}
    server_type: cx11
    image: centos-7
  - name: node-02-${DRONE_BUILD_NUMBER:-111}
    server_type: cx11
    image: centos-7
  name: ansible
      pipelining: True
    name: ansible-lint
  name: testinfra
    name: flake8

Most of it is as generated, we added different names though as this test requires multiple instances and we wanted to run multiple builds at the same time, which is why we append $DRONE_BUILD_NUMBER from the environment. (The last bit, ensures the number is still set when you drone exec for a build locally.

TL;DR — the scenario will have two instances available: node-01-XYZ and node-02-XYZ.

Going from there, you have two additional files of interest: create.yml and destroy.yml.

The first is used to bootstrap instances through Ansible's hcloud_server module, the second cleans up after the scenario/build finished.

Adding the volume

In create.yml, I added the following task after "Wait for instance(s) creation to complete":

- name: Attach a volume
    name: "my-volume-{{ }}"
    server: "{{ }}"
    size: 15
    automount: no
    state: present
  with_items: "{{ molecule_yml.platforms }}"

The task uses Ansible's hcloud_volume and ensures each of my nodes has a 15 GiB volume attached. The volume is called "my-volume" and gets the name of the instance (e.g. node-01-XYZ suffixed). For our purposes, we also decided to attach it, without mounting it as we take care of that with our Ansible role.

Deleting the volume(s)

To save a few bucks and to clean up after each test run. Open destroy.yml and add the following block after the instances are terminated:

- name: Delete volume(s)
    - name: Detach a volume
        name: "my-volume-{{ item.instance }}"
        state: absent
      with_items: "{{ instance_conf }}"
  ignore_errors: yes
  when: not skip_instances

Side note

Another neat trick is that if you add variables in molecule.yml in platforms, like so.

For example, to set the size of the volume try the following:

  - name: instance
    disk_size: 20

And then use that variable with the hcloud_volume task as {{ item.disk_size }} later. And if disk size is not your objective, you could control here if each instance gets a volume, or if you only need it for certain roles in your setup. This is all a hack and maybe it'll go away, but for the time being I am glad no one bothered to validate these YAML keys or applied a schema.


Thanks for reading!