Tests for the Arch Linux infrastructure

The Arch Linux DevOps team uses a combination of Ansible and Terraform to manage their hosts. If you want to have a look on their infrastructure repository, you can do so via this link: https://git.archlinux.org/infrastructure.git/tree/

The combination of Ansible and Terraform works quite well for Arch Linux, the only subject we are missing is proper testing. I want to present a small proof of concept on how we could do tests in the future. My approach uses molecule for testing. Molecule utilizes Vagrant and Docker for running the Ansible Playbooks.

Arch Linux provides images for both of them, since quite a while now. These projects are called Arch-Boxes and Archlinux-Docker. Therefore it makes sense to reuse them infrastructure tests.

The actual tests are written in Python with support of the library testinfra.

First of all we need to install the dependencies. You can find most of our needed tools in our repositories:

  • ansible
  • python-pip
  • python
  • flake8
  • ansible-lint
  • docker
  • vagrant

What we are missing right now is molecule. We can install molecule with the vagrant dependencies via pip install molecule[vagrant] --user. Pip will install all needed packages to our $HOME.

So let us pick a first role we want to test:

infrastructure/roles/sshd:

❯ ls -la
drwxr-xr-x - chris 15 Dec  2019 handlers
drwxr-xr-x - chris 15 Dec  2019 tasks
drwxr-xr-x - chris 15 Dec  2019 templates

We can initialize a molecule test scenario on an already existing Ansible role via molecule init scenario --role-name sshd --driver-name vagrant. The command is going to create a molecule directory for us. The created directory will have this structure:

❯ tree molecule 
molecule
└── default
   ├── INSTALL.rst
   ├── molecule.yml
   ├── playbook.yml
   ├── prepare.yml
   └── tests
      ├── __pycache__
      │  ├── test_default.cpython-38-pytest-5.3.5.pyc
      │  └── test_default.cpython-38.pyc
      └── test_default.py

The interesting files we will have a look at are molecule.yml, prepare.yml and test_default.py. In molecule.yml we configure basic molecule behavior. In prepare.yml we can do first preparations with Ansible (we need to do this, because Arch Linux is slightly different to distributions the molecule team normally uses). test_default.py stores our tests as testinfra functions.

The molecule.yml shouldn’t be so different for Arch Linux to the one that is usually generated by molecule, but let me highlight the changes:

infrastructure/roles/sshd/molecule/default/molecule.yml:

---
dependency:
  name: galaxy
driver:
  # We use Vagrant here, because we have other roles that need kernel modules etc
  name: vagrant
  provider:
    name: virtualbox
lint:
  name: yamllint
platforms:
  # Here we specify our official archlinux/archlinux image
  - name: instance
    box: archlinux/archlinux
provisioner:
  name: ansible
  lint:
    name: ansible-lint
  # This option is important. The Ansible infrastructure roles use root on default.
  # So we need to gain privilege via sudo and become root for running all roles.
  connection_options:
    ansible_become: true
verifier:
  name: testinfra
  lint:
    name: flake8

prepare.yml includes some magic, regarding mirror setup, installing python and a fresh restart. We need this mirror setup tasks, because we are just enabling all mirrors in our Arch Linux Vagrant box right now. This leads to slow mirrors. I am going to fix this in a new Arch-Boxes release. For now I just set static mirrors from which I know that they are fast for my location. In the second prepare.yml task we need to install python for Ansible. Consider that I use pacman -Syu here, because I want a full system upgrade, everything else will lead us into trouble when playing around with kernel modules (Arch Linux provides still no nice way to use kernel modules when you’ve installed a new kernel). Due to the full system upgrade, we need to reboot for making sure that we boot into the new kernel.

infrastructure/roles/sshd/molecule/default/prepare.yml

---
- name: Prepare
  hosts: all
  gather_facts: false
  tasks:
    - name: Setup fast mirror
      raw: echo -e "Server = https://mirror.metalgamer.eu/archlinux/\$repo/os/\$arch\nServer = https://mirror.metalgamer.eu/archlinux/\$repo/os/\$arch\nhttps://ftp.spline.inf.fu-berlin.de/mirrors/archlinux/\$repo/os/\$arch" > /etc/pacman.d/mirrorlist
      become: true
    - name: Install python for Ansible
      raw: test -e /usr/bin/python || (pacman -Syu --noconfirm python)
      become: true
      changed_when: false
    - name: Reboot for kernel updates
      reboot:

The last important file is test_default.py. test_default.py stores our unit tests for the Ansible roles. Right now I am just checking for an installed openssh package and a running and enabled sshd daemon. The usage of testinfra should be self-explanatory, however I didn’t make experience with more complex tasks like comparing templates yet. I can imagine that this will become very tedious for us. The future will show if the usage of testinfra suits our demands. If not we either use a different library or we need to stay with Ansible and YAML linting + tests on clean VMs or Docker containers. Both of them would be already far better than the current situation with no tests at all.

infrastructure/roles/sshd/molecule/default/tests/test_default.py:

import os

import testinfra.utils.ansible_runner

testinfra_hosts = testinfra.utils.ansible_runner.AnsibleRunner(
    os.environ['MOLECULE_INVENTORY_FILE']
).get_hosts('all')


def test_openssh_is_installed(host):
    openssh = host.package("openssh")
    assert openssh.is_installed


def test_openssh_is_running_and_enabled(host):
    openssh = host.service("sshd")
    assert openssh.is_running
    assert openssh.is_enabled

For running our tests we can trigger molecule test from inside of our sshd role directory. I haven’t played around with molecule converge yet, but I guess this is the command you would use for local Ansible development. molecule test will trigger a clean environment on every test (destroying the VM snapshot etc). This is pretty cost intensive and takes time.

If you are interested in this work, you can follow my branch on github:

https://github.com/shibumi/infrastructure/tree/shibumi/molecule-tests


793 Words

2020-02-05 20:57 +0000