A guide on how to write effective and fault tolerant Ansible code.

Ansible code convention:

• Descriptions are not capitalized

- name: ensuring something

• The indentation is 2 (two) spaces, for vim you can use vim-ansible-yaml
• Use dict notation, not in-line, this prevents errors later on, example:

bad: this=command

good:
  this: command

• When a module does require '=' parameters, use the following:

moduleX:
  args:
    var: 'something'

• When a module does call something using '=' parameters, use the following:

moduleX: >
  var='something'

• Playbooks should be used for role assignments.
  • Use tagging to call a role:

roles:
  - { role: myrole, tags: ['myrole', 'optional_alias_myrole'] }

• Roles should be used for functional blocks.
  • All templates must contain a {{ ansible_managed }} header.
  • Ensure ansible_managed header is statically set in ansible.cfg or it breaks idempotency.
  • Every role has a self documenting defaults/main.yml file that contains all set-able variables.
  • All variables in the role scope must be named role_variable with the option of spaces being replaced by _ hyphens.
  • The use of dict style variable settings role.variable is discouraged as it complicates overriding.
  • Every variable on a new line for readability.
  • Role must be a complete basic implementation without requiring further variables.
  • Role must be idempotent, meaning: including the role must result in OK, not changed or error when nothing has been changed on the target host.
  • Try to stow everything in main.yml, only use include when it makes sense, which is:
    • when you need to support multiple platforms, then include each in main.yml
  • Use of comments indicate bad code.
• Completeness (especially idempotency) on the target platform is preferred over portability when starting out a new role.
• Don't use: backup: yes, rely on git instead!

General rule for when conditions is that variables do not have to be surrounded like {{ var }}. Below are some general use-cases for when conditions:

• When dealing with multiple suitors for a single condition:

- set_fact:
    hello: 'world'

- name: do task
  command: echo hello world!
  when:
    - hello | intersect( ['world', 'universe'] )

• When dealing with multiple when conditions that need to match in an OR fashion:

- name: do task
  command: echo hello world!
  when:
    - ((skip_install != True) or (ansible_os_family == 'Debian'))

• When dealing with multiple when conditions that need to match in an AND fashion:

- name: do task
  command: echo hello world!
  when:
    - (skip_install != True)
    - (ansible_os_family == 'Debian')
    - (command_result.changed == True)