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General

  • YAML files - All yaml files should use 2 space indents and end with .yml
  • Variables - Use jinja variable syntax over deprecated variable syntax. {{ var }} not $var
  • Use spaces around jinja variable names. {{ var }} not {{var}}
  • Variables that are environment specific and that need to be overridden should be in ALL CAPS.
  • Variables that are internal to the role should be lowercase.
  • Prefix all variables defined in a role with the name of the role. Example: EDXAPP_FOO
  • Keep roles self contained - Roles should avoid including tasks from other roles when possible
  • Plays should do nothing more than include a list of roles except where pre_tasks and post_tasks are required (to manage a load balancer for example)
  • Plays/Playbooks that apply to the general community should be copied to configuration/playbooks
  • Plays/Playbooks that apply only to a specific organization (edx-east, edx-west) should be copied to a sub-directory under configuration/playbooks
  • Handlers - Do not use handlers. If you need to restart an app when specific tasks run, just add a task to do so at the end of the playbook. If necessary, it can be skipped with tags (see Role Life-cycle)
  • Separators - Use underscores (e.g. my_role) not dashes (my-role).
  • Paths - When defining paths, do not include trailing slashes (e.g. my_path: /foo not my_path: /foo/. When concatenating paths, follow the same convention (e.g. {{ my_path }}/bar not {{ my_path }}bar)

Conditionals and Return Status

  • Always use when: for conditionals - To check if a variable is defined when: my_var is defined or when: my_var is not defined

  • To verify return status (see conditionals)

     - command: /bin/false
    register: my_result
    ignore_errors: True
  - debug: msg="task failed"
    when: my_result|failed

Formatting

  • Use yaml-style blocks.
    Good:

      - file:
      dest: "{{ test }}"
	  src: "./foo.txt"
	  mode: 0770 
	  state: present
	  user: "root"
	  group: "wheel"

    Bad:

    - file: >
	dest={{ test }} src=./foo.txt mode=0770
	state=present user=root group=wheel

  • Break long lines using yaml line continuation.
    Reference: http://docs.ansible.com/playbooks_intro.html

    - shell: >
	python a very long command --with=very --long-options=foo
	--and-even=more_options --like-these

Roles

Role Variables

  • "common" role - Contains tasks that apply to all roles that are edX specific.
  • "common_vars" role - Contains vars that apply to all roles that are edX specific.
  • Roles variables - Variables specific to a role should be defined in /vars/main.yml. All variables should be prefixed with the role name.
  • Role defaults - Default variables should configure a role to install edx in such away that all services can run on a single server
  • Variables that are environment specific and that need to be overridden should be in all caps.

  • Every role should have a standard set of role directories, example that includes a python and ruby virtualenv:

    edxapp_data_dir: "{{ COMMON_DATA_DIR }}/edxapp"
edxapp_app_dir: "{{ COMMON_APP_DIR }}/edxapp"
edxapp_log_dir: "{{ COMMON_LOG_DIR }}/edxapp"
edxapp_venvs_dir: "{{ edxapp_app_dir }}/venvs"
edxapp_venv_dir: "{{ edxapp_venvs_dir }}/edxapp"
edxapp_venv_bin: "{{ edxapp_venv_dir }}/bin"
edxapp_rbenv_dir: "{{ edxapp_app_dir }}"
edxapp_rbenv_root: "{{ edxapp_rbenv_dir }}/.rbenv"
edxapp_rbenv_shims: "{{ edxapp_rbenv_root }}/shims"
edxapp_rbenv_bin: "{{ edxapp_rbenv_root }}/bin"
edxapp_gem_root: "{{ edxapp_rbenv_dir }}/.gem"
edxapp_gem_bin: "{{ edxapp_gem_root }}/bin"

Role Naming Conventions

  • Role names - Terse, one word if possible, use underscores if necessary.
  • Role task names - Terse, descriptive, spaces are OK and should be prefixed with the role name.

Secure vs. Insecure data

As a general policy we want to protect the following data:

  • Usernames
  • Public keys (keys are OK to be public, but can be used to figure out usernames)
  • Hostnames
  • Passwords, API keys

Directory structure for the secure repository:


ansible
├── files
├── keys
└── vars

The default secure_dir is set in group_vars/all and can be overridden by adding another file in group_vars that corresponds to a deploy group name.

For templates or files that are secure use first_available_file, example:

- name: xserver | install read-only ssh key for the content repo that is required for grading
  copy:
    src: "{{ item }}"
    dest: /etc/git-identity
    force: yes
    owner: ubuntu
    group: adm
    mode: "0640"
  first_available_file:
    - "{{ secure_dir }}/files/git-identity"
    - "git-identity-example"
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