Playbooks

• Expressed in YAML format. Aim is to be human readable with a minimum of syntax.
• Composed of 'plays' in a list
• Plays operate on hosts and execute tasks on them
• Plays run in the order specified in the playbook - top to bottom

Basics

• hosts line is a list of one or more groups or host patterns. Can select the order in which the hosts are run from some predefined choices.
• remote_user is the name of the user account - can also be defined per task
• Tasks List - executed in order against all machines matched by the host pattern.
• Handlers - Notify is triggered once at the end of each block of tasks in a play. If nothing notifies a handler then it will not run. Handlers can listen to topics and tasks notify these topics. This is useful for 3rd party roles to decouple handlers from their names - as if two handlers exist with the same name then only one will be run.
• Can run playbook with --syntax-check flag to verify that playbok is syntactically correct.
• Ansible uses Jinja2 templating e.g. "NaN"
• Before running tasks Ansible will gather facts about the system it is to provision. These begin with ansible_ and are globally available to use anywhere that variables can be used.

Reusable playbooks

• import - static - preprocessed at playbook parsing time
• include - dynamic - processed at runtime when task is encountered
• include is better for looping as the task will be executed once for each item in the loop
• include limitations - tags and tasks don't show up in list output. Can't notify a handler which only exists in a dynamic include
• import limitations - loops cannot be used. Variables from inventory sources cannot be used.

Commands

• import_playbooks, include_playbooks
• import_tasks, include_tasks
• import_roles, include_roles

Variables

• Can be defined in playbooks and roles
• Facts are variables that are discovered, not set by the user - fact gathering can be turned off if not needed. Can add user supplied facts using facts.d.
• Don't use names that conflict with attributes and methods of Python dictionaries
• Can use register to save the result of a module into a variable. These are then valid for the remainder of the playbook run.
• Can use external variables file to separate sensitive variables from rest of source
• Extra variables can be passed on the command line using --extra-vars.

Conditionals

• when: clauses can be used to conditionally execute tasks
• This takes a raw Jinja2 expression without the curly braces

Loops

• Can use loop: tag with a list
• Can use query to return the list
• Can use do until loops to handle retries
• Can use register to capture all output from the loop
• Ansible sets the variable item for each iteration of the loop