Ansible/Playbooks

Overview

The Ansible documentation has a nice overview of playbooks: https://docs.ansible.com/ansible/latest/user_guide/playbooks_intro.html

Brief Notes

Playbooks

• playbooks are a way of executing commands on remote machines in a scripted way
• can orchestrate multiple ordered processes
• playbooks are written in YAML
• each playbook can contain one or more plays
• each play will target different servers (maybe all of them, maybe just web servers, maybe just db servers)
• user specifies hosts - remote machines on which Ansible will run commands
• users - the remote user is the user that Ansible will run the particular task as

Tasks

• each play has a list of tasks associated with it
• tasks are executed in order on all machines that match the host pattern
• ansible completes the task on all remote machines before it moves on to the next task

Handlers

• handlers are "conditional tasks" - tasks that are triggered by other tasks
• the handlers are triggered once at the end of each block of tasks - this keeps them from being restarted over and over by a set of related tasks

Roles

• Roles are just a way of automatically loading variables, tasks, and task handlers.
• Roles use a known file structure to load appropriate vars/tasks/handlers
• A given play will specify a list of roles in the playbook - this indicates that ansible should look for variables/tasks/handlers that match up with those roles, and add them to the play
• Roles can be dependent on other roles (that's the purpose of the "meta" yaml file)

Example:

• the following playbook entry will automatically populate the play with a list of variables, tasks, and handlers from the roles subdirectory
• the roles subdirectory will contain two subdirectories, common and web, with files for those roles

---
# playbook.yml
- name: example play
  hosts: webservers
  roles:
   - common
   - web

Tags

• Tags are a way of only running part of your playbook
• Think of tags as a filtering operation

Idempotence

• idempotent means you can run it multiple times with the same outcome as running it one time
• modules should check whether the desired final state has already been achieved, and exit without doing anything if so

Example: Secure Nginx Server

Ansible/Nginx Playbook - a page that walks through two example playbooks

• Example 1: nginx server playbook
• Example 2: secure nginx server playbook

Full Stack Example: Django Celery RabbitMQ Postgres

Ansible/Full Stack Playbook - a page that walks through a playbook for a full stack example