working-with-playbooks.md

Playbooks

Ansible Playbook

• Primary means of:
  • Configuration management
  • Deploying applications
  • Provisioning
  • Orchestration
• A sequence of tasks

Ansible Playbooks

cd $INTRO_ANSIBLE_DIR/working-with-playbooks

.
├── ansible.cfg
├── hosts
├── static-site.yml
├── templates
│   ├── index.html.j2
│   └── mysite.conf.j2
└── Vagrantfile

Name	Type	Description
static-site.yml	file	Ansible playbook
files	directory	Artefacts to be placed on remote host
templates	directory	Templates that will be rendered and uploaded to remote host

Ansible Playbook Structure

• A playbook is a YAML file containing a list of plays
• A play is a dictionary object

  <ul><li>
          <code style="color:red;">key</code><code>: </code><code style="color:blue;">value</code>
      </li></ul>
  

• Some keys in a play may contain dictionaries or lists

Ansible Playbook Structure

• A play must contain:
  • hosts
    • A string representing a particular host or group of hosts
      • hosts: localhost
      • hosts: app.mywebsite.com
      • hosts: appserver
    • These are what you will configure

Ansible Playbook Structure

• A play may optionally contain:
  • tasks
    • A list of dictionaries
    • What you want to do
  • name
    • Description of the play
  • vars
    • Variables scoped to the play

Structure of a Task

• A task is a dictionary object containing
  • name
    • Describes what the task does
    • Optional but best practice to use
  • module
    • Dictionary object
    • Key represents Python module which will perform tasks
    • May have arguments

Structure of a Task

• Two styles of module object in tasks
  • string form
  • dictionary form
• Dictionary form is more suitable for complex arguments
• Matter of preference/style

Create a new VM

vagrant up --provider virtualbox

• This creates an Ubuntu VM
• Additional ports for a static website
  • 80 (HTTP)
  • 443 (HTTPS)

Deploy and configure an application

• static-site.yml performs following actions
  • Installs nginx package
  • Templates our nginx config (templates/mysite.conf.j2)
  • Renders template file (templates/index.html.j2) and place it on host
  • Re/Starts nginx

Run our first playbook

ansible-playbook static-site.yml

Visit the static site once playbook has finished.

Privilege Escalation

• Some tasks we need to perform require sudo privileges on target machine
• The become attribute tells Ansible to run tasks as a certain user
  • By default this is sudo
  • Specify user with become_user

  
    - name: Set up static website with nginx
       hosts: myserver
       become: true
       tasks:
   

• Can be in play or task scope
• Accepts yes or true (no or false are implicit)

Ansible Abstraction Layer

• We have used both yum and apt to install packages in previous exercises, respectively
• Some automation tools abstract common functions from different operating systems
  • Eg. package to abstract package managers from various OS
• Ansible has a thin abstraction layer
  • On Debian/Ubuntu use apt module
  • On Centos use yum module

Idempotent Behaviour

• It is sometimes necessary to run configuration/deploy tools more than once
  • Debugging
  • Temporary issues (eg. loss of network)
• Can be problematic if operations not prepared to manage repetition
  • Unmanaged duplication
  • Errors caused by violating unique constraints

Idempotent Behaviour

• Most Ansible modules aim to be idempotent
• Can be run repeatedly and will only change once
• Output of each task indicates when target action resulted in a change
  • ok : Already in desired state; Ansible did not change anything
  • changed : Ansible changed to desired state
• Makes behaviour declarative

Exercise: Idempotent Behaviour

• Log into your VM and remove some files

  vagrant ssh
  sudo rm -f /usr/share/nginx/html/index.html /etc/nginx/sites-available/mysite.conf
  

• Run the static-site-fail.yml playbook
• Remove fail task and run again

Summary

• Use Ansible Playbook to run complex tasks
• Playbook consists of array of YAML dictionaries called plays
• Each play contains array of tasks that are executed on remote host