Master Ansible Playbooks: Core Components, Variables, Loops & Handlers

Playbooks Overview

Playbooks are a powerful component of Ansible for configuration management, allowing execution of multiple tasks based on text files and repeatable runs. They use YAML (Yet Another Markup Language), a semi‑structured, declarative language with high readability and easy interaction with scripts.

Core Components

Tasks: task definitions

Variables: variable definitions

ansible_ssh_port: specify SSH port

ansible_ssh_user: specify SSH user

ansible_ssh_pass: SSH login password (plain text)

ansible_sudo_pass: sudo password

Inventory Example

[webserver]
172.16.36.70 ansible_ssh_port=22 ansible_ssh_user=root ansible_ssh_pass=zhenping.me

Inventory Parameters

Common parameters placed after a host in the inventory include template (template file), Handles (handlers), and Roles (role definitions for orchestrating different playbooks).

YAML Syntax

All data structures are indicated by indentation and can be nested. Each line is a key:value pair separated by a colon; multiple pairs on one line use {} and commas. Lists are marked with -. Example:

- hosts: webserver
  remote_user: root
  tasks:
    - name: install nginx
      yum: name=nginx state=present
    - name: start nginx
      service: name=nginx state=started enabled=true
    - name: install php-fpm
      yum: name=php-fpm state=present
    - name: start php-fpm
      service: name=php-fpm state=started enabled=true
  vars: {}
  handlers: []
- hosts: dbserver
  remote_user: root
  tasks:
    - name: install mysql
      yum: name=mysql state=present

Variables

Variable names consist of letters, numbers, and underscores and must start with a letter. Types include:

Facts : automatically gathered host attributes, available without explicit declaration.

Custom variables : defined by the user, e.g., via

ansible-playbook test.yml --extra-vars "hosts=www user=zhenping"

or through roles.

Host variables : defined after a host entry in the inventory and apply to that host only.

Group variables : defined for a group in the inventory, e.g.:

[webserver]
172.16.36.70
172.16.36.60
[webserver:vars]
var1=value
var2=value

Passing Variables from the Command Line

ansible-playbook script.yml --extra-vars "username=ubunt"
ansible-playbook script.yml -e VARS

Conditional Tests

Adding a when clause after a task enables conditional execution; the when statement supports Jinja2 syntax. Example (install only on RedHat families):

- hosts: webserver
  remote_user: root
  tasks:
    - name: yum install keepalived
      yum: name=keepalived state=present
      when: ansible_os_family == "RedHat"
    - name: say hello
      shell: /bin/echo "hello world"

Loops (Iteration)

Use the built‑in item variable with with_items to iterate over a list.

- hosts: webserver
  remote_user: root
  tasks:
    - name: user add
      user: name={{ item }} state=present
      with_items:
        - testuser1
        - testuser2
        - testuser3
        - testuser4

Complex items can be dictionaries:

- hosts: webserver
  remote_user: root
  tasks:
    - name: user add
      user: name={{ item.name }} state=present group={{ item.groups }}
      with_items:
        - { name: 'tom2', groups: 'tom' }
        - { name: 'tom2', groups: 'tom2' }

Handlers (Triggers)

Handlers are tasks that run only when notified by other tasks, typically after a change such as a configuration file update.

- hosts: webserver
  remote_user: root
  tasks:
    - name: yum install nginx
      yum: name=nginx state=present
    - name: start nginx
      service: name=nginx state=started enabled=true
    - name: copy configuration file
      copy: src=/etc/nginx/nginx.conf dest=/etc/nginx/nginx.conf
      notify: restart nginx
  handlers:
    - name: restart nginx
      service: name=nginx state=reloaded