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Conditionals and Loops

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In this section, we will explore how to use conditionals and loops in Ansible playbooks. These features allow you to create more dynamic and flexible automation scripts.

Conditionals

Conditionals in Ansible allow you to execute tasks based on certain conditions. This is useful when you want to perform actions only if specific criteria are met.

Basic Syntax

The basic syntax for conditionals in Ansible is to use the when keyword followed by a Jinja2 expression.

- name: Install Apache on Debian-based systems
  apt:
    name: apache2
    state: present
  when: ansible_os_family == "Debian"

Practical Example

Let's consider a more detailed example where we install different packages based on the operating system.

- name: Install web server
  hosts: all
  tasks:
    - name: Install Apache on Debian-based systems
      apt:
        name: apache2
        state: present
      when: ansible_os_family == "Debian"

    - name: Install Apache on RedHat-based systems
      yum:
        name: httpd
        state: present
      when: ansible_os_family == "RedHat"

Common Mistakes

  • Incorrect Condition Syntax: Ensure that the condition is a valid Jinja2 expression.
  • Indentation Errors: Make sure the when keyword is correctly indented under the task.

Loops

Loops in Ansible allow you to repeat a task multiple times with different parameters. This is useful for tasks like installing multiple packages or creating multiple users.

Basic Syntax

The basic syntax for loops in Ansible is to use the loop keyword followed by a list of items.

- name: Install multiple packages
  apt:
    name: "{{ item }}"
    state: present
  loop:
    - apache2
    - mysql-server
    - php

Practical Example

Let's consider a more detailed example where we create multiple users.

- name: Create multiple users
  hosts: all
  tasks:
    - name: Add users
      user:
        name: "{{ item.name }}"
        state: present
        groups: "{{ item.groups }}"
      loop:
        - { name: 'alice', groups: 'admin' }
        - { name: 'bob', groups: 'users' }
        - { name: 'charlie', groups: 'users' }

Loop Control

You can also control the behavior of loops using loop_control.

- name: Install multiple packages with index
  apt:
    name: "{{ item }}"
    state: present
  loop:
    - apache2
    - mysql-server
    - php
  loop_control:
    index_var: pkg_index

Common Mistakes

  • Incorrect Loop Syntax: Ensure that the loop is a valid list.
  • Variable Scope: Be cautious about variable scope within loops.

Practical Exercise

Exercise

Write a playbook that performs the following tasks:

  1. Installs nginx on Debian-based systems and httpd on RedHat-based systems.
  2. Creates three users: user1, user2, and user3, each belonging to the users group.

Solution

- name: Conditional and Loop Exercise
  hosts: all
  tasks:
    - name: Install web server on Debian-based systems
      apt:
        name: nginx
        state: present
      when: ansible_os_family == "Debian"

    - name: Install web server on RedHat-based systems
      yum:
        name: httpd
        state: present
      when: ansible_os_family == "RedHat"

    - name: Create multiple users
      user:
        name: "{{ item }}"
        state: present
        groups: users
      loop:
        - user1
        - user2
        - user3

Summary

In this section, we covered:

  • The use of conditionals with the when keyword to execute tasks based on specific conditions.
  • The use of loops with the loop keyword to repeat tasks with different parameters.
  • Practical examples and common mistakes to avoid.

Understanding conditionals and loops will help you create more dynamic and flexible Ansible playbooks. In the next section, we will delve into roles, which allow you to organize your playbooks into reusable components.

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