Ansible conditioning, also known as conditional statements, allows you to execute tasks in a playbook based on specific conditions. This feature makes your playbooks more dynamic and adaptable to different environments and scenarios. Conditions are specified using the when keyword.

Using Conditions in Ansible

Conditions in Ansible are typically based on:

• Facts gathered about the host
• Variables
• The results of previous tasks

Basic Syntax

The when keyword is used to define conditions. Here’s the basic syntax:

tasks:
  - name: Install Apache on Debian-based systems
    ansible.builtin.apt:
      name: apache2
      state: present
    when: ansible_facts['os_family'] == "Debian"

Examples of Conditional Statements

Using Facts:

tasks:
  - name: Install Apache on Debian-based systems
    ansible.builtin.apt:
      name: apache2
      state: present
    when: ansible_facts['os_family'] == "Debian"
  - name: Install httpd on RedHat-based systems
    ansible.builtin.yum:
      name: httpd
      state: present
    when: ansible_facts['os_family'] == "RedHat"

Using Variables:

tasks:
  - name: Install a package based on a variable
    ansible.builtin.apt:
      name: "{{ package_name }}"
      state: present
    when: package_name is defined

Combining Multiple Conditions:

tasks:
  - name: Install Apache only on Debian-based systems with specific versions
    ansible.builtin.apt:
      name: apache2
      state: present
    when:
      - ansible_facts['os_family'] == "Debian"
      - ansible_facts['distribution_version'] == "10"

Using the Results of Previous Tasks:

tasks:
  - name: Check if a file exists
    ansible.builtin.stat:
      path: /path/to/file
    register: file_check

  - name: Create the file if it does not exist
    ansible.builtin.file:
      path: /path/to/file
      state: touch
    when: not file_check.stat.exists

Advanced Conditions

You can also use Jinja2 expressions to create more complex conditions:

Checking for Multiple Conditions with Logical Operators:

tasks:
  - name: Ensure the package is installed only if conditions are met
    ansible.builtin.apt:
      name: "{{ package_name }}"
      state: present
    when: (ansible_facts['os_family'] == 'Debian' and ansible_facts['distribution_version'] == '10') or (ansible_facts['os_family'] == 'RedHat' and ansible_facts['distribution_major_version'] == '7')

Using ansible_facts and Variables Together:

tasks:
  - name: Restart Apache if it's running
    ansible.builtin.service:
      name: apache2
      state: restarted
    when: ansible_facts['os_family'] == "Debian" and (ansible_facts['distribution_version'] == "10" or custom_condition == true)

Using failed_when and changed_when

In addition to using conditions for task execution, you can also control the success and failure criteria of a task using failed_when and changed_when:

failed_when:

tasks:
  - name: Check for specific string in a file
    ansible.builtin.command: cat /path/to/file
    register: file_content
    failed_when: "'specific string' not in file_content.stdout"

changed_when:

tasks:
  - name: Ensure a line is in the file
    ansible.builtin.lineinfile:
      path: /path/to/file
      line: "specific line"
    register: line_result
    changed_when: line_result.changed

Other examples

---
- name: Update web servers
  hosts: web
  vars:
    myname: "Rajesh Kumar"

  tasks:
  - name: Install Apache in centos7
    ansible.builtin.yum:
      name: httpd
      state: latest
    when: ( ansible_os_family == "RedHat" and ansible_system == "Linux")
  - name: Copy index.html
    ansible.builtin.copy:
      src: index.html
      dest: /var/www/html/index.html
  - name: Starting a Apache Server
    ansible.builtin.service:
      name: httpd
      state: started
    when: 
      - ansible_os_family == "RedHat"
      - ansible_distribution_major_version == "7"
      - ansible_system == "Linux"
  - name: My Name is Equals to Rajesh Kumar
    debug:
      msg: "My Name is Equals to Rajesh Kumar"
    when: myname == "Rajesh Kumar"
  - name: Ansible print when ubuntu
    debug:
      msg: "I am ubuntu"
    when: ansible_os_family == "Debian"
  - name: My Name is not Equals to Rajesh Kumar
    debug:
      msg: "My Name is not Equals to Rajesh Kumar"
    when: myname != "Rajesh Kumar"

# We can also check if a variable is empty using similar manner.
    - hosts: all
      tasks:
      - shell: cat /etc/temp.txt
        register: output
      - name: Ansible when variable is empty example
        debug:
          msg: "empty"
        when: output.stdout == ""

---
# this is a demo of conditional executions using 'when' statements, which can skip
# certain tasks on machines/platforms/etc where they do not apply.

- hosts: all
  remote_user: root

  vars:
     favcolor: "red"
     dog: "fido"
     cat: "whiskers"
     ssn: 8675309

  tasks:

     - name: "do this if my favcolor is blue, and my dog is named fido"
       shell: /bin/false
       when: favcolor == 'blue' and dog == 'fido'

     - name: "do this if my favcolor is not blue, and my dog is named fido"
       shell: /bin/true
       when: favcolor != 'blue' and dog == 'fido'

     - name: "do this if my SSN is over 9000"
       shell: /bin/true
       when: ssn > 9000

     - name: "do this if I have one of these SSNs"
       shell: /bin/true
       when:  ssn in [ 8675309, 8675310, 8675311 ]

     - name: "do this if a variable named hippo is NOT defined"
       shell: /bin/true
       when: hippo is not defined

     - name: "do this if a variable named hippo is defined"
       shell: /bin/true
       when: hippo is defined

For Ubuntu

- name: Update web servers
  hosts: web
  vars:
    myname: "Rajesh Kumar"

  tasks:
  - name: Install Apache in ubuntu
    ansible.builtin.apt:
      name: apache2
      state: latest
    when: ( ansible_os_family == "Debian" and ansible_system == "Linux")
  - name: Copy index.html
    ansible.builtin.copy:
      src: index.html
      dest: /var/www/html/index.html
  - name: Starting a Apache Server
    ansible.builtin.service:
      name: apache2
      state: started
    when: 
      - ansible_os_family == "Debian"
      - ansible_distribution_major_version == "20"
      - ansible_system == "Linux"
  - name: My Name is Equals to Rajesh Kumar
    debug:
      msg: "My Name is Equals to Rajesh Kumar"
    when: myname == "Rajesh Kumar"
  - name: Ansible print when ubuntu
    debug:
      msg: "I am ubuntu"
    when: ansible_os_family == "Debian"
  - name: My Name is not Equals to Rajesh Kumar
    debug:
      msg: "My Name is not Equals to Rajesh Kumar"
    when: myname != "Rajesh Kumar"