Ansible Conditional Statements allow the user to manage the execution of tasks based on specific conditions. The primary mechanism by which conditional logic is added to tasks in Ansible is by using the when keyword.
These allow tasks to run only when specific criteria are met such as variable values, file presence, or system facts. This ensures selective task execution, improves playbook flexibility, and supports robust automation.
Syntax
IF expressions are introduced by the keyword when followed by an expression whose value is either true or false; if the value is true, then an action is performed, and otherwise, it isn't done.
Example:
- name: Print message when condition is met
debug:
msg: "This task runs only if the condition is true"
when: some_condition
Expressions
The condition in a when statement can be a simple variable, a comparison, or a more complex expression involving logical operators such as and, or, and not.
Example:
- name: Print message if variable is true
debug:
msg: "The variable is true"
when: example_var
- name: Print message if both conditions are true
debug:
msg: "Both conditions are true"
when: var1 and var
- name: Print message if either condition is true
debug:
msg: "At least one condition is true"
when: var1 or var2
Combining Conditions
- Logical operators will allow you to combine multiple conditions in order to form a very complicated conditional statement.
Example:
- name: Complex condition
debug:
msg: "Complex condition met"
when: var1 and (var2 or var3)
Registered Variables
Tasks can register variables that store the results of their execution. The registered variables can then be used within conditional statements, in which decisions are taken based on the output of previous tasks.
Example:
- name: Check if a file exists
stat:
path: /path/to/file
register: file_status
- name: Print message if file exists
debug:
msg: "The file exists"
when: file_status.stat.exists
Process for using Conditional Statements
Step 1: Launch EC2 Instance
- Go to AWS Console and login with credentials.
- Navigate to EC2 Dashboard and launch ec2 instance.
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Step 2: Install Ansible
Now install ansible in our local machine by using following command.
sudo amazon-linux-extras install ansible2-1024.png)
Step 3: Define Inventory file or Host
- Here we have provided the inventory variable on the host file.
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Step 4: Create Playbook
Define Variables
- Variables are essential for storing values that can be reused throughout your playbook. You can define variables in several places, including inventory files, playbooks, roles, and extra variables passed from the command line.
- name: Example Playbook with Variables
hosts: localhost
vars:
example_var: true
tasks:
- name: Print variable value
debug:
var: example_var
Use when Keyword
- When keyword is used to specify the condition that must be true for the task to run. Conditions can be based on variable values or expressions.
- name: Example Playbook with Conditional Statements
hosts: localhost
vars:
is_debug: true
tasks:
- name: Print debug message
debug:
msg: "Debug mode is enabled"
when: is_debug
Use Logical Operators
- You can use logical operators (and, or, not) to combine multiple conditions in a single when statement, creating more complex conditions.
- name: Example Playbook with Complex Conditions
hosts: localhost
vars:
var1: true
var2: false
tasks:
- name: Print message if both conditions are true
debug:
msg: "Both conditions are true"
when: var1 and var2
- name: Print message if either condition is true
debug:
msg: "At least one condition is true"
when: var1 or var2
Use Registered Variables
- Registered variables capture the results of tasks and can be used in subsequent tasks. They are created using the register keyword.
- name: Example Playbook with Registered Variables
hosts: localhost
tasks:
- name: Check if a file exists
stat:
path: /path/to/file
register: file_status
- name: Print message if file exists
debug:
msg: "The file exists"
when: file_status.stat.exists
Combine All Concepts
- Combine variables, when keyword, logical operators, and registered variables to create a comprehensive playbook with dynamic task execution.
Example:
- name: Comprehensive Playbook with Conditional Statements
hosts: localhost
vars:
var1: true
var2: false
file_path: "/path/to/file"
tasks:
- name: Check if the file exists
stat:
path: "{{ file_path }}"
register: file_status
- name: Print message if both conditions are true
debug:
msg: "Both conditions are true"
when: var1 and var2
- name: Print message if file exists
debug:
msg: "The file exists"
when: file_status.stat.exists
- name: Print message if either condition is true
debug:
msg: "At least one condition is true or the file exists"
when: var1 or var2 or file_status.stat.exists
Step 5: Run Playbook
- Now run playbook by using ansible-playbook commands
- Two tasks were skipped because their conditions evaluated to false
- The path specified in your variable file was "/path/to/file", which likely does not exist.
Example 2
- Now change file path to see different result
var1: true
var2: true
file_path: "/etc/hosts" # Assuming this file exists on your system
- Run the playbook again to see different results.
Here we see all tasks are executed.