Introduction

While Ansible provides a vast library of built-in modules to automate various tasks, there are cases where users may need to create custom modules to meet specific requirements. Custom modules allow users to extend Ansible's functionality and automate tasks that are not covered by existing modules. In this article, we'll explore the process of writing custom modules in Ansible.

Creating a Custom Module

Custom modules in Ansible are written in Python and follow a specific structure. A custom module typically consists of the following components:

1. Module File: This is the main Python script that defines the logic of the module. It includes functions for processing module arguments, executing tasks on managed nodes, and returning results to Ansible.

2. Module Documentation: Custom modules should include documentation that describes the module's purpose,

input parameters, and expected output. This documentation follows the Ansible module documentation format.

1. Module Utilities (Optional): Depending on the complexity of the module, additional utility functions or classes may be included to handle specific tasks.

Example: Custom Ansible Module to Manage Custom Application

Let's create a custom Ansible module named custom_app to manage a custom application. This module will include functions to start, stop, and check the status of the application.

custom_app.py:

#!/usr/bin/python

from ansible.module_utils.basic import AnsibleModule

def start_app():
    # Logic to start the custom application
    return "Custom application started successfully"

def stop_app():
    # Logic to stop the custom application
    return "Custom application stopped successfully"

def check_status():
    # Logic to check the status of the custom application
    return "Custom application is running"

def main():
    module = AnsibleModule(argument_spec={})
    result = {}

    action = module.params.get('action')

    if action == 'start':
        result['msg'] = start_app()
    elif action == 'stop':
        result['msg'] = stop_app()
    elif action == 'status':
        result['msg'] = check_status()
    else:
        module.fail_json(msg='Invalid action specified')

    module.exit_json(**result)

if __name__ == '__main__':
    main()

Using the Custom Module

Once the custom module is created, it can be used like any other Ansible module in playbooks or ad-hoc commands.

Example Playbook:

---
- name: Manage Custom Application
  hosts: all
  tasks:
    - name: Start Custom Application
      custom_app:
        action: start

    - name: Stop Custom Application
      custom_app:
        action: stop

    - name: Check Status of Custom Application
      custom_app:
        action: status

Conclusion

Writing custom modules in Ansible allows users to extend Ansible's functionality and automate tasks tailored to their specific requirements. By following the guidelines for creating custom modules and leveraging the flexibility of Python, users can create powerful and customized automation solutions with Ansible.