Ansible Modules

In this article, we explore a variety of Ansible modules categorized by their functionality. Each module group is tailored for specific tasks such as system management, command execution, file handling, database operations, cloud interactions, and Windows management.

Modules are grouped as follows:

• System Modules: Perform actions at the operating system level, such as managing users and groups, configuring IP tables and firewalls, handling logical volumes, managing mount operations, and controlling services (start, stop, restart).
• Command Modules: Allow execution of commands or scripts on a host. Use the command module for simple commands or the expect module for interactive commands. The script module lets you run local scripts on remote hosts.
• File Modules: Facilitate operations on files, including setting file permissions with ACL, compression with archive/unarchive, and file content modifications using modules like find, lineinfile, and replace.
• Database Modules: Manage database operations for systems such as MongoDB, MySQL, MS SQL, and PostgreSQL, allowing you to add, remove, or update configurations.
• Cloud Modules: Offer robust functionalities for various cloud providers including Amazon, Azure, Docker, Google, OpenStack, and VMware. They help manage tasks like instance creation/destruction, networking, security configurations, container management, and data center operations.
• Windows Modules: Optimize management of Windows environments. Modules like win_copy, win_command, win_service, and others help with tasks ranging from file transfer to installing software and managing Windows services.

For a complete reference and detailed documentation, please visit the Ansible Documentation.

Let's delve into some specific modules to understand how to utilize them and read their documentation pages.

The Command Module

The command module executes a command on a remote node using key-value pair parameters. Below is an example playbook that runs the date command and displays the contents of /etc/resolv.conf:

- name: Play 1
  hosts: localhost
  tasks:
    - name: Execute command 'date'
      command: date

    - name: Display resolv.conf contents using full path
      command: cat /etc/resolv.conf

    - name: Display resolv.conf contents using change directory
      command: cat resolv.conf chdir=/etc

    - name: Create folder if it does not exist
      command: mkdir /folder creates=/folder

Notice how parameters such as chdir and creates modify the execution behavior. The chdir parameter changes the working directory before executing the command, while the creates parameter prevents command execution if a specific file or directory already exists.

One important concept is "free form" input. In the command module, the command itself (e.g., cat /etc/resolv.conf or mkdir /folder) is provided as a free form string. In contrast, modules like the copy module require explicit parameter names:

- name: Play 1
  hosts: localhost
  tasks:
    - name: Copy file from source to destination
      copy:
        src: /source_file
        dest: /destination

The Script Module

The script module facilitates executing a local script on remote nodes. When invoked, Ansible automatically transfers the script from the controller machine to the target nodes and then runs it. This automation simplifies tasks that require script execution across multiple machines.

Simply specify the local path of the script and include any necessary arguments.

The Service Module

The service module manages system services, enabling you to start, stop, or restart them. Below is an example playbook to start a database service:

- name: Start Services in order
  hosts: localhost
  tasks:
    - name: Start the database service using key-value format
      service: name=postgresql state=started

You can also express the same logic using a dictionary format for enhanced readability:

- name: Start Services in order
  hosts: localhost
  tasks:
    - name: Start the database service using a map
      service:
        name: postgresql
        state: started

In these examples, the name parameter identifies the service (in this case, PostgreSQL), and the state parameter declares the desired state. The use of "started" instead of "start" ensures that if the service is already running, Ansible performs no extra action, promoting idempotency.

The Lineinfile Module

The lineinfile module is essential for managing file content. It ensures that a specific line is present in a file by adding or replacing it as needed, making it highly useful for configuration management. For example, to add a new DNS server entry to /etc/resolv.conf:

- name: Add DNS server to resolv.conf
  hosts: localhost
  tasks:
    - name: Ensure the correct nameserver is present in resolv.conf
      lineinfile:
        path: /etc/resolv.conf
        line: 'nameserver 10.1.250.10'

In contrast, a shell script appending text to a file might create duplicate entries over multiple executions:

# Sample script
echo "nameserver 10.1.250.10" >> /etc/resolv.conf

Repeated executions of the script could result in multiple lines, while the lineinfile module guarantees a single, idempotent entry.

Summary Table of Ansible Module Categories

This concludes our detailed walkthrough of essential Ansible modules. To extend your knowledge, explore Ansible’s comprehensive documentation and practice these modules in real-world scenarios.

For more detailed information, visit the official Ansible Documentation.

See you in the next lesson!