6.0 - Ansible Modules¶

06.1 - Ansible Modules¶

Notes¶

Modules are categorised based on functionalities e.g
System - Commands based on the host system e.g. start/stop service
Commands - Used to execute commands or scripts on hosts
Files - Used to execute file-specific commands e.g. find, copy, replace
Database - Used to interact with databases such as MongoDB, MSSQL, MySQL
Cloud - Used to interact with cloud providers like AWS, Azure, GCP, Linode, Digital Ocean.
Windows - Commands to help use Ansible in a windows environment, be it working with files, user management, executing commands.
This is a non-exhaustive list - many more modules can be viewed in the Ansible documentation, with details on how to use each provided.

Command¶

Used to execute a command on a remote node
Parameters include:

Example Playbook:

Example playbook to execute the date command and run the cat command on a desired file.

Creates parameter is used to perform a check if the folder or file exists before running the command
chdir requests that ansible changes directory before the command is ran
free_form - the command module takes a free form command to run; no parameters are required
Not all commands support free-form parameters, example, copy requires a source and target dir to be specified.

Script¶

Used to run a local script on a remote node after transferring it.
Example playbook:

Service¶

Used to manage services on the system e.g. stop, start, restart
Example playbooks for this can be done in one of two manners:

Question: Why write the state as "started" and not "start"?
Not instructing ansible to start the service, we are asking ansible to ensure that it is started i.e. if it's not started - start it
This leads to the idempotency of ansible modules:
- Idempotency - An operation is idempotent if the result of performing it once is exactly the same as the result of performing it repeatedly without any intervening actions
In general, Ansible's idea is to be able to run a playbook, when running it again, everything should return "as expected", if not, Ansible will make it so.

Lineinfile¶

Searches for a line in a file and replaces it or adds it if it doesn't exist
Example playbook:

Note that this action IN THEORY could be achieved by running a script like this:

However, this would repeatedly add the same entry to /etc/resolv.conf rather than replace it or not add it if found. By contrast the idempotency of Ansible means that if this task is ran as part of a playbook, the entry is added once and only once if it's not found.

6.2 - Introduction to Plugins¶

Overview¶

Ansible plugins aim to provide additional functionality and customisation options beyond the core features.
Plugins extend or modify the core functionality of ansible, such as inventory, modules, and callbacks.
Plugins can be found as any of:
Inventory Plugins (e.g. Dynamic Inventory)
Module Plugins (e.g. provision custom cloud configuration)
Action Plugins (e.g. define a series of high-level tasks to help enhance consistency in the configuration)
Callback Plugins - provide hooks into ansible's execution lifecycle, facilitating custom actions during playbook execution.
Lookup Plugins (typically used with Databases)
Filter Plugins
Connection Plugins
Each plugin comes with their own parameters and configuration.

6.3 - Modules and Plugins Index¶

Overview¶

The module and plugin index aims to act as a hub for searching plugins and modules to be added to playbooks.
Each comes with documentation for usage, examples, and additional supporting documentation.
Index link
The index offers:
Search and filtering
Detailed documentation per plugin
Version compatability guidance and considerations
Community contributions for support and contribution guidance.

06.2 - Ansible Modules Coding Exercises¶

Notes¶

Q1¶

Update the playbook with a play to Execute a script on all web server nodes. The script is located at /tmp/install_script.sh

Use the Script module

- name: 'Execute a script on all web server nodes'
  hosts: web_nodes
  tasks:
  - name: 'Execute a script on all web server nodes'
    script: /tmp/install_script.sh

Q2¶

Update the playbook to add a new task to start httpd services on all web nodes

Use the Service module

-
    name: 'Execute a script on all web server nodes'
    hosts: web_nodes
    tasks:
        -
            name: 'Execute a script on all web server nodes'
            script: /tmp/install_script.sh
        - name: 'start http services on all web server nodes'
          service:
            name: httpd
            state: started

Q3¶

Update the playbook to add a new task in the beginning to add an entry into /etc/resolv.conf file for hosts. The line to be added is nameserver 10.1.250.10

Note: The new task must be executed first, so place it accordingly.

Use the Lineinfile module

-
    name: 'Execute a script on all web server nodes'
    hosts: web_nodes
    tasks:
        - name: 'Add enntry to /etc/resolv.conf file'
          lineinfile:
            path: /etc/resolv.conf
            line: 'nameserver 10.1.250.10'
        -
            name: 'Execute a script'
            script: /tmp/install_script.sh
        -
            name: 'Start httpd service'
            service:
                name: httpd
                state: present

Q4¶

Update the playbook to add a new task at second position (right after adding entry to resolv.conf) to create a new web user.

Use the user module for this. User details to be used are given below:Username: web_useruid: 1040group: developers

-
    name: 'Execute a script on all web server nodes and start httpd service'
    hosts: web_nodes
    tasks:
        -
            name: 'Update entry into /etc/resolv.conf'
            lineinfile:
                path: /etc/resolv.conf
                line: 'nameserver 10.1.250.10'
        - name: 'add user web_user'
          user:
            name: web_user
            uid: 1040
            group: developers

        -   name: 'Execute a script'
            script: /tmp/install_script.sh
        -
            name: 'Start httpd service'
            service:
                name: httpd
                state: present