Dynamic Data Construction in Ansible: Managing Users and Groups

Explore a practical guide on dynamically managing user accounts and groups in Ansible. Learn how to use Jinja2 templates and set_fact for scalable automation.

Dynamically constructing and managing data structures is a crucial skill in Ansible automation, especially for tasks that require flexible and reusable configurations. In this article, we’ll explore this concept using a practical example: managing user accounts and groups on Linux systems.

Scenario: Dynamic User and Group Management

Imagine you have a user_list variable defining multiple users and their associated groups:

``yaml


user_list:
  alice:
    groups:
      - admin
      - developers
  bob:
    groups:
      - developers
  charlie:
    groups:
      - admin
      - qa



Your goal is to:
Dynamically construct a user and group data structure.
Use this structure to manage user accounts and assign them to the appropriate groups.

The Ansible Playbook

Here’s how you can achieve this using set_fact and Jinja2 templating:

`yaml


name: Manage users dynamically
  hosts: localhost
  gather_facts: false
  vars:
    user_list:
      alice:
        groups:
          - admin
          - developers
      bob:
        groups:
          - developers
      charlie:
        groups:
          - admin
          - qa
  tasks:
    - name: Construct user data
      set_fact:
        user_data: >
          {%- set users = [] -%}
          {%- for username, details in user_list.items() -%}
          {{ users.append({'name': username, 'groups': details.groups}) }}
          {%- endfor -%}
          {{ users }}

    - name: Debug constructed user data
      debug:
        var: user_data

    - name: Create users and assign groups
      ansible.builtin.user:
        name: "{{ item.name }}"
        groups: "{{ item.groups | join(',') }}"
      loop: "{{ user_data }}"



Key Components

1. Data Construction with set_fact:

- The set_fact task dynamically builds user_data as a list of dictionaries, each containing:

- name: The username.

- groups: The list of groups.



   Example output:

`yaml


   user_data:
     - name: alice
       groups:
         - admin
         - developers
     - name: bob
       groups:
         - developers
     - name: charlie
       groups:
         - admin
         - qa



2. Dynamic User Management:

- The ansible.builtin.user module iterates through user_data, creating users and assigning them to their respective groups. The groups field is converted to a comma-separated string using join(',').



3. Debugging:

- The debug task ensures that the user_data structure is correct before applying it.



Benefits of This Approach

Dynamic and Reusable:

- Adapts to changes in the input user_list without modifying the playbook logic.


Centralized Logic:

- Data construction is isolated in the set_fact` task, making the playbook easier to read and maintain.

Scalable:

- Handles any number of users and groups effortlessly.

Error Detection:

- Intermediate debugging ensures correctness before execution.

Conclusion

This app