Day03 - harishgorla5/Ansible GitHub Wiki

Handlers, Templates, Loops, and Roles

🔁 1. Handlers – What, Why, and How

✅ What is a Handler?

A handler is a special task that only runs when explicitly notified by another task.

✅ Why Use Handlers?

Avoid restarting services unnecessarily. Instead, only restart if something actually changed — like config files.

✅ How Handlers Work

A task uses notify: <handler-name>
If the task causes a change, Ansible queues the handler
Handlers are run at the end of the play (not immediately)

🔧 Example:

- name: Copy configuration file
  copy:
    src: my.cnf
    dest: /etc/my.cnf
  notify: Restart MariaDB

handlers:
  - name: Restart MariaDB
    service:
      name: mariadb
      state: restarted

🧩 2. Jinja2 Templates – Full Explanation

✅ What is Jinja2?

A template language that allows:

Variable substitution: {{ var }}
Control structures: {% if %}, {% for %}
Filters: {{ var | lower }}, {{ list | join(',') }}

✅ Purpose in Ansible:

To generate dynamic config files based on host-specific data.

📄 Example Template: `index.html.j2`

<h1>Hello from {{ inventory_hostname }}</h1>
{% if ansible_distribution == "Amazon" %}
<p>This is Amazon Linux.</p>
{% endif %}

📥 Example Playbook:

- name: Deploy homepage
  template:
    src: index.html.j2
    dest: /var/www/html/index.html

🔁 3. Loops – Repeating Tasks

✅ Why Loops?

To repeat a task for each item in a list — like creating users, installing packages, etc.

📘 Syntax:

- name: Create users
  user:
    name: "{{ item }}"
    state: present
  loop:
    - alice
    - bob
    - carol

📦 4. Roles – Organized Reusable Ansible Content

✅ Why Use Roles?

To structure and reuse code for tasks like installing Apache, setting up MariaDB, etc.

🧱 Role Structure

apache/
├── tasks/main.yml
├── handlers/main.yml
├── templates/index.html.j2
├── vars/main.yml

🔧 Generate Role:

ansible-galaxy init apache

🔧 Use Role in Playbook:

- name: Setup Apache
  hosts: web
  become: true
  roles:
    - apache

🧪 Real-World Use Case: Deploy LAMP Stack Using All Concepts

💡 Goal:

Install Apache with dynamic homepage using template
Install MariaDB using role
Use handlers to restart services on config change
Use loops to add system users

📁 Directory Layout

project/
├── inventory
├── site.yml
├── roles/
│   ├── apache/
│   │   ├── tasks/main.yml
│   │   ├── templates/index.html.j2
│   │   └── handlers/main.yml
│   └── mariadb/
│       ├── tasks/main.yml
│       ├── templates/my.cnf.j2
│       └── handlers/main.yml

🔸 Example: roles/apache/tasks/main.yml

- name: Install Apache
  yum:
    name: httpd
    state: present

- name: Deploy dynamic homepage
  template:
    src: index.html.j2
    dest: /var/www/html/index.html
  notify: Restart Apache

🔸 roles/apache/handlers/main.yml

- name: Restart Apache
  service:
    name: httpd
    state: restarted

🔸 roles/apache/templates/index.html.j2

<h1>Hello from {{ inventory_hostname }}</h1>
<p>Powered by Ansible</p>

🔸 roles/mariadb/tasks/main.yml

- name: Install MariaDB
  yum:
    name: mariadb-server
    state: present

- name: Deploy DB config
  template:
    src: my.cnf.j2
    dest: /etc/my.cnf
  notify: Restart MariaDB

🔸 roles/mariadb/handlers/main.yml

- name: Restart MariaDB
  service:
    name: mariadb
    state: restarted

🔸 site.yml (Main Playbook)

- name: Configure Web Server
  hosts: web
  become: true
  roles:
    - apache

- name: Configure DB Server
  hosts: db
  become: true
  roles:
    - mariadb

- name: Add system users
  hosts: all
  become: true
  tasks:
    - name: Create users
      user:
        name: "{{ item }}"
        state: present
      loop:
        - dev
        - qa
        - ops

✅ Summary: What You Practiced Today

Concept	Real Use
Handlers	Restart httpd/mariadb on config change
Jinja2	Dynamic HTML and config file templates
Loops	User creation and package installs
Roles	Reusable, modular playbooks