1. Introduction

Ansible is an open-source automation tool for configuration management, application deployment, and task automation. It uses a simple YAML-based language (called Playbooks) and operates agentlessly over SSH or WinRM.

2. Why Ansible?

✅ Agentless: No software/agent installation needed on clients.
✅ Simple YAML Syntax: Easy to learn and write.
✅ Idempotency: Ensures operations are safe and repeatable.
✅ Large Community: Extensive module support and reusable roles via Ansible Galaxy.
✅ Scalable: Works for small systems to complex infrastructures.

3. Core Concepts

Controller Node: The machine where Ansible is installed and run.
Managed Nodes: Remote systems Ansible manages.
Inventory: A file that lists managed hosts.
Modules: Reusable scripts (e.g., copy, yum, service).
Playbooks: YAML files that define a set of plays/tasks.
Roles: Predefined directory structure for organizing Playbooks.

4. Ansible Architecture

+-------------------+
|  Ansible Control  |
|      Node         |
+--------+----------+
         |
         | SSH / WinRM
         v
+--------+----------+
|   Managed Nodes   |
| (Linux / Windows) |
+-------------------+

5. Installation

On Ubuntu/Debian:

sudo apt update
sudo apt install ansible -y

On CentOS/RHEL:

sudo yum install epel-release -y
sudo yum install ansible -y

Via pip:

pip install ansible

6. Ansible Inventory

Default location: /etc/ansible/hosts

Example (INI):

[web]
web1.example.com
web2.example.com

[db]
db1.example.com ansible_user=admin ansible_port=2222

YAML Inventory (new-style):

all:
  hosts:
    server1:
    server2:
  children:
    web:
      hosts:
        server1:
    db:
      hosts:
        server2:

7. Modules

Ansible ships with hundreds of modules.

Examples:

Module	Purpose
`ping`	Check connectivity
`copy`	Copy files
`yum` / `apt`	Install packages
`service`	Manage services
`user`	Manage users

Example:

ansible all -m ping

8. Ad-Hoc Commands

Quick tasks without a playbook.

ansible web -m shell -a "uptime"
ansible db -m yum -a "name=httpd state=latest"

9. Playbooks

Written in YAML format.

Example:

- name: Install Nginx
  hosts: web
  become: yes
  tasks:
    - name: Install nginx
      apt:
        name: nginx
        state: present

    - name: Start nginx
      service:
        name: nginx
        state: started
        enabled: yes

Run with:

ansible-playbook nginx.yml

10. Roles

Standardized directory structure:

roles/
└── nginx/
    ├── tasks/
    │   └── main.yml
    ├── handlers/
    ├── templates/
    ├── files/
    ├── vars/
    └── defaults/

Use in playbook:

roles:
  - nginx

11. Variables and Facts

Defining Variables:

In playbooks: vars
From files: vars_files
From inventory
Gathered facts (system info)

vars:
  pkg_name: nginx

tasks:
  - name: Install web server
    apt:
      name: "{{ pkg_name }}"
      state: present

12. Templates (Jinja2)

Dynamic file generation.

Example: nginx.conf.j2:

server {
  listen 80;
  server_name {{ server_name }};
}

Usage in playbook:

- name: Template config
  template:
    src: nginx.conf.j2
    dest: /etc/nginx/nginx.conf

13. Conditionals and Loops

Conditionals:

- name: Install Nginx
  apt:
    name: nginx
    state: present
  when: ansible_os_family == "Debian"

Loops:

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

14. Handlers and Notifications

tasks:
  - name: Change config
    template:
      src: nginx.conf.j2
      dest: /etc/nginx/nginx.conf
    notify:
      - restart nginx

handlers:
  - name: restart nginx
    service:
      name: nginx
      state: restarted

15. Tags

Run specific tasks only.

- name: Install nginx
  apt:
    name: nginx
    state: present
  tags: install

Run with:

ansible-playbook site.yml --tags install

16. Error Handling

- name: Try something
  command: /bin/false
  ignore_errors: yes

Or use block, rescue, always:

- block:
    - name: Fail
      command: /bin/false
  rescue:
    - name: Recover
      debug:
        msg: "Something went wrong"

17. Vault (Secrets Management)

Encrypt secrets like passwords.

ansible-vault encrypt secrets.yml
ansible-vault decrypt secrets.yml
ansible-playbook site.yml --ask-vault-pass

18. Best Practices

Use roles to organize code.
Don’t hardcode passwords or IPs.
Use version control (e.g., Git).
Group similar hosts.
Test with --check.

19. Ansible Galaxy

A repository of community-maintained roles.

ansible-galaxy install geerlingguy.nginx