Ansible Basic Concepts

Core Components

Control Node

Machine where Ansible is installed
Executes playbooks and commands
Must run Linux/Unix
Cannot be a Windows host

Managed Nodes (Hosts)

Systems managed by Ansible
No agent installation required
Needs Python installed
Can be any OS

Inventory

Static list of managed nodes:

# inventory.ini
[webservers]
web1.example.com
web2.example.com

[dbservers]
db1.example.com
db2.example.com

[all:vars]
ansible_user=deploy

Modules

Modules are units of code that perform specific tasks:

# Example module usage
- name: Ensure Apache is installed
  apt:
    name: apache2
    state: present

- name: Copy file
  copy:
    src: /src/file
    dest: /dest/file

Tasks

Individual units of work:

tasks:
  - name: Install package
    apt:
      name: nginx
      state: present

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

Playbooks

YAML files containing tasks and configurations:

---
- name: Configure webserver
  hosts: webservers
  become: true

  tasks:
    - name: Install nginx
      apt:
        name: nginx
        state: present

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

Key Concepts

Idempotency

Running a playbook multiple times should result in the same outcome:

# Idempotent task
- name: Create directory
  file:
    path: /app/data
    state: directory
    mode: '0755'

# Non-idempotent task (avoid)
- name: Create directory
  command: mkdir /app/data

Facts

System information gathered by Ansible:

- name: Display facts
  debug:
    msg: "OS: {{ ansible_os_family }}, Memory: {{ ansible_memtotal_mb }}MB"

Variables

Store and reuse values:

vars:
  http_port: 80
  max_clients: 200

tasks:
  - name: Configure port
    template:
      src: nginx.conf.j2
      dest: /etc/nginx/nginx.conf

Handlers

Tasks triggered by changes:

tasks:
  - name: Copy configuration
    copy:
      src: nginx.conf
      dest: /etc/nginx/nginx.conf
    notify: Restart nginx

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

Templates

Jinja2 templates for dynamic files:

# nginx.conf.j2
server {
    listen {{ http_port }};
    server_name {{ server_name }};

    location / {
        root {{ web_root }};
    }
}

Command Line Tools

ansible

Run ad-hoc commands:

# Execute command on all hosts
ansible all -i inventory -m command -a "uptime"

# Install package on webservers
ansible webservers -i inventory -m apt -a "name=nginx state=present"

ansible-playbook

Execute playbooks:

# Run playbook
ansible-playbook -i inventory site.yml

# Run with variables
ansible-playbook -i inventory site.yml -e "version=1.2.3"

ansible-vault

Manage encrypted content:

# Create encrypted file
ansible-vault create secrets.yml

# Edit encrypted file
ansible-vault edit secrets.yml

# Encrypt existing file
ansible-vault encrypt vars.yml

Working with Roles

Role Structure

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

Using Roles

---
- hosts: webservers
  roles:
    - common
    - webserver