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Ansible Essentials Cheatsheet

A concise guide to Ansible, covering essential concepts, commands, and best practices for automating infrastructure and application deployment. Includes playbook structure, module usage, and task management.

Getting Started with Ansible

Installation & Setup

Install Ansible:

pip install ansible

Verify Installation:

ansible --version

Configure Hosts File (/etc/ansible/hosts):
Define your managed hosts or groups.

[webservers]
192.168.1.101
192.168.1.102

[dbservers]
192.168.1.103

SSH Key Configuration:
Ensure passwordless SSH access to managed hosts.

ssh-keygen -t rsa -N '' -f ~/.ssh/id_rsa
ssh-copy-id [email protected]

Basic Commands

ansible -m ping all

Verify connectivity to all managed hosts.

ansible -m shell -a 'uptime' webservers

Execute the uptime command on the webservers group.

ansible-playbook playbook.yml

Run an Ansible playbook.

Ansible Configuration File

The Ansible configuration file (ansible.cfg) allows you to customize Ansible’s behavior. Common settings include:

  • inventory: Path to the inventory file.
  • remote_user: Default user for SSH connections.
  • private_key_file: Path to the SSH private key.
[defaults]
inventory = /path/to/inventory
remote_user = ansible
private_key_file = ~/.ssh/id_rsa
host_key_checking = False

Playbook Essentials

Playbook Structure

A playbook is a YAML file containing one or more plays. Each play defines tasks to be executed on a set of hosts.

---  # Playbook Start
- hosts: webservers
  become: true  # Equivalent to sudo
  tasks:
    - name: Ensure Apache is installed
      apt:
        name: apache2
        state: present
    - name: Start Apache service
      service:
        name: apache2
        state: started

Tasks

name

A descriptive name for the task.

module

The Ansible module to be executed (e.g., apt, service, copy).

args

Parameters for the module.

become

Escalate privileges (sudo).

become_user

Specify the user for privilege escalation.

register

Store the task’s output in a variable.

Handlers

Handlers are tasks that are only run when notified by another task. They are typically used for restarting services after configuration changes.

tasks:
  - name: Modify Apache config
    copy:
      src: httpd.conf
      dest: /etc/apache2/apache2.conf
    notify: Restart Apache

handlers:
  - name: Restart Apache
    service:
      name: apache2
      state: restarted

Variables & Templates

Defining Variables

Variables can be defined in several places:

  • Inventory file: Host-specific or group-specific variables.
  • Playbook: Using the vars section.
  • Included files: Using vars_files.
  • Command line: Using the -e option.
vars:
  http_port: 80
  max_clients: 200

tasks:
  - name: Set Apache port
    lineinfile:
      path: /etc/apache2/ports.conf
      regexp: '^Listen '
      line: 'Listen {{ http_port }}'

Variable Precedence

Ansible uses a specific order of precedence when resolving variables. From highest to lowest:

  1. Command line (-e)
  2. Role variables (roles/role_name/vars/main.yml)
  3. Playbook vars section
  4. Inventory group vars
  5. Inventory host vars
  6. group_vars/all and host_vars/* files

Templates

Templates allow you to dynamically generate configuration files using Jinja2 templating. They are useful for customizing configurations based on variables.

Listen {{ http_port }}
<VirtualHost *:{{ http_port }}>
  ServerName {{ ansible_hostname }}
  DocumentRoot /var/www/html
</VirtualHost>

tasks:
  - name: Deploy Apache virtual host
    template:
      src: vhost.conf.j2
      dest: /etc/apache2/sites-available/000-default.conf
    notify: Restart Apache

Advanced Features

Roles

Roles are a way to organize and reuse Ansible code. A role typically includes tasks, handlers, variables, and templates.

ansible-galaxy init my_role

Directory structure:

my_role/
├── defaults/
│   └── main.yml
├── handlers/
│   └── main.yml
├── meta/
│   └── main.yml
├── tasks/
│   └── main.yml
├── templates/
└── vars/
    └── main.yml

Includes

include_tasks

Include a list of tasks from another file.

include_vars

Include variables from another file.

import_tasks

Statically include a task list at playbook parse time.

Conditionals

Tasks can be conditionally executed using when clauses. This allows you to run tasks only when certain conditions are met.

tasks:
  - name: Install package on Debian
    apt:
      name: package_name
      state: present
    when: ansible_os_family == 'Debian'
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