What is an Ansible Playbook?
An Ansible Playbook is a YAML file used to define and execute automation tasks on remote machines. It is the heart of Ansible configuration management, enabling infrastructure as code. Playbooks can describe a policy to be enforced or a set of steps in a general IT process.
Unlike scripts that run sequentially, Playbooks are declarative, meaning you define the desired state of your system rather than how to get there.
Structure of an Ansible Playbook
An Ansible Playbook is made up of:
- Plays: Each play targets a group of hosts and defines a list of tasks to run.
- Tasks: Each task executes a module with specific arguments.
- Modules: Reusable Ansible code blocks like
apt,copy,service, etc. - Variables: Used to store dynamic values.
- Handlers: Special tasks triggered by
notifyfrom other tasks. - Roles: A way to organize playbooks into reusable components.
Example: A Basic Ansible Playbook
---
- name: Install Apache on web servers
hosts: webservers
become: yes
vars:
apache_package: apache2
tasks:
- name: Update apt cache
apt:
update_cache: yes
- name: Install Apache
apt:
name: "{{ apache_package }}"
state: present
- name: Ensure Apache is running
service:
name: "{{ apache_package }}"
state: started
enabled: yes
Explanation:
hosts: webservers: Target all machines in thewebserversgroup.become: yes: Run tasks withsudoprivileges.vars: Define reusable variables.tasks: A list of actions to perform.
Handlers Example
Handlers are tasks triggered only when notified by another task (used for things like restarting services).
- name: Configure Nginx
hosts: nginx
become: yes
tasks:
- name: Copy nginx config
copy:
src: nginx.conf
dest: /etc/nginx/nginx.conf
notify: Restart nginx
handlers:
- name: Restart nginx
service:
name: nginx
state: restarted
Using Variables
Variables can be defined in the playbook, inventory, or external files.
vars:
app_user: deploy
app_port: 8080
And then used like:
- name: Add application user
user:
name: "{{ app_user }}"
Real-world Playbook with Multiple Plays
---
- name: Install Docker on all hosts
hosts: all
become: yes
tasks:
- name: Install Docker dependencies
apt:
name: "{{ item }}"
state: present
loop:
- apt-transport-https
- ca-certificates
- curl
- software-properties-common
- name: Add Docker GPG key
apt_key:
url: https://download.docker.com/linux/ubuntu/gpg
state: present
- name: Add Docker repository
apt_repository:
repo: deb https://download.docker.com/linux/ubuntu focal stable
state: present
- name: Install Docker
apt:
name: docker-ce
state: present
- name: Deploy App Container
hosts: appservers
become: yes
tasks:
- name: Run nginx container
docker_container:
name: nginx
image: nginx:latest
state: started
ports:
- "80:80"
Best Practices
- Use roles to organize playbooks.
- Keep playbooks idempotent (safe to run multiple times).
- Use variables and templates to make playbooks dynamic.
- Use handlers to avoid unnecessary restarts.
- Always test in staging before applying to production.
Summary Table of Key Components
| Component | Description | Example |
|---|---|---|
hosts | Group of machines to run the playbook on | hosts: webservers |
tasks | Steps to be performed on the remote machines | apt, copy, service |
vars | Define variables used in tasks | app_port: 8080 |
handlers | Tasks triggered by notify | Restart services |
roles | Reusable and modular directories of playbooks | roles/webserver/tasks/main.yml |
become | Run tasks with sudo privileges | become: yes |
loop | Iterate over a list | loop: [pkg1, pkg2] |