Variables

Hard‑coding values in playbooks makes them rigid. Variables allow you to write reusable, dynamic automation. You can define variables in many places – playbooks, inventory, files, or even from command line.

Defining Variables in a Playbook

Use the vars section in a play:

---
- name: Use variables
  hosts: all
  vars:
    package_name: nginx
    service_name: nginx
  tasks:
    - name: Install {{ package_name }}
      apt:
        name: "{{ package_name }}"
        state: present
    - name: Start {{ service_name }}
      service:
        name: "{{ service_name }}"
        state: started

Variable substitution uses double curly braces: {{ variable_name }}.

Variable Precedence

Variables can be defined in many places. The order of precedence (from lowest to highest) includes: inventory group vars, inventory host vars, playbook vars, extra vars (-e). In general, the last defined wins.

Inventory Variables

You can define variables per host or per group in the inventory file:

[webservers]
web1 ansible_host=192.168.1.10 http_port=8080

[webservers:vars]
nginx_version=1.18

Passing Variables from Command Line

Override any variable with --extra-vars or -e:

ansible-playbook playbook.yml -e "package_name=apache2"

Using Variables from Files

You can include a file containing variables:

vars_files:
  - vars/common.yml
  - vars/{{ ansible_os_family }}.yml

Registering Output as Variables

You can capture a task’s output into a variable using register:

- name: Get uptime
  command: uptime
  register: uptime_result

- name: Print uptime
  debug:
    msg: "Uptime is {{ uptime_result.stdout }}"

Two Minute Drill

Variables make playbooks reusable.
Define in vars, inventory, vars_files, or command line (-e).
Use {{ variable }} for substitution.
Register task output with register.

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