Master Ansible Variables: Naming Rules, Scopes, and Practical Playbook Examples

Variable Naming Rules

Variables must start with a letter and can contain only letters, numbers, and underscores.

Variable Scopes

Ansible supports three scopes:

Global : defined on the command line with the -e option.

Play : defined inside a playbook using vars or vars_files.

Host/Group : defined in the inventory file, host_vars, or group_vars directories.

Global Variables

Example playbook using a global variable package to install Apache:

---
- name: Install Apache
  hosts: servera
  tasks:
    - name: Install {{ package }}
      apt:
        name: "{{ package }}"
        state: present

Run with:

ansible-playbook test.yml -e "package=apache2"

Play Variables

Define a variable directly in a play:

---
- name: Create User
  hosts: servera
  vars:
    user: jack
  tasks:
    - name: Create a user named {{ user }}
      user:
        name: "{{ user }}"

Run the playbook to see the variable substituted.

Variable Files

Create a separate YAML file (e.g., user.yml):

---
user: jerry

Import it with vars_files:

---
- name: Create User
  hosts: servera
  vars_files:
    - user.yml
  tasks:
    - name: Create a user named {{ user }}
      user:
        name: "{{ user }}"

Host Variables

Add a variable to a host entry in the inventory:

serverb user=user1

[web]
servera

[prod:children]
web

Reference the variable in the playbook the same way as other variables.

Host‑Vars Directory

Create a host_vars directory and a file named after the host (e.g., servera.yml) containing:

---
user: user2

The playbook will automatically load this variable for the matching host.

Group Variables

Define a variable for a group in the inventory:

[web:vars]
user=user3

Or create a group_vars directory with a file named after the group (e.g., web.yml) containing:

---
user: user4

Playbooks targeting the group will use the defined variable.