Here’s a comprehensive tutorial on all the ways to define and use variables in Ansible inventory/hosts, covering every major approach—including their best use cases and clear examples for each.

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Complete Guide: All Ways to Define Variables in Ansible Inventory/Hosts

Ansible variables make playbooks and roles flexible and dynamic. Variables can be defined in multiple ways, with different precedence and scopes: per host, per group, globally, in YAML, in INI, or in directory structures.

Below, we’ll cover every method with examples.

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1. Host Variables in Inventory File (Host Vars)

Define variables directly for a single host in the INI inventory file:

[webservers]
web1 ansible_host=192.168.1.101 http_port=80 max_clients=200
web2 ansible_host=192.168.1.102 http_port=8080 max_clients=150

Usage in playbook/task:

- name: Show host vars
  hosts: webservers
  tasks:
    - debug: msg="Host {{ inventory_hostname }} uses port {{ http_port }} and max clients {{ max_clients }}"
Code language: JavaScript (javascript)

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2. Group Variables in Inventory File (Group Vars)

Define variables for all hosts in a group in the INI inventory:

[dbservers]
db1 ansible_host=192.168.1.201
db2 ansible_host=192.168.1.202

[dbservers:vars]

db_port=3306 backup_window=02:00

All hosts in [dbservers] get db_port and backup_window.

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3. Global (All) Group Vars

Set variables for all hosts by using the [all:vars] section in your INI inventory:

[all:vars]
env=production
admin_email=admin@example.com

All hosts will inherit these.

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4. Using YAML Inventory (hosts.yml)

YAML-style inventory files let you define hosts, groups, and variables in a structured way:

all:
  vars:
    datacenter: DC1
  children:
    webservers:
      hosts:
        web1:
          ansible_host: 192.168.1.101
          http_port: 80
        web2:
          ansible_host: 192.168.1.102
          http_port: 8080
      vars:
        nginx_version: 1.24
    dbservers:
      hosts:
        db1:
        db2:
      vars:
        db_port: 3306
Code language: CSS (css)

Usage in playbook: Variables are accessed as usual ({{ db_port }} etc).

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5. Host and Group Variable Files (host_vars & group_vars Directory)

This is the most powerful and recommended way for larger projects.

Directory structure:

inventory/
  hosts        # inventory file (can be INI or YAML)
  group_vars/
    all.yml    # applies to all hosts
    webservers.yml
    dbservers.yml
  host_vars/
    web1.yml
    db1.yml
Code language: PHP (php)

Example:

• inventory/group_vars/webservers.yml: http_port: 80 nginx_version: 1.23
• inventory/host_vars/web1.yml: http_port: 8080

All hosts in webservers get http_port=80, except web1 (overrides to 8080).

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6. Nested Groups and Variables (children keyword in YAML)

You can nest groups, with vars defined for parent or child groups:

all:
  children:
    frontend:
      hosts:
        web1:
        web2:
      vars:
        tier: frontend
    backend:
      hosts:
        db1:
        db2:
      vars:
        tier: backend
  vars:
    env: production

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7. Dynamic Inventory with Variables

Dynamic inventory scripts/plugins (e.g., for AWS) can return host/group variables as part of their JSON:

{
  "webservers": {
    "hosts": ["web1", "web2"],
    "vars": {
      "http_port": 80
    }
  },
  "_meta": {
    "hostvars": {
      "web1": {"nginx_version": "1.24"},
      "web2": {"nginx_version": "1.22"}
    }
  }
}
Code language: JSON / JSON with Comments (json)

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8. Using vars in Playbooks, Roles, and Tasks

You can define variables directly in a playbook, though these are not inventory variables:

- hosts: webservers
  vars:
    http_port: 8080
    max_clients: 100
  tasks:
    - debug: msg="Port is {{ http_port }}"
Code language: JavaScript (javascript)

• Note: These override inventory vars (except for host_vars and group_vars, which have higher precedence).

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9. Extra Vars (-e) at Command Line

Highest precedence!

ansible-playbook -i inventory/hosts site.yml -e "env=staging http_port=8081"
Code language: JavaScript (javascript)

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10. Environment Variables

You can access environment variables with lookup('env', 'ENV_VAR_NAME') in your playbooks.
These are not inventory vars, but often used for secrets.

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11. Facts as Variables

Ansible facts (collected via setup module) are accessible as variables (e.g. ansible_hostname, ansible_distribution).

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Precedence: Which Variables Override Which?

(Highest to lowest):

1. Extra vars (-e)
2. Task/block vars
3. Role vars
4. Play vars
5. Host vars (from host_vars/ or inventory)
6. Group vars (from group_vars/ or inventory)
7. All group vars ([all:vars] or group_vars/all.yml)
8. Playbook/inventory defaults
9. Facts

See Ansible docs: Variable precedence

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Quick Reference Table

Method	Example Syntax / Path	Scope	Example Value
Host vars in INI	web1 ansible_host=1.2.3.4	One host	web1 ansible_host=1.2.3.4
Group vars in INI	[group:vars] key=value	All group hosts	[web:vars] port=80
All group vars	[all:vars] key=value	All hosts	[all:vars] env=prod
YAML inventory vars	vars: block	Any host/group	vars: {foo: bar}
group_vars/ dir	group_vars/webservers.yml	All group hosts	nginx_version: 1.24
host_vars/ dir	host_vars/web1.yml	One host	http_port: 8080
Playbook vars	vars: in play	All play hosts	vars: {debug: true}
Extra vars	-e "foo=bar"	All play hosts	CLI only
Dynamic inventory JSON	hostvars/vars keys	From dynamic source	AWS, GCP plugins, etc.
Environment vars (lookup)	lookup('env', 'VAR')	Local to playbook	e.g. AWS keys

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Examples:

A. group_vars/webservers.yml

nginx_version: 1.25
Code language: CSS (css)

B. host_vars/web1.yml

http_port: 8088
Code language: HTTP (http)

C. INI Inventory with Group Vars

[appservers]
app1 ansible_host=1.2.3.10
app2 ansible_host=1.2.3.11

[appservers:vars]

app_env=staging

D. YAML Inventory with Group/Host Vars

all:
  children:
    monitoring:
      hosts:
        zabbix1:
          zabbix_agent_port: 10050

E. Dynamic Inventory

Returned by AWS/GCP inventory plugins, includes host/group vars.

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Summary

• Host vars: Specific to one host, defined in inventory, host_vars/, or dynamic inventory.
• Group vars: For a whole group, defined in inventory, group_vars/, or dynamic inventory.
• All group vars: Apply to all hosts.
• YAML inventory: Clean, scalable, supports all of the above.
• Directory structure (group_vars/, host_vars/): Recommended for big projects.
• Extra vars: For overrides and quick changes.
• Dynamic inventory: Great for cloud, VMs, auto-scaling.
• Precedence matters! The closer to the CLI, the more powerful.

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Best Practice

• Use group_vars/ and host_vars/ directories for maintainable, scalable automation.
• For dynamic environments (cloud), use dynamic inventory + host/group vars returned as JSON.
• Reserve extra vars (-e) for CI/CD or special cases.

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