15. Grouping Hosts and Defining Host Variables in Ansible Inventory

In the previous article, we explored Ansible’s dynamic inventory, which enables flexible management and generation of inventory files. In this tutorial, we focus on using groups and host variables in Ansible’s static inventory files to better organize and manage server configurations.

Introduction to Ansible Inventory

Inventory is one of Ansible’s core concepts—it defines the managed hosts and how Ansible interacts with them. By leveraging inventory effectively, you can group hosts logically and assign specific variables to individual hosts or groups.

Inventory File Formats

Ansible supports multiple inventory file formats, including INI and YAML. Below is an example INI-formatted inventory file:

[web]
web01.example.com
web02.example.com

[db]
db01.example.com
db02.example.com

[production:children]
web
db

[production:vars]
env=production
location=us-west

In this example:

• Two host groups are defined: web and db.
• A parent group named production is created using the :children suffix, containing the web and db subgroups.
• Group-level variables (env and location) are assigned to the production group using the :vars suffix.

Groups and Host Variables

Groups

Groups allow logical organization of hosts. In practice, you might separate web servers, database servers, and other infrastructure components into distinct groups. Ansible supports hierarchical grouping—enabling parent-child relationships for fine-grained control.

Host Variables

Host variables let you define unique configuration parameters for individual hosts—for instance, different SSH users or ports per web server. Example:

[web]
web01.example.com ansible_user=admin ansible_port=2222
web02.example.com ansible_user=ubuntu ansible_port=2200

[db]
db01.example.com ansible_user=dbadmin

Here, web01.example.com and web02.example.com use different SSH users and ports—providing flexibility during task execution.

Using Group Variables

Group variables apply the same configuration across all hosts in a group—for example, security settings or application versions. You can declare them inline using the :vars suffix:

[db:vars]
db_password=SuperSecretPassword

In this case, every host in the db group inherits the db_password variable.

Using Host Variables

Beyond group variables, Ansible lets you assign variables directly to individual hosts within the inventory file—by appending key-value pairs after the hostname:

db01.example.com ansible_user=dbadmin db_host=db01.example.com

Mini Use Case

Consider a simple infrastructure with two web servers and one database server. We want to centralize configuration in the inventory file:

[web]
web01.example.com ansible_user=webuser
web02.example.com ansible_user=webuser

[db]
db01.example.com ansible_user=dbuser db_password=mysecurepassword

[production:children]
web
db

[production:vars]
env=production

Here, both web servers share the same user (webuser), while the database server uses its own dedicated user and password. These variables can then be referenced directly in Ansible playbooks.

Summary

This tutorial covered how to use groups and host variables in Ansible inventory files. Groups provide logical structure for organizing hosts, while host and group variables deliver powerful flexibility—allowing tailored configuration per host or across entire groups. Thoughtful inventory design significantly improves efficiency and maintainability in Ansible-based automation.

In the next article, we’ll introduce Ansible modules—covering common use cases, practical examples, and best practices. Stay tuned!