Ansible Inventory: Static, Dynamic & Advanced Patterns (Complete Guide)

By Luca Berton · Published 2024-01-01 · Category: database-automation

Complete guide to Ansible inventory. Configure static INI and YAML inventories, dynamic inventory scripts, AWS/Azure/GCP plugins, host patterns, group.

The inventory defines what hosts Ansible manages and how to connect to them. It can be a simple INI file, YAML, a dynamic script pulling from cloud APIs, or a combination of all three.

Static Inventory (INI Format)

# inventory.ini

# Ungrouped hosts
mail.example.com

# Web servers
[webservers]
web1.example.com
web2.example.com
web3.example.com ansible_port=2222

# Database servers
[dbservers]
db1.example.com
db2.example.com

# Group of groups
[production:children]
webservers
dbservers

# Group variables
[webservers:vars]
http_port=80
ansible_user=deploy

[production:vars]
env=production
monitoring=true

Range Patterns

[webservers]
web[01:50].example.com     # web01 through web50

[dbservers]
db-[a:f].example.com       # db-a through db-f

Static Inventory (YAML Format)

# inventory.yml
all:
  children:
    production:
      children:
        webservers:
          hosts:
            web1.example.com:
              http_port: 80
            web2.example.com:
              http_port: 8080
          vars:
            ansible_user: deploy
        
        dbservers:
          hosts:
            db1.example.com:
              db_port: 5432
            db2.example.com:
              db_port: 5432
          vars:
            ansible_user: dbadmin
      
      vars:
        env: production
        monitoring: true
    
    staging:
      children:
        staging_web:
          hosts:
            staging-web1.example.com:
        staging_db:
          hosts:
            staging-db1.example.com:
      vars:
        env: staging

Host and Group Variables

Directory Structure (Recommended)

inventory/
├── hosts.yml              # Main inventory
├── group_vars/
│   ├── all.yml            # Variables for ALL hosts
│   ├── webservers.yml     # Variables for webservers group
│   ├── dbservers.yml      # Variables for dbservers group
│   └── production/
│       ├── vars.yml       # Production variables
│       └── vault.yml      # Encrypted production secrets
└── host_vars/
    ├── web1.example.com.yml
    └── db1.example.com.yml

# group_vars/all.yml
---
ntp_server: ntp.example.com
dns_servers:
  - 8.8.8.8
  - 8.8.4.4

# group_vars/webservers.yml
---
http_port: 80
max_connections: 1000
ssl_enabled: true

# host_vars/web1.example.com.yml
---
http_port: 8080  # Override for this host
ssl_cert: /etc/ssl/web1.pem

Dynamic Inventory

AWS EC2

# aws_ec2.yml
plugin: amazon.aws.aws_ec2
regions:
  - us-east-1
  - eu-west-1
filters:
  tag:Environment: production
  instance-state-name: running

keyed_groups:
  - key: tags.Role
    prefix: role
  - key: placement.region
    prefix: aws_region
  - key: instance_type
    prefix: type

hostnames:
  - tag:Name
  - private-ip-address

compose:
  ansible_host: private_ip_address

# Use dynamic inventory
ansible-playbook -i aws_ec2.yml site.yml

# Test / list hosts
ansible-inventory -i aws_ec2.yml --list
ansible-inventory -i aws_ec2.yml --graph

Azure

# azure_rm.yml
plugin: azure.azcollection.azure_rm
include_vm_resource_groups:
  - production-rg
auth_source: auto

keyed_groups:
  - key: tags.role | default('untagged')
    prefix: role
  - key: location
    prefix: azure_region

hostnames:
  - name
  - private_ipv4_addresses

GCP

# gcp_compute.yml
plugin: google.cloud.gcp_compute
projects:
  - my-gcp-project
zones:
  - us-central1-a
  - us-east1-b
filters:
  - status = RUNNING
auth_kind: serviceaccount
service_account_file: /path/to/sa.json

keyed_groups:
  - key: labels.env
    prefix: env

Custom Script

#!/usr/bin/env python3
# custom_inventory.py
import json
import sys

def get_inventory():
    return {
        "webservers": {
            "hosts": ["web1.example.com", "web2.example.com"],
            "vars": {"http_port": 80}
        },
        "dbservers": {
            "hosts": ["db1.example.com"],
            "vars": {"db_port": 5432}
        },
        "_meta": {
            "hostvars": {
                "web1.example.com": {"ansible_host": "10.0.0.1"},
                "web2.example.com": {"ansible_host": "10.0.0.2"},
                "db1.example.com": {"ansible_host": "10.0.0.10"}
            }
        }
    }

if __name__ == '__main__':
    if '--list' in sys.argv:
        print(json.dumps(get_inventory(), indent=2))
    elif '--host' in sys.argv:
        print(json.dumps({}))

chmod +x custom_inventory.py
ansible-playbook -i custom_inventory.py site.yml

Multiple Inventory Sources

# Combine static + dynamic
ansible-playbook -i inventory/static.yml -i inventory/aws_ec2.yml site.yml

# Use inventory directory
ansible-playbook -i inventory/ site.yml  # Reads all files in directory

Host Patterns

# All hosts
ansible all -m ping

# Specific group
ansible webservers -m ping

# Multiple groups (OR)
ansible 'webservers:dbservers' -m ping

# Intersection (AND)
ansible 'webservers:&production' -m ping

# Exclusion (NOT)
ansible 'production:!dbservers' -m ping

# Wildcards
ansible 'web*.example.com' -m ping

# Regex
ansible '~web[0-9]+\.example\.com' -m ping

# Specific host
ansible web1.example.com -m ping

# Index
ansible 'webservers[0]' -m ping      # First host
ansible 'webservers[-1]' -m ping     # Last host
ansible 'webservers[0:3]' -m ping    # First 3 hosts

Useful Commands

# List all hosts
ansible-inventory -i inventory.yml --list

# Show host graph
ansible-inventory -i inventory.yml --graph

# Show vars for a host
ansible-inventory -i inventory.yml --host web1.example.com

# Verify connectivity
ansible all -i inventory.yml -m ping

# Run ad-hoc command
ansible webservers -i inventory.yml -m command -a "uptime"

Best Practices

Use YAML format — more readable than INI for complex inventories
Use group_vars/ and host_vars/ — separate variables from host lists
Encrypt secrets with Vault — group_vars/production/vault.yml
Use dynamic inventory for cloud — keeps inventory in sync automatically
Tag-based grouping — use keyed_groups with cloud tags
One source of truth — don't duplicate hosts across files
Test with ansible-inventory --graph — verify structure before running

FAQ

What is Ansible inventory?

The inventory is a file or script that lists the hosts Ansible manages, organized into groups. It defines connection parameters (IP, user, port) and variables. It can be a static file (INI/YAML) or dynamic (pulling from AWS, Azure, etc.).

What is the difference between static and dynamic inventory?

Static inventory is a manually maintained file (INI or YAML). Dynamic inventory is a script or plugin that queries an external source (cloud API, CMDB, LDAP) at runtime to generate the host list automatically.

Where is the default inventory file?

/etc/ansible/hosts is the default. Override with -i inventory.yml on the command line or inventory = ./inventory.yml in ansible.cfg.

How do I use group variables?

Create group_vars/.yml files next to your inventory. Variables defined there automatically apply to all hosts in that group. Use group_vars/all.yml for variables that apply everywhere.

How do I test if inventory is working?

Run ansible-inventory -i inventory.yml --graph to see the host structure, then ansible all -i inventory.yml -m ping to test connectivity.

Conclusion

INI or YAML — YAML preferred for complex inventories
group_vars/ + host_vars/ — organize variables cleanly
Dynamic inventory plugins — AWS, Azure, GCP, VMware
Host patterns — webservers:&production:!dbservers for precise targeting
ansible-inventory --graph — always verify your inventory structure

Category: database-automation

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