Ansible Inventory Management Guide

# inventory/hosts.ini

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

[dbservers]
db1.example.com
db2.example.com

[loadbalancers]
lb1.example.com

[production:children]
webservers
dbservers
loadbalancers

[production:vars]
ansible_user=deploy
ansible_ssh_private_key_file=~/.ssh/deploy_key

# inventory/hosts.yml
all:
  children:
    production:
      children:
        webservers:
          hosts:
            web1.example.com:
            web2.example.com:
            web3.example.com:
              ansible_port: 2222
          vars:
            http_port: 80
            app_env: production

        dbservers:
          hosts:
            db1.example.com:
              postgresql_max_connections: 200
            db2.example.com:
              postgresql_max_connections: 100
          vars:
            db_port: 5432

        loadbalancers:
          hosts:
            lb1.example.com:

      vars:
        ansible_user: deploy
        ansible_ssh_private_key_file: ~/.ssh/deploy_key

inventory/
  hosts.yml
  group_vars/
    all.yml           # Variables for all hosts
    webservers.yml    # Variables for webservers group
    dbservers.yml     # Variables for dbservers group
    production.yml    # Variables for production group
  host_vars/
    web1.example.com.yml   # Variables for specific host
    db1.example.com.yml

---
ntp_servers:
  - 0.pool.ntp.org
  - 1.pool.ntp.org
timezone: Europe/Rome
admin_email: ops@example.com

---
http_port: 80
https_port: 443
document_root: /var/www/html
nginx_worker_processes: auto

---
# This host has extra memory, can handle more connections
nginx_worker_connections: 4096
ssl_certificate: /etc/ssl/certs/web1.pem

# Override any variable at runtime
ansible-playbook site.yml -e "http_port=8080"

# inventory/aws_ec2.yml
plugin: aws_ec2
regions:
  - eu-west-1
filters:
  tag:Environment:
    - production
  instance-state-name: running
keyed_groups:
  - key: tags.Role
    prefix: role
  - key: placement.availability_zone
    prefix: az
compose:
  ansible_host: private_ip_address

# List discovered hosts
ansible-inventory -i inventory/aws_ec2.yml --list

# Use in playbook
ansible-playbook -i inventory/aws_ec2.yml site.yml

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

def get_inventory():
    # Fetch from your CMDB, API, or database
    hosts = requests.get("https://cmdb.internal/api/hosts").json()

    inventory = {
        "webservers": {
            "hosts": [h["fqdn"] for h in hosts if h["role"] == "web"],
            "vars": {"http_port": 80}
        },
        "dbservers": {
            "hosts": [h["fqdn"] for h in hosts if h["role"] == "db"],
        },
        "_meta": {
            "hostvars": {
                h["fqdn"]: {"ansible_host": h["ip"]}
                for h in hosts
            }
        }
    }
    return inventory

if __name__ == "__main__":
    print(json.dumps(get_inventory(), indent=2))

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

# All hosts
ansible all -m ping

# Specific group
ansible webservers -m ping

# Multiple groups
ansible 'webservers:dbservers' -m ping

# Intersection (hosts in BOTH groups)
ansible 'webservers:&production' -m ping

# Exclusion
ansible 'all:!loadbalancers' -m ping

# Pattern matching
ansible 'web*.example.com' -m ping

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

# First host in group
ansible 'webservers[0]' -m ping

# Range
ansible 'webservers[0:2]' -m ping

inventory/
  production/
    hosts.yml
    group_vars/
      all.yml       # production-specific defaults
  staging/
    hosts.yml
    group_vars/
      all.yml       # staging-specific defaults
  development/
    hosts.yml
    group_vars/
      all.yml       # dev-specific defaults

ansible-playbook -i inventory/staging site.yml
ansible-playbook -i inventory/production site.yml

# List all hosts
ansible-inventory -i inventory/ --list

# Show specific host variables
ansible-inventory -i inventory/ --host web1.example.com

# Graph view
ansible-inventory -i inventory/ --graph

# Test connectivity
ansible all -i inventory/ -m ping