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Inventory management

Chapter objectives​

  • Understand the role of the inventory
  • Create static inventories
  • Organize hosts into groups
  • Use dynamic inventories

1 - What is the inventory?​

Definition​

The inventory is the list of machines (hosts) that Ansible can manage.

Supported formats​

FormatExtensionUse
INI.iniSimple, readable
YAML.ymlStructured, powerful
DynamicScript/PluginCloud, CMDB

2 - INI inventory (basic)​

Basic syntax​

# inventory/hosts.ini

# Hôtes sans groupe (groupe implicite "ungrouped")
server1.example.com
192.168.1.10

# Groupe webservers
[webservers]
web-01 ansible_host=192.168.1.11
web-02 ansible_host=192.168.1.12
web-03 ansible_host=192.168.1.13

# Groupe databases
[databases]
db-01 ansible_host=192.168.1.20
db-02 ansible_host=192.168.1.21

# Groupe loadbalancers
[loadbalancers]
lb-01 ansible_host=192.168.1.5

Groups of groups (children)​

# inventory/hosts.ini

[webservers]
web-01
web-02

[databases]
db-01

[loadbalancers]
lb-01

# Groupe parent contenant d'autres groupes
[production:children]
webservers
databases
loadbalancers

# Autre exemple
[frontend:children]
webservers
loadbalancers

[backend:children]
databases

Variables in the inventory​

# Variables pour un hôte
[webservers]
web-01 ansible_host=192.168.1.11 http_port=80 max_clients=200
web-02 ansible_host=192.168.1.12 http_port=8080

# Variables pour un groupe
[webservers:vars]
nginx_version=1.24
document_root=/var/www/html
ansible_user=deploy

[databases:vars]
db_port=5432
backup_enabled=true

3 - YAML inventory​

YAML syntax​

# inventory/hosts.yml
all:
  children:
    webservers:
      hosts:
        web-01:
          ansible_host: 192.168.1.11
          http_port: 80
        web-02:
          ansible_host: 192.168.1.12
          http_port: 8080
      vars:
        nginx_version: "1.24"
        document_root: /var/www/html
    
    databases:
      hosts:
        db-01:
          ansible_host: 192.168.1.20
        db-02:
          ansible_host: 192.168.1.21
      vars:
        db_port: 5432
    
    production:
      children:
        webservers:
        databases:

INI vs YAML comparison​

4 - Host patterns​

Target hosts​

# Tous les hôtes
ansible all -m ping

# Un groupe spécifique
ansible webservers -m ping

# Un hôte spécifique
ansible web-01 -m ping

# Plusieurs groupes (OR)
ansible 'webservers:databases' -m ping

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

# Exclusion
ansible 'webservers:!web-03' -m ping

# Pattern avec wildcard
ansible 'web-*' -m ping

# Par numéro (range)
ansible 'web-[01:03]' -m ping

Pattern examples​

5 - Inventory variables​

Variable hierarchy​

group_vars and host_vars files​

inventory/
├── hosts.ini
├── group_vars/
│   ├── all.yml           # Variables pour tous
│   ├── webservers.yml    # Variables groupe webservers
│   └── databases.yml     # Variables groupe databases
└── host_vars/
    ├── web-01.yml        # Variables spécifiques web-01
    └── db-01.yml         # Variables spécifiques db-01
# group_vars/all.yml
---
ansible_user: deploy
timezone: Europe/Paris
ntp_servers:
  - ntp1.example.com
  - ntp2.example.com
# group_vars/webservers.yml
---
nginx_version: "1.24"
nginx_worker_processes: auto
nginx_worker_connections: 1024
# host_vars/web-01.yml
---
nginx_worker_processes: 4
backup_enabled: true

6 - Connection variables​

Built-in Ansible variables​

# Connexion SSH
ansible_host: 192.168.1.10        # IP ou hostname
ansible_port: 22                   # Port SSH
ansible_user: deploy               # Utilisateur distant
ansible_ssh_private_key_file: ~/.ssh/deploy_key

# Escalade de privilèges
ansible_become: true               # Activer sudo
ansible_become_method: sudo        # Méthode (sudo, su, doas)
ansible_become_user: root          # Utilisateur cible
ansible_become_password: secret    # Mot de passe sudo

# Python
ansible_python_interpreter: /usr/bin/python3

# Type de connexion
ansible_connection: ssh            # ssh, local, docker, winrm

Complete example​

# inventory/hosts.ini
[webservers]
web-01 ansible_host=192.168.1.11 ansible_user=ubuntu ansible_ssh_private_key_file=~/.ssh/aws.pem
web-02 ansible_host=192.168.1.12 ansible_user=ubuntu

[databases]
db-01 ansible_host=192.168.1.20 ansible_user=postgres ansible_become_password=dbadmin

[windows]
win-01 ansible_host=192.168.1.30 ansible_connection=winrm ansible_user=Administrator ansible_password=P@ssw0rd

[local]
localhost ansible_connection=local

7 - Dynamic inventories​

Concept​

AWS EC2​

# inventory/aws_ec2.yml
plugin: amazon.aws.aws_ec2
regions:
  - eu-west-1
  - eu-central-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: public_ip_address
# Installer la collection
ansible-galaxy collection install amazon.aws

# Lister les hôtes
ansible-inventory -i inventory/aws_ec2.yml --list

# Utiliser
ansible all -i inventory/aws_ec2.yml -m ping

Custom script​

#!/usr/bin/env python3
# inventory/dynamic.py

import json
import argparse

def get_inventory():
    return {
        "webservers": {
            "hosts": ["web-01", "web-02"],
            "vars": {
                "http_port": 80
            }
        },
        "databases": {
            "hosts": ["db-01"]
        },
        "_meta": {
            "hostvars": {
                "web-01": {"ansible_host": "192.168.1.11"},
                "web-02": {"ansible_host": "192.168.1.12"},
                "db-01": {"ansible_host": "192.168.1.20"}
            }
        }
    }

if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('--list', action='store_true')
    parser.add_argument('--host', action='store')
    args = parser.parse_args()
    
    if args.list:
        print(json.dumps(get_inventory()))
    elif args.host:
        print(json.dumps({}))
# Rendre exécutable
chmod +x inventory/dynamic.py

# Tester
./inventory/dynamic.py --list

# Utiliser
ansible all -i inventory/dynamic.py -m ping

8 - Multi-environment​

inventory/
├── production/
│   ├── hosts.ini
│   ├── group_vars/
│   │   ├── all.yml
│   │   └── webservers.yml
│   └── host_vars/
│       └── web-01.yml
├── staging/
│   ├── hosts.ini
│   └── group_vars/
│       └── all.yml
└── development/
    ├── hosts.ini
    └── group_vars/
        └── all.yml

Usage​

# Déploiement production
ansible-playbook -i inventory/production/ site.yml

# Déploiement staging
ansible-playbook -i inventory/staging/ site.yml

# Déploiement dev
ansible-playbook -i inventory/development/ site.yml

9 - Useful commands​

Inspect the inventory​

# Lister tous les hôtes
ansible-inventory --list

# Format graphique
ansible-inventory --graph

# Afficher les variables d'un hôte
ansible-inventory --host web-01

# Valider la syntaxe
ansible-inventory -i inventory/ --list

Example of --graph output​

@all:
  |--@production:
  |  |--@webservers:
  |  |  |--web-01
  |  |  |--web-02
  |  |--@databases:
  |  |  |--db-01
  |--@ungrouped:

Summary​

Key points
  • The inventory defines YOUR target hosts
  • Organize with hierarchical groups
  • Separate variables into group_vars/host_vars
  • Use dynamic inventories for the cloud

Practical exercises​

  1. Create an inventory with 3 groups: web, db, cache
  2. Add group and host variables
  3. Test the selection patterns
  4. Create a multi-environment inventory

← Installation | Ad-hoc commands →