02-inventory.md

Inventory

Ansible inventory file is a fundamental component of Ansible that defines the hosts (remote systems) that you want to manage and the groups those hosts belong to. The inventory file can be static (a simple text file) or dynamic (generated by a script). It provides Ansible with the information about the remote nodes to communicate with during its operations.

Static Inventory

A static inventory file is typically a plain text file (usually named hosts or inventory) and is structured in INI or YAML format. Here are examples of both formats:

INI Format

# inventory file: hosts

[webservers]
web1.example.com
web2.example.com

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

[all:vars]
ansible_user=admin
ansible_ssh_private_key_file=/path/to/key

YAML

# inventory file: hosts.yaml

all:
  vars:
    ansible_user: admin
    ansible_ssh_private_key_file: /path/to/key
  children:
    webservers:
      hosts:
        web1.example.com:
        web2.example.com:
    dbservers:
      hosts:
        db1.example.com:
        db2.example.com:

Dynamic Inventory

A dynamic inventory is generated by a script or plugin and can be used for environments where hosts are constantly changing (e.g., cloud environments). The script or plugin fetches the list of hosts from a source like AWS, GCP, or any other dynamic source.

Here is an example of a dynamic inventory script for AWS EC2:

#!/usr/bin/env python

import json
import boto3

def get_aws_ec2_inventory():
    ec2 = boto3.client('ec2')
    instances = ec2.describe_instances()
    inventory = {
        'all': {
            'hosts': [],
            'vars': {
                'ansible_user': 'ec2-user',
                'ansible_ssh_private_key_file': '/path/to/key'
            }
        },
        '_meta': {
            'hostvars': {}
        }
    }

    for reservation in instances['Reservations']:
        for instance in reservation['Instances']:
            if instance['State']['Name'] == 'running':
                public_ip = instance['PublicIpAddress']
                inventory['all']['hosts'].append(public_ip)
                inventory['_meta']['hostvars'][public_ip] = {
                    'ansible_host': public_ip
                }

    print(json.dumps(inventory, indent=2))

if __name__ == '__main__':
    get_aws_ec2_inventory()

Usage

ansible-playbook -i inventory <Adhoc command or Playbook.yml>