Inventory is a list of servers that Ansible uses to manage the resources.

There are two different type of inventories:

Static

Manual inventory that we manage.

Dynamic

The inventory source is imported automatically from cloud providers as EC2, Azure, OpenStack, and more.

How to use the inventory file?

There are many ways to setup the inventory file on your controller machine.

Inventory file location

| level | path                 | note        |
| ----- | -------------------- | ----------- |
| root  | /etc/ansible/hosts   |             |
| user  | $USER/.ansible/hosts | recommended |

If you are using a different path, you must to specify the inventory file using the parameter -i.

Creating a basic inventory file

Ansible support many formats, below we gonna show three (INI,YAML and JSON).

For this example, we gonna create two groups with two hosts inside in each.

| group     | hosts                                                |
| --------- | ---------------------------------------------------- |
| webserver | test-web-001.mydomain.com, test-web-002.mydomain.com |
| database  | test-db-001.mydomain.com, test-db-002.mydomain.com   |

INI format

[webserver]
test-web-001.mydomain.com
test-web-002.mydomain.com
     
[database]
test-db-001.mydomain.com
test-db-002.mydomain.com

YAML format

---
all:
  children:
    webserver:
      hosts:
        test-web-001.mydomain.com:
        test-web-002.mydomain.com:
    database:
      hosts:
        test-db-001.mydomain.com:
        test-db-002.mydomain.com:

JSON format

{
    "all": {
        "children": {
            "webserver": {
                "hosts": {
                    "test-web-001.mydomain.com": null,
                    "test-web-002.mydomain.com": null
                }
            },
            "database": {
                "hosts": {
                    "test-db-001.mydomain.com": null,
                    "test-db-002.mydomain.com": null
                }
            }
        }
    }
}

Listing the Inventory

$ ansible-inventory --inventory-file=[inventory_file] --list

Listing the Inventory and filter by a specific host

$ ansible-inventory --inventory-file=[inventory_file] --host [hostname]