Deeper Dive into Inventories

After Getting Started, the first major topic is inventory design.

Within your inventory, you configure your devices. This may look intimidating at first, but it is fairly easy to understand once you break it down.

ini vs YAML

You can create an inventory file via either ini or YAML.

ini is easier to read and understand at first, while YAML is usually the better choice for larger networks with more diverse devices and roles.

inventory.ini Example

[routers]
200.0.0.3
200.0.0.2

[switches]
100.0.0.1
100.0.0.2

[routers:vars]
ansible_user=admin
ansible_password=<your_password>
ansible_connection=network_cli
ansible_network_os=cisco.ios.ios
ansible_become=yes
ansible_become_method=enable
ansible_become_password=<your_enable_password>

What Each Part Means

• [] defines a group. In this example, routers has two IP addresses.
• [routers:vars] means this group has variables tied to it.
• ansible_user and ansible_password are used for login over SSH.
• ansible_connection=network_cli indicates this is a network device workflow.
• ansible_network_os specifies the OS being automated.
• ansible_become, ansible_become_method, and ansible_become_password are for entering privileged mode (enable) when required.

Group Naming: The 3 W’s

As Ansible recommends, group names are clearer when they communicate:

• What: device role (leaf, spine, router)
• Where: location (ISL, USA, DC1)
• When: environment (dev, prod)

Example group: usa_leafs_dev.

YAML Metagroups Example

all:
  children:
    israel_dc:
      children:
        spines:
          hosts:
            spine01:
              ansible_host: 10.1.1.1
            spine02:
              ansible_host: 10.1.1.2
        leafs:
          hosts:
            leaf01:
              ansible_host: 10.1.2.1
            leaf02:
              ansible_host: 10.1.2.2
        ai_servers:
          hosts:
            ai-gpu01:
              ansible_host: 10.1.10.1
            ai-gpu02:
              ansible_host: 10.1.10.2
          vars:
            ansible_user: admin
            ansible_password: <your_password>
            ansible_port: 22

Add Variables to a Specific Group

When using metagroups in YAML, you can separate device roles and locations more clearly, then attach variables at the right level.

ai_servers:
  hosts:
    ai-gpu01:
      ansible_host: 10.1.10.1
    ai-gpu02:
      ansible_host: 10.1.10.2
  vars:
    ansible_user: admin
    ansible_password: <your_password>
    ansible_port: 22

Verify Inventory

The last part of inventory work is verification, meaning you confirm it is functional, reachable, and variables are correct.

ansible-inventory -i inventory.ini --list
ansible ai_servers -m ping -i inventory.ini

Where ai_servers can be replaced by another group, host, or all.

Example success output:

200.0.0.3 | SUCCESS => {
    "changed": false,
    "ping": "pong"
}

group_vars and host_vars

As your inventory grows, move variables into group_vars and host_vars so inventory files stay readable and reusable.