Ansible host inventories can include groups of host groups. This is accomplished by creating a host group name with the :children suffix. The following example creates a new group called north-america, which includes all hosts from the usa and canada groups.

[usa]
washington1.example.com
washington2.example.com

[canada]
ontario01.example.com
ontario02.example.com

[north-america:children]
canada
usa

A group can have both managed hosts and child groups as members. For example, in the previous inventory you could add a [north-america] section that has its own list of managed hosts. That list of hosts would be merged with the additional hosts that the north-america group inherits from its child groups.

You can specify ranges in the hostnames or IP addresses to simplify Ansible host inventories. You can specify either numeric or alphabetic ranges. Ranges have the following syntax:

[START:END]

Ranges match all values from START to END, inclusively. Consider the following examples:

If leading zeros are included in numeric ranges, they are used in the pattern. The second example above does not match server1.example.com but does match server07.example.com. To illustrate this, the following example uses ranges to simplify the [usa] and [canada] group definitions from the preceding example:

[usa]
washington[1:2].example.com

[canada]
ontario[01:02].example.com

When in doubt, use the ansible-navigator inventory command to verify a machine's presence in the inventory. In the following example, ansible-navigator inventory is run in stdout mode. The first query matches a host in the inventory, and the second does not.

[user@controlnode ~]$ ansible-navigator inventory -m stdout \
> --host washington1.example.com
{}
[user@controlnode ~]$ ansible-navigator inventory -m stdout \
> --host washington01.example.com
[WARNING]: Could not match supplied host pattern, ignoring: washington01.example.com
...output omitted...

The following command lists all hosts in the inventory.

[user@controlnode ~]$ ansible-navigator inventory -m stdout --list
{
    "_meta": {
        "hostvars": {}
    },
    "all": {
        "children": [
            "canada",
            "ungrouped",
            "usa"
        ]
    },
    "canada": {
        "hosts": [
            "ontario01.example.com",
            "ontario02.example.com"
        ]
    },
    "usa": {
        "hosts": [
            "washington1.example.com",
            "washington2.example.com"
        ]
    }
}

The following command lists all hosts in a group.

[user@controlnode ~]$ ansible-navigator inventory -m stdout --graph canada
@canada:
  |--ontario01.example.com
  |--ontario02.example.com

Run the ansible-navigator inventory command to interactively browse inventory hosts and groups:

[user@controlnode ~]$ ansible-navigator inventory
  Title             Description
0│Browse groups     Explore each inventory group and group members members
1│Browse hosts      Explore the inventory with a list of all hosts

Type :0 to select "Browse Groups":

  Name                                Taxonomy                         Type
0│canada                              all                              group
1│ungrouped                           all                              group
2│usa                                 all                              group

Press the ESC key to exit the Groups menu. Type :1 to select "Browse Hosts"

  Inventory hostname
0│ontario01.example.com
1│ontario02.example.com
2│washington1.example.com
3│washington2.example.com

Press the ESC key twice to exit ansible-navigator inventory.

The /etc/ansible/hosts file is considered the system's default static inventory file. However, normal practice is not to use that file but to specify a different location for your inventory files.

The ansible-navigator commands that you use to run playbooks can specify the location of an inventory file on the command line with the --inventory PATHNAME or -i PATHNAME option, where PATHNAME is the path to the desired inventory file.