Inventory — Telling Ansible What to Manage

ansible1-2 used -i inventory in every command without explaining what that file actually was. This chapter delivers — the inventory is Ansible's own list of hosts, and how it's organized shapes everything else in this course.

What an Inventory Actually Is

A plain-text file listing the hosts Ansible can manage, optionally organized into named groups. Two common formats: INI-style — simple, classic — and YAML, more structured and consistent with every other Ansible file this course writes.

INI-Style Inventory

Bracketed headers define groups; hosts listed underneath belong to that group. The :vars suffix attaches variables to every host in that group at once — http_port here applies to both web1 and web2 without repeating it per host.

YAML-Style Inventory

The exact same inventory, expressed as YAML — more verbose for a trivial case like this one, but it scales far better once groups nest deeply or carry many variables, and it keeps every file in an Ansible project speaking the same syntax.

Groups of Groups — Nested Groups

A group can itself be composed of other groups. production here contains every host in both webservers and dbservers — a play targeting hosts: production reaches all of them at once, without listing each individual group.

Host Variables and Group Variables

Inline :vars works, but group_vars/ and host_vars/ directories are the cleaner, more common approach at any real scale — one YAML file per host or group, automatically loaded by Ansible based on the filename matching the group or host name exactly:

No explicit reference to these files is needed anywhere — Ansible loads group_vars/webservers.yml automatically for any host in the webservers group, purely by matching the filename.

Special Built-In Groups

• all — every host in the inventory, always implicitly available, no matter how groups are defined
• ungrouped — any host not explicitly placed into a named group

Hands-On Exercises