Vars plugins inject additional variable data into Ansible runs that did not come from an inventory source, playbook, or command line. Playbook constructs like ‘host_vars’ and ‘group_vars’ work using vars plugins.
Vars plugins were partially implented in Ansible 2.0 and rewritten to be fully implemented starting with Ansible 2.4.
The host_group_vars plugin shipped with Ansible enables reading variables from host_vars and group_vars.
You can activate a custom vars plugins by either dropping it into a
vars_plugins directory adjacent to your play, inside a role, or by putting it in one of the directory sources configured in ansible.cfg.
You can use
ansible-doc -t vars -l to see the list of available plugins.
ansible-doc -t vars <plugin name> to see specific plugin-specific documentation and examples.