I'm not quite sure, if this is actually needed for resolving hostnames in the config. If everything works without the resolver config option, then lets just remove it.
I would just get rid of all the commented out options, if we don't use them anyway (and instead maybe link to a full-fledged config example from the docs or something).
I would rather remove this check and have it just fail while running the Ansible playbook, rather than installing a broken Kea deployment.
Thanks for the changes, looks good! Just two notes.
This should probably use dooris__hostname.
Having those be hardcoded with all else being configurable is a bit awkward, so I think making these variables as well make sense.
Let's have a comment here to note that we leave this name for backwards compatibility.