What would you like to be added:

A backend for docker, similar with the kubernetes backend, that will read and also track any changes to containers and would use container labels to publish DNS records for said container.

Why is this needed:

Good question. CoreDNS is fast becoming (if it's not already) one of the most used DNS servers/forwarders, especially for simple lab setups. I would greatly improve it's use and adoption to have such a feature.