Just wrote something very similar, but more targeting development sandboxes. host runs a script that uses rubydns. a zone cut to the host for dev.domain.com. rubydns then uses docker-api (with small redis cache) to respond to dns requests for *.dev.domain.com. Developers can now reference their sandboxes as foo.dev.domain.com from within the host, or anywhere else, including their own machines. More to it then this ofcourse, but thats the dns portion.