As originally reported by Tobias Müller in https://github.com/mesosphere/marathon/issues/2682#issuecomment-158356167
and in particular in https://github.com/mesosphere/marathon/issues/2682#issuecomment-158905946 :
> I never configured the WebUI URL manually before, even in 0.13.0-RC1. I'd rather guess that Marathon should be able to extract this from the Zookeeper connection string (respectively by retrieving the Master info from Zookeeper by the URL specified). The only thing I changed when going from RC1 to RC4 was changing the Docker image tag for the systemd service definition.
> The Mesos Master state.json URIs should be clear if Marathon knows which is the leading Master IMHO, or do I have a misunderstanding?