As part of the debugging work for Argus, Mesos added a new TTYInfo field to its ContainerInfo protobuf. This allows a container to optionally be launched with its STDIN, STDOUT, and STDERR redirected through a server side PTY device.
Setting this field triggers the creation of a new component in Mesos called an IOSwitchboard, which allows external clients to connect to the STDIN, STDOUT, and STDERR from a remote machine. This is extremely useful for debugging, as well as for attaching your local terminal to long running services that have been launched as Mesos tasks (e.g. a python interpreter or the SPARK shell).
Currently this feature is not exposed via metronome, so there is no way to take advantage of it in DC/OS.