We're running all the containers on Mesos hosts, so really all Ansible needs to do for us is talk to Marathon. We realized early on down this path that to accommodate scale we'd need to have some sort of scheduler. Mesos happened to be the most robust.

We originally tried the docker module in Ansible but found it had a few problems. There's been a lot of work on it since, and I expect it will be in a much better state when Ansible 2.0 is released.