There's a few projects out now that do most of this for you; there's a lot of rapid innovation in higher-level docker tools.
eg https://github.com/remind101/empire (built ontop of EC2/ECS)
You get a 12 factor compatible PaaS out of it, pretty easy.
it is?
its one more step up the chain towards the ultimate goal: being able to run M isolated instances of N different apps automatically distributed across Y physical hosts (and being able to deploy app A without caring about any of this)
We're almost there.
