Comment by antoniomika

I actually developed a system similar to this but used docker compose as an alternative to Procfiles and nginx+le to handle dynamic virtual hosting. It's actually a golang app that will automatically provision git repos with the necessary hooks and also allow you to exec into a container directly over SSH. I had the thought of using docker stack to achieve zero downtime but haven't had a chance to try that out. Happy to open source it if anyone is interested in using it.