We use phusion baseimage, which does have an init system (runit). We have been happy with that. Our customers are not ready for us to provide our product as 6 distinct linked docker containers. The image we build is more like a VM in that it contains multiple processes (pg, nginx, and some apps/services).
If you're providing an all-in-one solution like that, it sounds like you would be better served by just providing an OVF image to them.
Or better yet, keep 6 distinct containers like you should, and use docker-compose to spin them up together. Makes upgrades easier because you can simply point to a newer version of whatever service containers you're using without having to take out everything.
If you're using containers as a VM, you're essentially adding overhead for no good reason.
I am not sure if I saw it HN recently, but there is an article by Phusion [1] talking about the init process and how to handle it with Docker. They have a base image, baseimage-docker [2], that is supposed to solve that problem.
I remember reading centos tried to make systemd available in docker containers briefly but went back on it due to bugs (not sure if they were ever resolved). I've seen containers that need init management using supervisord.
