I'd like to point out that a docker container, usually doesn't run an init system. [I get that OP was talking about standalone alpine]
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.
[1]: https://blog.phusion.nl/2015/01/20/docker-and-the-pid-1-zomb... [2]: https://phusion.github.io/baseimage-docker/