[atemerev]

Supervisord is the officially blessed solution:

https://docs.docker.com/engine/admin/using_supervisord/

[masklinn]

supervisord specifically documents that it's not an init and shouldn't be used as an init, that's the second paragraph of its home page: http://supervisord.org/index.html?highlight=init

[DannoHung]

That is literally not at all what that is suggesting.