> If you mean a scenario where Docker launches systemd, we don't do that. In my view Docker is just a packaging system; each container's pid 1 is the app we're deploying.

No, systemd is actually capable of running Docker containers directly (even without Docker).

I definitely wouldn't recommend running systemd inside a container unless you're using systemd to launch the container (instead of Docker), since Docker doesn't handle init systems very well, whereas systemd has this built-in. Though you can also go with the one-app-process-per-container approach as well with systemd, which also works.

If you have any citations that describe how to make systemd run Docker containers without Docker, I'd like to see them.

Starting with systemd 219, you can download a Docker image from a registry with "machinectl pull-dkr", and run it with "machinectl start":

http://www.freedesktop.org/software/systemd/man/machinectl.h...