Sure, docker-compose is great, but could we get similar functionality using just the tools that are built into CoreOS? Can we get automatic updates, too? Yes we can! 📦
Dependencies within unrelated projects (ie, sharing a single database container for a few unrelated apps) is something that would be pretty handy, and is missing from compose.
Auto-updates are cool - but also dangerous... I think there's something in running watchtower manually like I have been - when something breaks straight after, I know the cause.
I don't really understand what you're suggesting. Having a seperate compose file for your database would "work", but you'd lack any of the dependency handling.