I really love Docker, but I think there a few areas where I'm not a fan. For one, if I'm using Docker on a production machine, I make sure that machine is only for Docker containers. There have been a bunch of ways to escalate privileges to the broader machine, so it doesn't seem (to me) to be a great idea to run Docker alongside other more traditionally deployed apps on the same machine. Part of that is philosophical though and I think the use cases where Docker shines dictate that it owns the box.

Many people aren't ready to further abstract away from bare metal by adding a container layer for process management on top of the operating system which may be running inside a hypervisor. And there are situations where that's problematic. So it's not a great fit there either.