The problem I have with traditional configuration management is that in the end, even if it's declerative, you are stil modifying a imperative OS/userland. So it will collect state at some point. Things like undoing changes with those tools is not that trivial. You have to actively reverse them in your configuration. Which turns nice CM code into mess. Want to try out something quick? Better not be afraid it messes up your OS/userland as there is no simple undo.

So since I'm doing isolation in containers/Docker already it's a small step to a lightweight Kubernetes. What Kubernetes gives me on top of that is that I can consider everything below the application layer as a declarative API.