I've not been impressed by docker outside of the local development experience (primarily, creating sandboxes and avoiding installing stuff on the main OS, and not having the latency of starting up a VM).

This discussion is about Kubernetes though. Docker is mostly only incidental to Kubernetes. It's a much better thought through system than anything I've seen come out of the Docker world. Docker images are adequate; Dockerfile as a build mechanism for images is deeply flawed, requiring so many kludges and duct tape to accommodate shared dependencies, rebuild on upstream change, shrinking after building, etc.

Hopefully a better system for building images to run on Kubernetes will crop up.