RE: Reflecting on docker build speed

I agree on all of the above. I tend to use custom --entrypoint="/bin/bash" for cases when I want to override defaults for debugging or exec -it for attaching to the already running container. Quite interesting feature of the volume mount, not described anywhere, is that with a fine grained target it can be maliciously used to workaround 30 day limit of most of the s/w trials. And about the tiered base images, people behind https://github.com/phusion/baseimage-docker did a really good job.