[davexunit]

>making reproducible builds.

Docker builds actually aren't reproducible. There are many sources of non-determinism that Docker cannot address. Do you use the base images from DockerHub as-is or do you run 'apt-get upgrade' or whatever for security patches? If you do, the result you get from building that image (as opposed to using what's in a cache) is different depending on the time it was built. The same goes for any Dockerfiles that compile from source. Hell, just extracting a source tarball results in a different hash of the source tree because of the timestamps on the files. You and I have little hope of building the same image and getting the same exact result.

Build reproducibility is a very interesting topic with some unsolved issues, but Docker isn't helping with it. See https://reproducible.debian.net for a good resource about build reproducibility.

[vezzy-fnord]

Don't know why you were downvoted. Docker doesn't give you reproducible builds because you're still running in a raw host OS environment with all its state, but simply the subsystems partitioned into their own namespaces. Docker is more akin to a snapshot than reproducible.