In case you missed it, Docker 17.05+ now supports multi-stage builds, which makes building minimal Elixir releases really easy.
Having worked out how to do this before multi-stage builds, using VOLUME mounts, multiple Dockerfiles, custom mix tasks and shell scripts, I can tell you, this is amazing easier: now all you need is Distillery, a base Elixir build image and docker build.
For guidance, please pop over to https://github.com/Financial-Times/docker-elixir-build and consult the README.
