Optimize master dockerfile

[nyurik]

The current 12-master/Dockerfile uses a single stage build, and tries to clean up at the end. I think it can be made significantly smaller by using a 2-stage build:

• the current code would be the first stage (cleanup can be removed)
• the second stage would just copy the build binaries from the first stage

This should (in theory) make the resulting image smaller. The biggest issue is knowing how to copy results -- I suspect it is usually the package maintainers who track those dependencies.

cc: @smellman

[ImreSamu]

@nyurik:
in theory it is a good idea, but when I checked the best practice in the upstream repo .. I realized that : the "multi-stage" builds is "heavily discouraged in official-images" see https://github.com/docker-library/postgres/issues/655#issuecomment-566815226 ( search "stage" ) and see https://github.com/docker-library/faq/#multi-stage-builds

[nyurik]

@ImreSamu thanks, I wasn't aware of the caching issue. I guess this is more of the build infrastructure shortcoming that should be solved on the server-side -- because otherwise you sacrifice bandwidth for the gain in build-time, but I do understand the concern.

That said, I think my proposal fits the 2nd case described in guidelines (if I understood it correctly):

two-stage build where the necessary artifact does not exist and must be built from source and/or the build process is going to be similarly highly deterministic (thus mitigating the cache concern somewhat)

[smellman]

I try to write multistage build on master branch.