Matthew Wild c1cf6ab1e5 Dockerfile: Split build into multiple stages ...

Currently the Dockerfile has a single RUN directive with all the needed
commands in it. This optimizes for image size by not creating too many
"layers" (which are only additive). However it means the result that gets
cached can basically never be reused, because any change to the source code
will need to execute the whole RUN block again.

This commit switches to a docker "multi-stage" build, where we have a build
image that is separate from the final one that gets published. The build
image can be cached locally, and size is no longer a significant concern.

This approach allows the single RUN command to be split up into multiple RUN
commands that only execute when strictly needed (i.e. when their result
is not cached locally).

This drastically improves the build time when rebuilding the image after
a simple code change, because the build image doesn't have to install all
the apt packages, for example. This leads to a nicer developer experience
when using docker locally for development and testing.

2022-01-08 13:17:52 +01:00

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