Further reduce the size of the docker image

[richvdh]

• get rid of the pip wheel cache
• get rid of /synapse (everything we need ends up in /usr/local/lib/python2.7/site-packages

[richvdh]

This is all very well, but we end up with an image which is built on top of a layer which adds /synapse, and then we remove /synapse in the final layer. Is there a way to avoid the redundant layer?

[michaelkaye]

You can do it with the builder container pattern : https://docs.docker.com/develop/develop-images/multistage-build/

That way you build synapse then throw away the container(s) you built it in and just copy the required bits into a new container - it makes it a little easier than having that one multi-line RUN command to try to make a single image.

[michaelkaye]

So - we can deploy this for a slight gain, if we remove the "rm -rf /synapse" as that's not doing anything useful to the size

Doing it properly will be about using the multi-stage builder to:

FROM python-alpine...
RUN apk install runtime_deps 
RUN apk install build_deps # seperate layers, because we can re-use the layer with just the runtime deps below, speeding up builds I think.

pip install to /target/ # somehow, how do you do that in python
other bits here

FROM python-alpine
RUN apk install runtime_deps # this is ok as a separate layer
COPY --from = 0 /target

Then i think we get to re-use layers where we want them - runtime dependencies, and build dependencies, without affecting the end image size.

[michaelkaye]

If we remove this line then this will reduce the size a little without doing deletes that aren't worthwhile.

[richvdh]

well, in for a penny, in for a pound. A semi-interesting exercise in learning how dockerfiles work.