I want to install python packages within docker containers. Since the build of some packages is time-consuming and sometimes fails, I want to use a cache that is reused.
I found the mount type cache in the docker documentation and this question Using a pip cache directory in docker builds
But pip always downloads the package without using the cache. Moreover the cache is always empty when building again.
# syntax = docker/dockerfile:experimental
FROM python
RUN --mount=type=cache,target=/root/.cache/pip ls -la /root/.cache/pip
RUN --mount=type=cache,target=/root/.cache/pip pip cache list
RUN --mount=type=cache,target=/root/.cache/pip pip install tqdm
CMD python -c "print('Hello World')"
I build with the following command:
docker build -t test --progress=plain . --no-cache
How can I use the cache?
The underlying problem is that the pip packages, I use, need to be compiled from source by pip. I used —prefer-binary, but nevertheless some packages are not available as binary for my architecture (raspberry pi). The binary package building fails and I have to retry with some new dev dependencies that are missing. I want to use the compiled wheels from the cache for the packages that already succeeded.
