Slim Python Dockerfile not executing

Question

I created a slim docker file for my app:

FROM python:3.7-slim-stretch AS build
RUN python3 -m venv /venv

RUN apt-get update && \
    apt-get upgrade -y && \
    apt-get install -y git && \
    apt-get install -y build-essential && \
    rm -rf /var/cache/apt/* /var/lib/apt/lists/*

ADD ./requirements.txt /project/
RUN /venv/bin/pip install -r /project/requirements.txt

ADD . /project
RUN /venv/bin/pip install /project
WORKDIR /project

FROM python:3.7-slim-stretch AS production
COPY --from=build /venv /venv
CMD ["/venv/bin/python3","-m", "myapp"]

The docker is building and working. The running python executable is copied from the build image. (Verified, if I remove "/venv/bin" it won't run). However, to save some space I want to change my production base docker to:

FROM debian:stretch-slim

But then I'm getting an error:

docker: Error response from daemon: OCI runtime create failed: container_linux.go:345: starting container process caused "exec: \"/venv/bin/python3\": stat /venv/bin/python3: no such file or directory": unknown.

Now, I don't understand this error. I can see the python executable is there, why he wouldn't run? Whats in the base python docker image allow it to run?

Answer 1

Go in your venv in your container and ls -l the bin directory.

lrwxrwxrwx 1 root root 21 Dec 4 17:28 python -> /usr/local/bin/python

Yes python is there but it is a symlink to a file which does not exists.

You can go around this first problem by using RUN python3 -m venv --copies /venv in your Dockerfile.

But you will then hit the following error message:

error while loading shared libraries: libpython3.7m.so.1.0: cannot open shared object file: No such file or directory

So you will finally need to install the exact same version of python in your image as the one available at build time.