多阶段 dockerfile：如何在没有 --user pip3 参数的情况下安装？

Question

I'm new to docker, and I'm not entirely sure why this works.

I tried writing my dockerfile without the --user argument supplied to pip3 to install my requirements.txt file, but for some reason, copying the setup outputs from the ${INSTALL} dir to the ${APP} dir isn't working for me.

How can I write this such that I don't need to rely on the --user argument supplied to pip3 ?

Using said argument works for now, but it's just really bugging me that I can't make this do what I want it to do.

I build the image using this command:

docker image build --no-cache -t apptest .

Dockerfile

FROM python:3.8-alpine as base
ENV APP="/app"
ENV INSTALL="/install"
ENV LOC="/root/.local"
ENV LOCBIN="${LOC}/bin"
ENV PATH $PATH:${LOC}:${LOCBIN}

FROM base as builder
WORKDIR ${INSTALL}

COPY ./requirements.txt requirements.txt

#install all dependencies
RUN apk add --no-cache curl python3 pkgconfig python3-dev openssl-dev libffi-dev musl-dev make gcc
RUN pip3 install --user --no-cache-dir -r requirements.txt

FROM base

COPY --from=builder ${LOC} ${LOC}
COPY --from=builder ${LOCBIN} ${LOCBIN}
COPY ./src/ ${APP}
COPY ./src/Cogs/ ${APP}/Cogs
COPY ./src/Documentation/ ${APP}/Documentation
COPY ./src/Models/ ${APP}/Models
COPY ./src/OneNight/ ${APP}/OneNight

WORKDIR ${APP}

#start the service
ENTRYPOINT [ "python3", "service.py" ]

Answer 1

1. When you install Python packages, code goes all over the place. Eg libraries go into site-packages, scripts go into bin/, etc.. So you need to install everything in one place to make it easy to copy. Your options are --user or a virtualenv, basically, or copying lots of different directories. See https://pythonspeed.com/articles/multi-stage-docker-python/

2. That being said, you might not need a multi-stage build. You want one here because you're using a compiler. But you might only need a compiler because you're using Alpine Linux. For normal Linux distributions, most Python packages have binary precompiled wheels on PyPI, so much of the time you don't need a compiler at all.

It's quite possible switching to Debian-based base image ( python:3.8-slim-buster ) might allow you to just install everything without compiler. See https://pythonspeed.com/articles/alpine-docker-python/