Dockerfile run apk add --virtual, build base, pip install

 https://stackoverflow.com/questions/46221063/what-is-build-deps-for-apk-add-virtual-command

apk installs global stuff into the container like python, dependecy packages,

pip install python sepcific libraries specified in requirement file

https://stackoverflow.com/questions/46221063/what-is-build-deps-for-apk-add-virtual-command

What is .build-deps for apk add --virtual command?

RUN apk add --no-cache --virtual .build-deps \
gcc \
freetype-dev \
musl-dev

RUN pip install --no-cache-dir <packages_that_require_gcc...> \

RUN apk del .build-deps

-t, --virtual NAME    Instead of adding all the packages to 'world', create a new 
                      virtual package with the listed dependencies and add that 
                      to 'world'; the actions of the command are easily reverted 
                      by deleting the virtual package

https://forums.docker.com/t/what-does-run-apk-add-do/128234

apk is Alpine Linux package system, so what it does is that it installs python, g++ and make

https://hub.docker.com/r/alpinelinux/build-base

Build base
This is a docker image that can be used to build Alpine Linux packages with abuild


DockerFile
From python:3.10-alpine3.14

RUN apk update
# gcc pytho3-dev musl-dev is for mysql client depedencies
RUN apk add --virtual build-deps gcc python3-dev musl-dev
RUN apk add --no-cache mariadb-dev

# For xmlsec required for  python3-saml
# https://pypi.org/project/xmlsec/
RUN apk add build-base libressl libffi-dev libressl-dev libxslt-dev libxml2-dev xmlsec-dev xmlsec

ENV PYTHONBUFFERED 1

COPY ./requirements.txt /requirements.txt

RUN pip install -r /requirements.txt

#
RUN apk add expat-dev
RUN pip install mod_wsgi-standalone

RUN apk del build-deps

RUN mkdir /app
WORKDIR /app
COPY ./app /app


requirements.txt
Django>=4.0.4,<4.1.0
djangorestframework>=3.13.1,<3.20.0

mysqlclient>=2.1.0,<2.2.0

flake8>=4.0.1,<4.1.0

lxml==4.9.3
xmlsec==1.3.13
python3-saml==1.11.0

requests>=2.28.1,<2.29.0

django-cors-headers >=3.13.0,<3.14.0

django-smtp-ssl>=1.0,<2.0