Making docs image 40% smaller and also making python version upgrades easier for multi-stage builds. (#2836)

Co-authored-by: Bruno Alla <alla.brunoo@gmail.com>

{{cookiecutter.project_slug}}/compose/local/docs/Dockerfile

@@ -1,28 +1,57 @@
-FROM python:3.9-slim-bullseye
+ARG PYTHON_VERSION=3.9-slim-bullseye
+
+# define an alias for the specfic python version used in this file.
+FROM python:${PYTHON_VERSION} as python
+
+
+# Python build stage
+FROM python as python-build-stage
 
-ENV PYTHONUNBUFFERED 1
 ENV PYTHONDONTWRITEBYTECODE 1
 
-RUN apt-get update \
+RUN apt-get update && apt-get install --no-install-recommends -y \
   # dependencies for building Python packages
-    && apt-get install -y build-essential \
+  build-essential \
   # psycopg2 dependencies
-    && apt-get install -y libpq-dev \
-    # Translations dependencies
-    && apt-get install -y gettext \
-    # Uncomment below lines to enable Sphinx output to latex and pdf
-    # && apt-get install -y texlive-latex-recommended \
-    # && apt-get install -y texlive-fonts-recommended \
-    # && apt-get install -y texlive-latex-extra \
-    # && apt-get install -y latexmk \
+  libpq-dev \
   # cleaning up unused files
   && apt-get purge -y --auto-remove -o APT::AutoRemove::RecommendsImportant=false \
   && rm -rf /var/lib/apt/lists/*
 
 # Requirements are installed here to ensure they will be cached.
 COPY ./requirements /requirements
-# All imports needed for autodoc.
-RUN pip install -r /requirements/local.txt -r /requirements/production.txt
+
+# create python dependency wheels
+RUN pip wheel --no-cache-dir --no-deps --wheel-dir /usr/src/app/wheels  \
+  -r /requirements/local.txt -r /requirements/production.txt \
+  && rm -rf /requirements
+
+
+# Python 'run' stage
+FROM python as python-run-stage
+
+ARG BUILD_ENVIRONMENT
+ENV PYTHONUNBUFFERED 1
+ENV PYTHONDONTWRITEBYTECODE 1
+
+RUN apt-get update && apt-get install --no-install-recommends -y \
+  # Translations dependencies
+  gettext \
+  # Uncomment below lines to enable Sphinx output to latex and pdf
+  # texlive-latex-recommended \
+  # texlive-fonts-recommended \
+  # texlive-latex-extra \
+  # latexmk \
+  # cleaning up unused files
+  && apt-get purge -y --auto-remove -o APT::AutoRemove::RecommendsImportant=false \
+  && rm -rf /var/lib/apt/lists/*
+
+# copy python dependency wheels from python-build-stage
+COPY --from=python-build-stage /usr/src/app/wheels /wheels
+
+# use wheels to install python dependencies
+RUN pip install --no-cache /wheels/* \
+  && rm -rf /wheels
 
 COPY ./compose/local/docs/start /start-docs
 RUN sed -i 's/\r$//g' /start-docs