backend: avoid redundant steps in Dockerfile

Use separate `base`, `setup` and `final` to avoid redundat steps.
Avoid runnig `poetry` twice, and add `source` and `description`.

Signed-off-by: Jakub Sokołowski <jakub@status.im>

spiffworkflow-backend/Dockerfile

@@ -1,28 +1,35 @@
-FROM ghcr.io/sartography/python:3.11
+# Base image to share ENV vars that activate VENV.
+FROM ghcr.io/sartography/python:3.11 AS base
+
+ENV VIRTUAL_ENV=/app/venv
+RUN python3 -m venv $VIRTUAL_ENV
+ENV PATH="$VIRTUAL_ENV/bin:$PATH"
+
+WORKDIR /app
+
+# Setup image for installing Python dependencies.
+FROM base AS setup
 
 RUN pip install poetry
 RUN useradd _gunicorn --no-create-home --user-group
 
-RUN apt-get update && \
-    apt-get install -y -q \
-        gcc libssl-dev \
-        curl git-core libpq-dev \
-        gunicorn3 default-mysql-client
+RUN apt-get update \
+ && apt-get install -y -q gcc libssl-dev libpq-dev
 
-WORKDIR /app
-COPY pyproject.toml poetry.lock /app/
+COPY . /app
 RUN poetry install --without dev
 
-RUN set -xe \
-  && apt-get remove -y gcc python3-dev libssl-dev \
-  && apt-get autoremove -y \
-  && apt-get clean -y \
-  && rm -rf /var/lib/apt/lists/*
+# Final image without setup dependencies.
+FROM base AS final
 
-COPY . /app/
+LABEL source="https://github.com/sartography/spiff-arena"
+LABEL description="Software development platform for building, running, and monitoring executable diagrams"
 
-# run poetry install again AFTER copying the app into the image
-# otherwise it does not know what the main app module is
-RUN poetry install --without dev
+RUN apt-get update \
+ && apt-get clean -y \
+ && apt-get install -y -q curl git-core gunicorn3 default-mysql-client \
+ && rm -rf /var/lib/apt/lists/*
 
-CMD ./bin/boot_server_in_docker
+COPY --from=setup /app /app
+
+ENTRYPOINT ["./bin/boot_server_in_docker"]