multi-stage Docker build

backend/Dockerfile.multi

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+########
+# Python dependencies builder
+#
+# Full official Debian-based Python image
+FROM python:3-stretch AS builder
+
+# Always set a working directory
+WORKDIR /app
+# Sets utf-8 encoding for Python et al
+ENV LANG=C.UTF-8
+ENV PYTHONDONTWRITEBYTECODE=1
+ENV PYTHONUNBUFFERED=1
+
+
+# Ensures that the python and pip executables used
+# in the image will be those from our virtualenv.
+ENV PATH="/venv/bin:$PATH"
+
+# Install OS package dependencies.
+# Do all of this in one RUN to limit final image size.
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+        build-essential && \
+        rm -rf /var/lib/apt/lists/*
+
+# Setup the virtualenv
+RUN python -m venv /venv
+
+# Install Python deps
+COPY requirements.txt ./
+RUN pip install --no-cache-dir -r requirements.txt
+
+
+# Actual container
+#
+#
+FROM python:3-slim-stretch AS app
+
+# Extra python env
+ENV PATH="/venv/bin:$PATH"
+
+WORKDIR /app
+EXPOSE 8080
+
+# copy in Python environment
+COPY --from=builder /venv /venv
+
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+        libxml2 && \
+    rm -rf /var/lib/apt/lists/*
+
+# copy in the rest of the app
+COPY ./ ./
+ENTRYPOINT [ "python" ]
+CMD ["ghstats.py"]