Tightened up how the Docker containers are created.

.dockerignore

@@ -0,0 +1,7 @@
+*
+
+! setup.py
+! requirements*.txt
+! vasl_templates/
+! docker/
+! LICENSE.txt

Dockerfile

@@ -1,27 +1,39 @@
 # NOTE: Use the run-container.sh script to build and launch this container.
 
-FROM python:alpine3.6
+# We do a multi-stage build (requires Docker >= 17.05) to install everything, then copy it all
+# to the final target image.
 
+FROM python:alpine3.6 AS base
+
+# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+FROM base AS build
+
+# install the requirements
 # NOTE: pillow needs zlib and jpeg, lxml needs libxslt, we need build-base for gcc, etc.
 RUN apk add --no-cache build-base zlib-dev jpeg-dev libxslt-dev
-ENV LIBRARY_PATH=/lib:/usr/lib
-
-WORKDIR /app
 
+# install the application requirements
+COPY requirements.txt requirements-dev.txt ./
+RUN pip install -r requirements.txt
 ARG ENABLE_TESTS
+RUN if [ "$ENABLE_TESTS" ]; then pip install -r requirements-dev.txt ; fi
 
-# install the Python requirements
-COPY requirements.txt requirements-dev.txt ./
-RUN pip install -r requirements.txt ; \
-    if [ "$ENABLE_TESTS" ]; then pip install -r requirements-dev.txt ; fi
+# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+FROM base
+COPY --from=build /usr/local/lib/python3.6/site-packages /usr/local/lib/python3.6/site-packages
+RUN apk add --no-cache libjpeg
 
 # install the application
-ADD vasl_templates vasl_templates
-COPY setup.py LICENSE.txt ./
+WORKDIR /app
+COPY vasl_templates vasl_templates
+COPY setup.py requirements.txt requirements-dev.txt LICENSE.txt ./
 RUN pip install -e .
 
 # copy the config files
 COPY docker/config/* vasl_templates/webapp/config/
+ARG ENABLE_TESTS
 RUN if [ "$ENABLE_TESTS" ]; then echo "ENABLE_REMOTE_TEST_CONTROL = 1" >>vasl_templates/webapp/config/debug.cfg ; fi
 
 EXPOSE 5010