Optimise the Docker file to minimise the number of layers and maximise the chances that changes will be in the last layers built.

pkg/docker/Dockerfile

@@ -22,13 +22,12 @@ RUN yarn install --cache-folder ./ycache --verbose && \
 FROM python:3.7-alpine3.9 as docs-builder
 
 # Install only dependencies absolutely required for documentation building
-RUN apk add --no-cache make
+RUN apk add --no-cache make && \
-RUN pip install --no-cache-dir \
+    pip install --no-cache-dir sphinx flask_security flask_paranoid python-dateutil flask_sqlalchemy flask_gravatar flask_migrate simplejson
-    sphinx flask_security flask_paranoid python-dateutil flask_sqlalchemy \
-    flask_gravatar flask_migrate simplejson
 
 COPY ./pgadmin4/ /pgadmin4
 
+# Build the docs
 RUN LC_ALL=en_US.UTF-8 LANG=en_US.UTF-8 make -C /pgadmin4/docs/en_US -f Makefile.sphinx html
 
 # Get the PG binaries
@@ -41,37 +40,6 @@ FROM postgres:11-alpine as pg11-builder
 # Then install backend, copy static files and set up entrypoint
 FROM python:3.7-alpine3.9
 
-RUN pip --no-cache-dir install gunicorn
-RUN apk add --no-cache postfix postgresql-client postgresql-libs
-
-WORKDIR /pgadmin4
-ENV PYTHONPATH=/pgadmin4
-
-# Install build-dependencies, build & install C extensions and purge deps in one RUN step
-# so that deps do not increase the size of resulting image by remaining in layers
-# NOTE: We're using PIP version 18.1 here because of this issue:
-#       https://github.com/pypa/pip/issues/6197
-COPY ./pgadmin4/requirements.txt /pgadmin4
-RUN set -ex && \
-    apk add --no-cache --virtual build-deps build-base postgresql-dev libffi-dev linux-headers && \
-    pip install --upgrade pip==18.1 && \
-    pip install --no-cache-dir -r requirements.txt && \
-    apk del --no-cache build-deps
-
-COPY --from=node-builder /pgadmin4/web/pgadmin/static/js/generated/ /pgadmin4/pgadmin/static/js/generated/
-COPY --from=docs-builder /pgadmin4/docs/en_US/_build/html/ /pgadmin4/docs/
-
-COPY ./pgadmin4/web /pgadmin4
-COPY ./run_pgadmin.py /pgadmin4
-COPY ./config_distro.py /pgadmin4
-
-RUN pip install --no-cache-dir -r requirements.txt
-
-# Precompile and optimize python code to save time and space on startup
-RUN python -O -m compileall /pgadmin4
-
-COPY ./entrypoint.sh /entrypoint.sh
-
 # Copy the PG binaries
 COPY --from=pg94-builder /usr/local/bin/pg_dump /usr/local/pgsql-9.4/
 COPY --from=pg94-builder /usr/local/bin/pg_dumpall /usr/local/pgsql-9.4/
@@ -98,6 +66,32 @@ COPY --from=pg11-builder /usr/local/bin/pg_dumpall /usr/local/pgsql-11/
 COPY --from=pg11-builder /usr/local/bin/pg_restore /usr/local/pgsql-11/
 COPY --from=pg11-builder /usr/local/bin/psql /usr/local/pgsql-11/
 
+WORKDIR /pgadmin4
+ENV PYTHONPATH=/pgadmin4
+
+#Copy in the docs and JS/CSS bundles
+COPY --from=node-builder /pgadmin4/web/pgadmin/static/js/generated/ /pgadmin4/pgadmin/static/js/generated/
+COPY --from=docs-builder /pgadmin4/docs/en_US/_build/html/ /pgadmin4/docs/
+
+# Install build-dependencies, build & install C extensions and purge deps in one RUN step
+# so that deps do not increase the size of resulting image by remaining in layers
+COPY ./pgadmin4/requirements.txt /pgadmin4
+RUN apk add --no-cache --virtual build-deps build-base postgresql-dev libffi-dev linux-headers && \
+    apk add postfix postgresql-client postgresql-libs && \
+    pip install --upgrade pip && \
+    pip install --no-cache-dir -r requirements.txt && \
+    pip install --no-cache-dir gunicorn && \
+    apk del --no-cache build-deps
+
+# Copy the code
+COPY ./pgadmin4/web /pgadmin4
+COPY ./run_pgadmin.py /pgadmin4
+COPY ./config_distro.py /pgadmin4
+COPY ./entrypoint.sh /entrypoint.sh
+
+# Precompile and optimize python code to save time and space on startup
+RUN python -O -m compileall /pgadmin4
+
 # Finish up
 VOLUME /var/lib/pgadmin
 EXPOSE 80 443