Reduce openedx image size with static asset deduplication

This is inspired from FUN's openedx-docker project: static files are
de-duplicated with rdfind to reduce the uncompressed image size by
320Mb.

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 Note: Breaking changes between versions are indicated by "💥".
 
+## Unreleased
+
+- [Improvement] Reduce "openedx" Docker image size with static asset de-duplication
+
 ## v10.2.1 (2020-08-27)
 
 - [Bugfix] Upgrade all services to open-release/juniper.3

tutor/templates/build/openedx/Dockerfile

@@ -111,7 +111,7 @@ RUN npm install --verbose --registry=$NPM_REGISTRY
 FROM minimal as production
 
 # Install system requirements
-RUN apt install -y gettext gfortran graphviz graphviz-dev libffi-dev libfreetype6-dev libgeos-dev libjpeg8-dev liblapack-dev libmysqlclient-dev libpng12-dev libsqlite3-dev libxmlsec1-dev lynx ntp pkg-config \
+RUN apt install -y gettext gfortran graphviz graphviz-dev libffi-dev libfreetype6-dev libgeos-dev libjpeg8-dev liblapack-dev libmysqlclient-dev libpng12-dev libsqlite3-dev libxmlsec1-dev lynx ntp pkg-config rdfind \
 && rm -rf /var/lib/apt/lists/*
 
 COPY --from=dockerize /usr/local/bin/dockerize /usr/local/bin/dockerize
@@ -177,7 +177,9 @@ RUN openedx-assets xmodule \
     && openedx-assets common
 COPY ./themes/ /openedx/themes/
 RUN openedx-assets themes \
-    && openedx-assets collect --settings=tutor.assets
+    && openedx-assets collect --settings=tutor.assets \
+    # De-duplicate static assets with symlinks
+    && rdfind -makesymlinks true -followsymlinks true /openedx/staticfiles/
 
 # Create a data directory, which might be used (or not)
 RUN mkdir /openedx/data