Use Cloudfront CDN for static assets in production environments (#699)

* Change STATIC_URL to Cloudfront in prod

* Set STATIC_URL when INSIGHTS_CLOUDGFRONT defined

* Use CLOUDFRONT_DOMAIN var instead

* Rename CLOUDFRONT to CDN in var name

* Initialize CDN_DOMAIN to None in base.py

analytics_dashboard/settings/base.py

@@ -461,3 +461,7 @@ LEARNER_API_LIST_DOWNLOAD_FIELDS = None
 ########## CACHE CONFIGURATION
 COURSE_SUMMARIES_CACHE_TIMEOUT = 3600  # 1 hour timeout
 ########## END CACHE CONFIGURATION
+
+########## CDN CONFIGURATION
+CDN_DOMAIN = None  # production will not use a CDN for static assets if this is set to a falsy value
+########## END CDN CONFIGURATION

analytics_dashboard/settings/production.py

@@ -43,3 +43,7 @@ FULL_APPLICATION_NAME = u'{0} {1}'.format(PLATFORM_NAME, APPLICATION_NAME)
 # Depends on DOCUMENTATION_LOAD_ERROR_URL, so evaluate at the end
 DOCUMENTATION_LOAD_ERROR_MESSAGE = 'This data may not be available for your course. ' \
                                    '<a href="{error_documentation_link}" target="_blank">Read more</a>.'.format(error_documentation_link=DOCUMENTATION_LOAD_ERROR_URL)
+
+# Use Cloudfront CDN for assets
+if CDN_DOMAIN:
+    STATIC_URL = 'https://' + CDN_DOMAIN + '/static/'