fix: forum connection to mongodb (again)

Turns out, the authentication mechanism should only be defined if there
is an actual authentication. For now, because of the urgency, we
hardcode this auth_mech to ":scram". We'll add a way to override it if
necessary, in the future.

CHANGELOG.md

@@ -4,6 +4,8 @@ Note: Breaking changes between versions are indicated by "💥".
 
 ## Unreleased
 
+- [Bugfix] Fix (agin) forum starting issue: "NoMethodError: undefined method `encode' for nil:NilClass".
+
 ## v12.1.1 (2021-09-17)
 
 - [Bugfix] Fix forum starting issue: "NoMethodError: undefined method `encode' for nil:NilClass".

tutor/templates/build/forum/Dockerfile

@@ -45,7 +45,7 @@ ENV NEW_RELIC_ENABLE false
 ENV API_KEY forumapikey
 ENV SEARCH_SERVER "http://elasticsearch:9200"
 ENV MONGODB_AUTH ""
-ENV MONGOID_AUTH_MECH ":scram"
+ENV MONGOID_AUTH_MECH ""
 ENV MONGODB_HOST "mongodb"
 ENV MONGODB_PORT "27017"
 ENV MONGODB_DATABASE "cs_comments_service"

tutor/templates/build/forum/bin/docker-entrypoint.sh

@@ -4,6 +4,12 @@ export MONGOHQ_URL="mongodb://$MONGODB_AUTH$MONGODB_HOST:$MONGODB_PORT/$MONGODB_
 # the search server variable was renamed after the upgrade to elasticsearch 7
 export SEARCH_SERVER_ES7="$SEARCH_SERVER"
 
+# make sure that there is an actual authentication mechanism in place, if necessary
+if [ -n "$MONGODB_AUTH" ]
+then
+    export MONGOID_AUTH_MECH=":scram"
+fi
+
 echo "Waiting for mongodb/elasticsearch..."
 dockerize -wait tcp://$MONGODB_HOST:$MONGODB_PORT -wait $SEARCH_SERVER -wait-retry-interval 5s -timeout 600s