We often see devstack forums errors like this after pulling a new forum image:
How to reproduce
See that the ruby app did not start cleanly:
...and then restart the forum container.
Note that I've seen this happen even when having the most recent version of cs_comments_service checked out in my devstack directory. Brian Beggs and I have taken a quick, informal look at this before - it looked like the ansible forum scripts did the right thing, but maybe it needs another look. The problem is that a bundle install never happened in the freshly pulled image.
Determine where we need to fix this, either in configuration or in devstack, and then fix it.