I thought the problem with the previous approach was that configuring a separate cache for ourselves in settings.py was going to be ignored in production.  So why do we need a cache config here if it's going to be ignored?

Anyway, Django provides a Locmem config for the 'default' cache if we don't provide a CACHES setting at all, so leaving it out completely is equivalent to providing a Locmem config for 'default'.