[bombcar]

Buried under another thread was this post: https://aws.amazon.com/builders-library/avoiding-fallback-in... which is the exact same issue - a cache miss was backed up by a direct query and it took down all of Amazon trying to display shipping times.

grok say complexity bad

Fallback is not always necessary (sometimes it is, you can't just say "whelp the engines on this plane went out, time to die") but when you have a fallback system you should think about why you have it and how bad it is to fail, and if it could be worse to succeed.