Comment by eithed

Client network timeout shouldn't result in 500. With 408 and retry you should, dependent on the business criteria, get either an upsert (transaction is retried) or 422 (validation that given entry already exists).

Even if it's "DB in datacenter I tried to save to was hit by meteor" event, you can cater for this not to result in 500 (ie - DB unreachable, retry in a couple of minutes); the question is if you want to.