Two things:

1. Essentially every RDBMS except MySQL has a RETURNING clause, so you can read your write essentially for free (and even MySQL lets you read the auto-increment value it inserted).

2. Barring that, how is this finicky to get right? If you get an ack back from the DB, assuming you haven’t done silly things to fsync settings, it’s written. It’s durable. So, within the same try/except or similar, take what you just told it to write, and use it. If you don’t get an ack back, it did not write, so don’t use what you had stored.

You'd have to reach the same instance for your next request. Easier to just tell clients that they get returned a header that they should attach to their requests so the backend can route their reads to the primary for some time until replication caught up.