Where I work we use several different MySQL replicas in production, where we don't expect them to be in sync. So long as the source of truth (Master MySQL node

Where I work we use several different MySQL replicas in production, where we don't expect them to be in sync. So long as the source of truth (Master MySQL node) is up to date, it's okay. For example, if we show a user how much money is in their account on every page, we can run query that on a replica, since it's fine if this is a few seconds delayed. However, immediately after an action changed their balance, on a confirmation screen, we'd want to show the value from Master. It's entirely possible that any place elasticsearch is being used just don't need consistency.