I had pure active-active running at one job. We had our app layer centralize all its database access through a single set of wrapper generic SQL functions and h

I had pure active-active running at one job. We had our app layer centralize all its database access through a single set of wrapper generic SQL functions and had that set of functions implement some failures and hang-handling simple exponential backoff retry logic on the local DB before failing to the more remote one, with bidirectional. (nonpostgres) replication. You can indeed get into split brain situations and have to make hard choices as per the CAP theorem. And the replication will break sooner or later and you have to detect that and learn how to recover safely manually at least. Don't do it just for funsies. But it's definitely doable.