Yes, it is. It's how we think about multi-region replication in our own tooling. It's not the only way to handle it (Cockroach would be an example of another approach; so would rqlite). We're not evangelists for multi-reader single-writer --- it's just the most common approach big Postgres shops tend to use, so we worked on making it effective. But the other approaches should work fine on Fly.io too.

What we especially like about multi-reader single-writer clusters is that you can mostly keep all the pieces in your head at the same time. If you understand Postgres or SQLite, and can get your head around the `fly-replay` header (which is just "replay this request over there please"), you've got the whole system.