The Redis instances we're talking about here are "just" Fly.io apps; they're not like a special platform feature or anything. Which is good news; it means you can do whatever you want with Redis. You could, I guess, do a replica-of-replicas tree configuration, with app nodes holding connections (Redis connections are really cheap) to their local node, a macro-regional node, and the global node and selectively synchronizing. Or you could go the other way and lose some Redis servers, keeping Redis servers only in certain regions. We make it sort of straightforward for apps to suss out the topology with DNS queries.