App servers should have a fast access to data! Which either means running caches alongside the app servers, or doing clever things with databases.

We just released a preview Postgres + regional replicas. This setup keeps the postgres leader in one region and lets people add replicas in other regions they're interested in. It works really well for typical full stack apps.

We've also found a surprising number of customers who want to run in only one specific region. They don't spread apps out geographically, they just have a concentrated population of users in, say, Sydney. We're increasingly becoming "Heroku for <region>".