If you're pushing the database up into the application layer, do you have to route all write operations through a single "master" application instance? If not, is there some multi-master scheme, and if so, is it cheaper to propagate state all the time than it is to have the application write to a master database instance over a network? Moreover, how does it affect the operations of your application? Are you still as comfortable bouncing an application instance as you would otherwise be?
The answer is: yes, you do have to write through a single primary application instance.
So far.
The two important things here are:
1. Fly.io makes it really easy to write through a single primary application instance
2. There are ways to solve this problem so your application doesn't have to worry about it.
Right now, you have to be a little careful bouncing app instances. If you bounce the writer, you can't perform writes for 15s or whatever. This is a big problem during deploys.
There are a tremendous number of Fly.io users that are fine with this limitation, though. It's pretty valuable for some segment of our customers right now.
