Does the fly-replay header work for calls internal to Fly? For example, if one app hits another (local) app that hits a read-only Postgres replica, would the fly-replay header in the response cause the request to be replayed?
Not sure if this is a proxy-only feature or not. Apologies for not just testing this, hoping someone has the answer so I don’t have to set up the test cases. 
No worries. That’s a proxy-only feature. We’re working on bringing the proxy to the private network pretty soon though.
Any ETA on that? I’m thinking about moving a GraphQL gateway and some GraphQL services into Fly, but I want the ability to use read replicas for better performance outside of one region.
I suppose one workaround is to configure a read-write and read-only connection, but not the most ideal configuration.
With the gateway and services, the gateway would be at the proxy, and the services called by the gateway.