does rails' multi db works with HA and global replication?

[luizkowalski]

I haven’t tried this yet because I don’t want to break production, but I wonder if anyone has done this:

HA will give you one primary and n replicas:

ID              STATE   ROLE    REGION  CHECKS              IMAGE                               CREATED                 UPDATED
e78423d1a33148  started replica iad     3 total, 3 passing  flyio/postgres-flex:15.3 (v0.0.46)  2024-01-03T15:35:20Z    2024-01-03T15:35:32Z
e2866756a37148  started replica iad     3 total, 3 passing  flyio/postgres-flex:15.3 (v0.0.46)  2024-01-03T15:45:44Z    2024-01-03T15:45:54Z
d891116b6505e8  started primary ewr     3 total, 3 passing  flyio/postgres-flex:15.3 (v0.0.46) 

Now, let’s say I have an app running in ewr and I would like to deploy another one in iad. would this database setup work?

production:
  primary:
    database: my_primary_database
    port: 5432
    hostname: top1.nearest.of.<postgres cluster app name>.internal
    username: postgres
    password: <%= ENV['ROOT_PASSWORD'] %>
  primary_replica:
    database: my_primary_database
    username: root_readonly
    hostname: top1.nearest.of.<postgres cluster app name>.internal
    password: <%= ENV['ROOT_READONLY_PASSWORD'] %>
    port: <%= ENV["PRIMARY_REGION"] == ENV["FLY_REGION"] ? 5432 : 5433 %>
    replica: true

I’m trying to think about all the scenarios and I think this would work without having to use fly-ruby (which seems abandoned?) and hijack the connection.

POST/PATCH/PUT would fall into the writer role and defaults to the primary database, regardless of their region and apps deploying in iad would read from the replica in iad. instances in ewrwould read/write from the primary

does that make sense, or am I missing something?