For Ruby apps, specially, you need to set the primary region in the app so POST requests are routed to an instance in the primary region, while GET requests could be handled in the servers in other regions
Personally, I’d disable
autoscale
as it has been on life-support ever since Fly shifted its focus to Apps v2 (aka Machines).
Ok, I guess I will do that then, wait for the Autoscaling apps on machines that was mentioned in one of the links you posted