[fizx]

Right now, heroku has one inbound load-balancer that's out of their control (probably ELB(s)). This load balancer hits another layer of mesh routers that heroku does control, and that perform all of herokus magic. In order for "intelligent routing," which is more commonly known as "least-conn" routing to work amongst the mesh layer, all of the mesh routers would have to share state with each other in real-time, which makes this a hard problem.

Alternately, heroku can introduce a third layer between the mesh routers and the inbound random load balancer. This layer consistently hashes (http://en.wikipedia.org/wiki/Consistent_hashing) the api-key/primary key of your app, and sends you to a single mesh router for all of your requests. Mesh routers are/should be blazing fast relative to rails dynos, so that this isn't really a bottleneck for your app. Since the one mesh router can maintain connection state for your app, heroku can implement a least-conn strategy. If the mesh router dies, another router can be automatically chosen.