Fundamentally we're talking about a load balancer. Even the most basic load-balancers can use a least-connections algorithm. Even a round-robin algorithm would

Fundamentally we're talking about a load balancer. Even the most basic load-balancers can use a least-connections algorithm. Even a round-robin algorithm would be better since that would give each dyno (number-of-dynos * msec per request) to finish a long-running request. Random routing is a viable option where the number of concurrent requests a node can handle is large or unknown, but when the limit is known and in the single-digits, random routing is a recipe for disaster.