Thank you for the insight. 3, 4 and 5 are probably the reasons why they don't do it. They could, but it would be harder to operate, a bit more expensive and a l

Thank you for the insight. 3, 4 and 5 are probably the reasons why they don't do it. They could, but it would be harder to operate, a bit more expensive and a lot less elastic. And maybe some customers at some points in time are, in fact, too large for that strategy. As for 1, they do use ELB now, I don't know if they did during the "intelligent routing" era. It is only possible to create up to 10 different ELBs with a standard AWS account, but something as large as Heroku does not have the same limits. I don't really understand point 2, could you explain what you mean? I can see how keep-alive can be a problem with some configurations but if you use the DNS to select the shard it shouldn't be a problem (you have one balancer per shard, with ELB it means different CNAME targets).