Re the distribution, absolutely. That "FIFTY TIMES" is totally due to the width of the distribution. Although, you know, even if their app was written such that every single request took exactly 100ms of dyno time, this random routing would create the problem all over again, to some degree.

As for the intelligent routing, could you explain the problem? The goal isn't to predict which request will take a long time, the goal is to not give more work to dynos that already have work. Remember that in the "intelligent" model it's okay to have requests spend a little time in the global queue, a few ms mean across all requests, even when there are free dynos.

Isn't it as simple as just having the dynos pull jobs from the queue? The dynos waste a little time idle-spinning until the central queue hands them their next job, but that tax would be pretty small, right? Factor of two, tops? (Supposing that the time for the dyno-initiated give-me-work request is equal to the mean handling time of a request.) And if your central queue can only handle distributing to say 100 dynos, I can think of relatively simple workarounds that add another 10ms of lag every factor-of-100 growth, which would be a hell of a lot better than this naive routing.

What am I missing?