A Tune challenge from Foundations. Every so often a crowd arrives at once: for two seconds, four times the usual traffic. Almost a third of the requests in each rush are lost. Lose fewer than 1 in 100, keep 99 out of 100 under 600 ms, and spend as little as you can.
The design you start with: p99 111ms, 0% of requests failing, 8.9/s answered.