Surviving Flashes of High-Write Traffic Using Scriptable Load Balancers (Part II) - Shopify

What this post added

This post details the implementation of stateless fair queueing using PID controllers to manage high-write traffic during flash sales. It introduces a mechanism to assign priority based on user timestamps, using a dynamically calculated threshold managed by a proportional PID controller. This approach avoids a central data store, maintaining statelessness at the edge tier and significantly reducing queue time variance, as evidenced by improved P95, average, and median queue times.