How we migrated application servers from Unicorn to Puma

This post details the technical migration from Unicorn to Puma web servers. It explains the architectural differences between single-threaded (Unicorn) and multi-threaded (Puma) models, highlighting Puma's benefits for memory reduction (approx. 40%) and scalability. The post outlines the implementation steps, including experimental development use, setting up identical environments for testing, a phased rollout plan, and the resolution of specific issues like thread-safety with ChronicDuration and latency tuning. It also describes an upstream patch to Puma to address uneven capacity distribution. The results show a ~37% drop in memory usage.