How I Scaled a Legacy Node.js App to Handle 40k+ Long-Lived WebSocket Connections

Upgrading Project X — a legacy WebSocket application — revealed the pitfalls of scaling real-time systems without centralized state management. By introducing Redis as a distributed store and message broker, the author eliminated sticky-session dependency, enabled seamless cross-instance communication, and achieved stateless scalability. The article details the full implementation process, from connection lifecycle handling to message routing and fault-tolerant architecture, offering developers a practical roadmap for scaling WebSocket infrastructures efficiently.