Stateless Node.js services: workers, shared state, and graceful shutdown

A Node process runs your JavaScript on a single event-loop thread, so using more cores and more machines means changing how the service is built. Each Question covers one piece: why instances must be stateless, cluster vs. worker_threads, moving sessions into Redis, what goes wrong with sticky sessions, draining connections on SIGTERM, liveness vs. readiness probes, and keeping CPU work off the event loop. The code and the libuv thread-pool details match current Node.