Node.js runs on a single thread by default, which means a single CPU-intensive task can block all requests and multi-core systems are underutilized. With over 12 years of Node.js development experience since 2014 and as the creator of CoreUI, I’ve scaled numerous APIs to handle thousands of concurrent requests. The cluster module allows you to spawn multiple worker processes that share the same server port, distributing load across all CPU cores. This approach dramatically improves throughput and provides automatic restart capability when workers crash.