worker-threads vs cluster: When to Use Which, With Reasoning Node.js is single-threaded. That's the first thing everyone learns. But at some point you realize okay, single-threaded is fine for most things. But what happens when your app needs to actually use more than one CPU core? Or what happens when one heavy task starts blocking everything else? That's where worker-threads and cluster both show up. And for a while I treated them like they solve the same problem. They don't. The way I started