All 15 Clustering & Worker Threads questions
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Why does Node.js provide a cluster module, given that a single Node.js process is single-threaded? How does PM2's cluster mode compare to manually using Node's built-in cluster module directly in application code? How do you pass data between the main thread and a worker thread using postMessage(), and what are the limits on what can be sent? What is the difference between the 'sticky' and default load-balancing strategies when using Node's cluster module, and when does it matter? What is the difference between the number of CPU cores and the optimal number of cluster workers for a given Node.js application? What is the difference between spawning a Worker Thread and spawning a Child Process for running a CPU-intensive JavaScript function? How do you gracefully terminate a worker thread, and what's the difference between worker.terminate() and letting it exit naturally? What happens to in-memory state (like an in-memory cache) when using the Node.js cluster module, and how do you handle this correctly? How do you use SharedArrayBuffer to share memory directly between Node.js worker threads, and what are the safety considerations? What is a worker thread pool, and why would you build one rather than creating a new Worker for every task?
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Node.js › Clustering & Worker Threads

What is the os.cpus() function used for when setting up clustering in a Node.js application?

Beginner

Answer

os.cpus() returns an array with one entry per logical CPU core available to the process -- its length is commonly used to decide how many workers to fork, letting code automatically scale its worker count to whatever hardware it runs on rather than hardcoding a fixed number.
console.log(os.cpus().length);
for (let i = 0; i < os.cpus().length; i++) cluster.fork();
Real-world example A startup script forks exactly as many workers as os.cpus().length reports, meaning the same code correctly utilizes all cores whether on a 2-core dev VM or a 32-core production server.

Common follow-ups: How does os.cpus().length behave inside a container with CPU limits below the host's core count?;What's a scenario where you'd deliberately fork fewer workers than the available core count?

Advanced Node.js;Docker & Containerization for Node.js
All 15 Clustering & Worker Threads questions