All 15 Clustering & Worker Threads questions
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What is the os.cpus() function used for when setting up clustering in a Node.js application? Why does Node.js provide a cluster module, given that a single Node.js process is single-threaded? 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

How does PM2's cluster mode compare to manually using Node's built-in cluster module directly in application code?

Intermediate

Answer

PM2's cluster mode achieves the same goal at the process-manager level, without needing cluster-aware application code, and additionally provides zero-downtime reloads, automatic restarts, and log aggregation that would need to be built manually with the raw cluster module.
pm2 start server.js -i max --name my-app

// server.js needs zero cluster-specific code
const app = express();
app.listen(3000);
Real-world example A team migrates from a hand-rolled cluster.js entry point to 'pm2 start server.js -i max', immediately gaining zero-downtime reloads without maintaining that logic themselves.

Common follow-ups: What does 'zero-downtime reload' mean operationally, and how does PM2 achieve it?;When would you still want the raw cluster module instead of PM2?

Deployment & Process Managers (PM2);Advanced Node.js
All 15 Clustering & Worker Threads questions