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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? How does zero-downtime restart work with Node's cluster module or PM2, and why is it important for production deployments? What is the WorkerData option when creating a Worker, and how does it differ from communicating via postMessage() after creation? What is the difference in behavior between the 'primary' and 'worker' role in Node's cluster module regarding which code paths execute?
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Node.js › Clustering & Worker Threads

How do you handle an uncaught exception inside a specific cluster worker without taking down the entire application?

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Answer

Because each worker is an independent process, a crash doesn't directly crash the others -- but the crashed worker stops serving traffic until replaced. The primary should listen for 'exit' and fork a replacement, restoring capacity quickly while the error is still logged for investigation.
cluster.on('exit', (worker, code, signal) => {
  console.error(`Worker ${worker.process.pid} died. Forking a replacement.`);
  cluster.fork();
});
Real-world example A production cluster automatically forks a replacement worker within milliseconds of any crash, keeping total capacity roughly constant while alerting the on-call engineer to investigate.

Common follow-ups: What's the risk of a worker crashing and restarting in a tight loop if a bug is triggered by every request of a certain type?;How would you add backoff or a circuit-breaker to the fork-on-exit logic?

Error Handling;Deployment & Process Managers (PM2)
All 15 Clustering & Worker Threads questions