How do you scale a Node.js application?
Use cluster mode (multiple instances per CPU core via PM2 -i max or cluster module), load balancing (Nginx with multiple instances), caching (Redis for hot data), database optimization (indexes, query tuning), CDN for static assets, and microservices for independent scaling.
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More FAQs in Node.js Performance and Scaling Interview Questions Clusters, Streams, and Memory
Streams process data in chunks instead of loading everything into memory. Types: Readable, Writable, Duplex, Transform. Use fs.createReadStream instead of fs.readFile for large files to avoid out-of-memory errors. Pipe connects readable to writable streams.
Use worker_threads for in-process CPU work, child_process (fork) for separate scripts, or offload to a queue (Bull, SQS) processed by separate workers. Never run CPU-heavy tasks in the main event loop they block all other requests.
Monitor process.memoryUsage() periodically. Common causes: global variables accumulating data, event listeners not removed (use EventEmitter.setMaxListeners and off()), closures holding references, and timers not cleared (clearInterval/clearTimeout). Use heap snapshots and Chrome DevTools for debugging.
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