Node.js Developer interview question · Most asked
How do you scale a Node.js application?
Summary
Scale vertically by using all cores (cluster/PM2 or multiple containers) and horizontally by running many stateless instances behind a load balancer, with shared state in Redis/databases, caching and CDNs, and background work in queues.
Longer Answer
Keep instances stateless (no in-memory sessions), externalize WebSocket fan-out via pub/sub, and autoscale on CPU, latency or event loop lag. Profile before scaling: fixing a blocking hot path can be worth more than adding instances.
Key Points
- Use all cores (processes/containers)
- Stateless instances + LB
- Shared state in Redis/DB
- Queues for background work
More most-asked Node.js Developer questions
- Why is CPU-bound work a problem in Node.js and how do you handle it?
- What are streams in Node.js and what is backpressure?
- What is the difference between `process.nextTick`, Promise microtasks, `setImmediate` and `setTimeout(fn, 0)`?
- Explain the phases of the Node.js event loop.
- What is Node.js and why is it well suited to I/O-heavy servers?
- How has asynchronous code evolved in Node.js: callbacks, Promises and async/await?
- Walk through how an Express app handles a request, including errors from async handlers.
- What are the differences between CommonJS and ES modules in Node.js?