How does clustering differ from using Worker Threads in Node.js?

0-2 years experience

1. 1You need to handle CPU‑bound image processing in a small Express endpoint. Would you use the cluster module or Worker Threads, and why?
2. 2If you start a Node.js app with `node --cluster` and then spawn a Worker Thread inside one of the workers, what happens to the number of processes and threads?
3. 3How would you share a simple in‑memory cache between multiple workers created with the cluster module versus using Worker Threads?

2-5 years experience

1. 1Your team added a new feature that does heavy JSON parsing on incoming requests, and the service started to show latency spikes. Walk me through how you would decide whether to refactor using clustering or Worker Threads.
2. 2During a load test, you notice that using the cluster module gives you good throughput but memory usage doubles. Switching to Worker Threads reduces memory but you see occasional deadlocks. Explain what could be causing these symptoms.
3. 3You deployed a Node.js microservice using the cluster module behind a load balancer, but after a rolling restart some requests fail with `ECONNRESET`. How would you debug whether the issue is related to clustering vs thread usage?

5-8 years experience

1. 1Design a high‑throughput real‑time analytics pipeline in Node.js. Compare the architectural implications of using a clustered set of processes versus a pool of Worker Threads for the compute stage.
2. 2Your legacy service runs on a cluster of processes and you need to migrate to Worker Threads to reduce container footprint. What migration steps, compatibility concerns, and performance regressions would you anticipate?
3. 3Explain how error handling, graceful shutdown, and resource cleanup differ between a cluster of processes and a pool of Worker Threads in a production Node.js service.

8+ years experience

1. 1At a company‑wide level you need to standardize how CPU‑bound work is offloaded across many services. What criteria would you set to decide when a team should use clustering versus Worker Threads, considering deployment, observability, and operational overhead?
2. 2Your organization is moving from VM‑based deployments to serverless containers that limit the number of processes per pod. How would this shift affect the choice between clustering and Worker Threads for existing Node.js services?
3. 3Discuss the long‑term maintenance implications of building a shared library that abstracts over clustering and Worker Threads, including versioning, testing, and cross‑team onboarding.