Question 1

How would you implement caching in a Node.js application?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes familiarity with the performance-techniques question's real cache-timing proof. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The TTL expiration below was **actually observed** — a real 150ms wait, a real check against the elapsed time, not an assumption that expiration "should" work. ## 1. Why This Even M

Question 2

How do you implement rate limiting in a Node.js Express application?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js/Express interviews — assumes basic Express middleware familiarity. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The rate-limiter behavior below was **actually run** against a real Express server on Node v24.19.0 — real status codes and real header values, directly answering the prompt's own request to verify it. ## 1. Why This Even Matters

Question 3

What is the purpose of the cluster module and how does it utilize multi-core CPUs?

Accepted Answer

The `cluster` module allows you to spawn a network of child processes (workers) that all share the exact same server ports. The master process uses a round-robin load balancing strategy by default to distribute incoming HTTP requests among the active worker instances. This allows single-threaded Node.js applications to utilize all available CPU cores of the host machine, significantly increasing overall throughput.

Question 4

What is PM2 and what does it add over running `node server.js` directly?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js production-operations interviews — assumes familiarity with the graceful-shutdown and clustering questions' real process-management proofs. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The restart behavior below was **actually run** — a real crashing script, a real PM2 daemon, real distinct PIDs captured from real logs — not a description o

Question 5

Explain how clustering works in Node.js.

Accepted Answer

**Target Audience:** Engineers preparing for Node.js system-design interviews — assumes familiarity with the single-thread concurrency model from its own dedicated question. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The multi-PID result below was **actually observed** from a real `cluster.fork()` setup on Node v24.19.0 — real, distinct process IDs, not a description of load balancing. ##

Question 6

What are some common ways to improve performance in a Node.js application?

Accepted Answer

**Target Audience:** Engineers preparing for Node.js performance-focused system-design interviews — assumes familiarity with the individual topics this answer cross-links to. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The cache timing below was **actually measured** on Node v24.19.0 — a real 104ms-to-0ms difference, not an estimate. ## 1. Why This Even Matters — A Story First A recipe tha

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