API Design Questions

Definition

Questions evaluating your ability to build API infrastructure that is secure, highly available, and scalable to millions of requests.

Explain Like I'm New

Can you design an architecture that survives going viral?

Real World Example

Designing the API layer for an Uber clone, discussing load balancers, rate limiting, geospatial database indexing, and WebSockets for live driver tracking.

Common Use Cases

•Staff Engineer Interviews

Terminal Output

bash / terminal

/* System Design Scenario: "Design a Rate Limiter for a public API." Answer: I would use a Token Bucket algorithm backed by Redis. 1. Every user gets a 'bucket' in Redis with 100 tokens, identified by their API Key. 2. When a request hits the API Gateway, it instantly checks Redis. 3. If tokens > 0, decrement by 1, and route the request to the backend. 4. If tokens == 0, the API Gateway immediately drops the request and returns a 429 Status Code, completely protecting the backend servers from doing any work. 5. A background process refills the bucket to 100 tokens every minute. */

Interview Questions

basic

Why should you put a Reverse Proxy / API Gateway (like NGINX or Cloudflare) in front of your Node.js API servers?

intermediate

How do you handle a sudden 10,000x spike in traffic to a Read-Heavy API endpoint?

Flash Cards

Question

Why Reverse Proxy?

Click to reveal answer

Answer

Node.js is great at logic, but terrible at heavy network tasks like SSL/HTTPS decryption, serving static images, and blocking DDoS attacks. A reverse proxy handles the heavy lifting, protects the real servers from direct internet exposure, and acts as a Load Balancer to distribute traffic across multiple Node instances.

Question

Handle Read-Heavy traffic spike?

Click to reveal answer

Answer

Aggressive caching. Implement a CDN layer (like Cloudflare) to serve cached responses globally. Use an in-memory datastore (like Redis) on the backend so the API never has to touch the main SQL database for that endpoint.