Advanced REST API Interview and System Design
Consolidate the course through advanced design questions and architecture scenarios.
Core Interview Questions
You should be able to explain:
- What REST means.
- REST constraints.
- Statelessness.
- Resource vs representation.
- Safe vs idempotent methods.
- PUT vs PATCH.
- POST vs PUT.
- 401 vs 403.
- 400 vs 422.
- 409 conflicts.
- 201 vs 202 vs 204.
- Headers and content negotiation.
- Caching and ETags.
- CORS and CSRF.
- Authentication vs authorization.
- JWT limitations.
- OAuth 2.0 vs OpenID Connect.
- RBAC vs ABAC.
- Cursor vs offset pagination.
- HATEOAS.
- API versioning.
- Rate limiting.
- Webhooks and idempotency.
- Retries and backoff.
- Interview answers should explain trade-offs rather than memorize definitions.
- HTTP semantics are a recurring foundation for advanced API questions.
- Security questions often test authorization boundaries rather than authentication alone.
REST API System Design Questions
System Design
For an API system-design interview, start with requirements and traffic assumptions. Define resources and core workflows. Establish authentication and authorization. Design request and response contracts. Decide pagination, filtering, sorting, caching, rate limiting, and idempotency. Then design the data layer, queues, object storage, gateway, scaling strategy, observability, and failure handling.
Always discuss bottlenecks and failure modes.
For example, when designing an API that accepts millions of uploads, do not send all file bytes through application servers. Use signed object-storage uploads, metadata APIs, asynchronous processing, queues, and lifecycle policies.
Final Mastery Checklist
REST API Mastery
You have completed the conceptual path from HTTP to production architecture.
You should now be able to take a requirement such as "build an API for an e-commerce platform" and reason through the entire lifecycle:
Domain → resources → URIs → HTTP methods → representations → validation → authentication → authorization → errors → pagination → caching → concurrency → versioning → HATEOAS → security → asynchronous processing → webhooks → testing → documentation → observability → scaling → resilience → deployment.
The most important transition is from thinking in terms of "which endpoint should I create?" to thinking in terms of contracts, resources, state transitions, invariants, security boundaries, failure modes, and operational behavior.
That is the difference between implementing a few REST endpoints and engineering a production API.
- REST is an architectural style built around constraints.
- HTTP semantics are foundational to good REST API design.
- HATEOAS is part of the REST uniform-interface constraint.
- Security, reliability, and observability must be designed into the API.
- A good API is a stable contract between independently evolving systems.
What is the most important mindset for designing a mature REST API?