API Gateway
Build an API gateway with request routing, authentication, rate limiting, response caching, circuit breaker, and request/response transformation.
Overview
Create a Kong/AWS API Gateway-style service. Route incoming requests to backend microservices based on path and headers. Add cross-cutting concerns: JWT authentication, rate limiting per client, response caching, circuit breaker for failing upstreams, and request logging.
API gateways are the front door of every microservices architecture. They centralize cross-cutting concerns so individual services do not need to implement authentication, rate limiting, caching, and logging independently. Building one teaches you how requests flow through a production system and how each middleware layer adds value.
The middleware chain architecture is the core design pattern: each incoming request passes through a pipeline of auth, rate limit, cache, circuit breaker, and proxy stages. Each stage can short-circuit the pipeline (cache hit returns immediately, rate limit returns 429, circuit breaker returns 503) or enrich the request (auth adds user context, logging adds request ID). This pipeline pattern appears in every HTTP framework and understanding it deeply is essential for backend engineering.
For senior engineering interviews, API gateway architecture is a staple topic. Being able to explain and demonstrate: route matching with specificity, circuit breaker state machines, cache key generation and invalidation, and request/response transformation gives you concrete answers that distinguish you from candidates who can only draw boxes on a whiteboard.
Interview questions
- How does request routing work?
- How does the circuit breaker work?
- How should caching work?
- How do I handle request transformation?
- How do I implement health checks for upstream services?
- How do I implement load balancing across multiple instances?
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