API Gateway

gRPC, GraphQL & API Gateway Patterns

REST is the default API style, but it is not always the best fit. gRPC excels at internal microservice communication with its binary protocol, strong typing, and streaming support. GraphQL solves the over-fetching and under-fetching problems of REST by letting clients request exactly the data they need. API Gateways unify multiple backend services behind a single entry point. This lesson covers when and why to use each technology, how they work at a protocol level, and how to combine them in a real-world architecture.

Reverse Proxy & API Gateway

A reverse proxy sits at the edge of your infrastructure and terminates client connections so backends never see them directly. An API gateway is a reverse proxy with opinions: authentication, rate limiting, request transformation, and per-route policies. This lesson covers what each does, when one is enough and when you need the other, the canonical features (TLS termination, response caching, request shaping, JWT validation, circuit breaking), and the tools that implement them (NGINX, Envoy, Kong, AWS API Gateway, Apigee). By the end you can place either in a real architecture and articulate the boundary between them in an interview.

Design a Rate Limiter

Design a distributed rate limiter that protects an API platform from abuse and uneven load while staying fast and accurate at 1B requests per day. The interview centerpiece is choosing among the five canonical algorithms (fixed window, sliding window log, sliding window counter, token bucket, leaky bucket) and explaining how to make the chosen one atomic across a Redis cluster. We cover where to place the limiter (edge, gateway, in-process), per-IP vs per-user vs per-API-key keys, returning 429 with Retry-After, the hot key problem, and fail-open vs fail-closed under cache outages.