Omkar

System Design Series - Day 8/30 API Gateway Patterns – The Front Door of Your Microservices API Gateway is the single entry point for all your clients. Without it: - Mobile/web clients call 10+ different services directly - Authentication is duplicated everywhere - Rate limiting, CORS, logging → repeated in every service - Services are fully exposed to the internet With it: - One clean URL for clients - Centralized auth, rate limiting, routing, aggregation - Backend services stay hidden and secure Here’s everything you need to know about API Gateway patterns. What is an API Gateway? Think of it as the hotel front desk Without a front desk: - Guests wander around looking for rooms - No security check - Housekeeping and room service have no coordination With a front desk: - Single check-in point - Routes guests to correct room - Handles security, coordination, and requests API Gateway does exactly that for your microservices. The Problem It Solves Before API Gateway: Mobile app needs user profile + orders: → Calls User Service directly → Calls Order Service directly → Calls Payment Service directly Problems: - Client knows internal service URLs - Multiple network calls (slow on mobile) - Auth tokens sent to every service - No centralized rate limiting or logging - Services exposed to the internet After API Gateway: Mobile app calls one URL: https://api.example. com/profile Gateway handles everything internally: - Authenticates once - Routes and aggregates calls - Returns combined response Benefits: - 1 network call from client - Services completely hidden (security win) - Centralized cross-cutting concerns - Much better client experience Core Responsibilities: 1. Routing Maps external URLs to internal services GET /api/users → User Service GET /api/orders → Order Service 2. Authentication & Authorization Validates JWT/OAuth once at the gateway. Services trust the gateway. 3. Rate Limiting Prevents abuse (e.g., 100 requests/min per user). 4. Request Aggregation Combines multiple backend calls into one response for the client. 5. Protocol Translation Client uses REST → Service uses gRPC (handled at gateway). Advanced Patterns - Circuit Breaker → Prevents cascading failures when a service is down - Request/Response Transformation → Convert old → new API formats - Caching → Cache frequent responses at the gateway level - Logging & Monitoring → Centralized observability When to Use API Gateway Use it when: - You have multiple microservices - External clients (mobile, web, third-party) - You need centralized auth, rate limiting, or aggregation Don’t use it when: - Simple monolith (overkill) - Only internal service-to-service communication - Ultra-low latency is critical (extra hop) Popular Solutions - Kong (open-source, powerful plugins) - AWS API Gateway (managed, serverless) - NGINX + Lua (DIY, lightweight) - Traefik, Envoy, KrakenD Summary API Gateway is not just a proxy. It is the security layer, traffic manager, and aggregator for your entire backend. It simplifies client code, hides internal complexity, and centralizes cross-cutting concerns. Trade-offs: - Extra network hop (adds latency) - Becomes a critical component (make it highly available) Used correctly, it’s one of the most valuable pieces in any microservices architecture. Tomorrow (Day 9): Inter-Service Communication Patterns Questions about API Gateway? Drop them below 👇 #SystemDesign #APIGateway #Microservices #Backend