An API Gateway is the single entry point for all client requests in a microservices architecture. It handles cross-cutting concerns like authentication, rate limiting, and request routing.
Why API Gateways?
Without Gateway:
┌────────┐ ┌─────────────┐
│ Client │────▶│ Service A │
└────────┘ └─────────────┘
│ ┌─────────────┐
└─────────▶│ Service B │
│ └─────────────┘
└─────────▶│ Service C │
└─────────────┘
Problems:
- Client knows all services
- No central auth/rate limiting
- Complex client logic
With Gateway:
┌────────┐ ┌─────────┐ ┌─────────────┐
│ Client │────▶│ Gateway │────▶│ Service A │
└────────┘ └─────────┘ ├─────────────┤
│ │ Service B │
│ ├─────────────┤
└─────────▶│ Service C │
└─────────────┘
Core Functions
Request Routing
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Authentication
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Rate Limiting
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Advanced Patterns
Request Aggregation (BFF Pattern)
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Response Transformation
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Circuit Breaker
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Request/Response Caching
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Service Discovery
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Implementation Options
Express Gateway
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Kong/NGINX
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Monitoring
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Conclusion
API Gateways simplify microservices architectures by centralizing cross-cutting concerns. Start with basic routing and authentication, then add caching, circuit breakers, and aggregation as needed.
Choose your implementation based on scale: Express with http-proxy-middleware for simple cases, Kong or AWS API Gateway for production systems.