An API Gateway acts as a single entry point for API requests, handling routing, authentication, and cross-cutting concerns.
Key Responsibilities
Request Routing
- Routes requests to appropriate backend services
- Acts as reverse proxy
- Load balancing across service instances
Authentication & Authorization
- Centralized auth logic
- Token validation (JWT, OAuth)
- API key management
Cross-Cutting Concerns
- Rate limiting and throttling
- Request/response transformation
- Protocol translation (HTTP to gRPC, etc.)
- Response aggregation from multiple services
Observability
- Centralized logging
- Metrics collection
- Distributed tracing
- Request/response inspection
Benefits
- Simplified clients: Single endpoint instead of multiple service URLs
- Centralized policy enforcement: Auth, rate limiting in one place
- Backend flexibility: Change backend services without affecting clients
- Security: Internal services never directly exposed
Design Patterns
Lambda-Based API
From System Design:
API Gateway handles auth and routing, leaving Lambda to handle processing only. This design:
- Centralizes auth as configuration-based
- Minimizes compiled code in containers
- Reduces build time and artifact size
- Keeps Lambda code focused on business logic
Aggregation Pattern
- Gateway calls multiple services
- Combines responses
- Returns unified response to client
Challenges
- Single point of failure: Gateway must be highly available
- Performance bottleneck: All traffic flows through gateway
- Complexity: Can become monolithic if too much logic added
Popular Technologies
- Kong
- AWS API Gateway
- Azure API Management
- Traefik
- NGINX
References
See also: Microservices