An API Gateway sits between clients and microservices:
Responsibilities:
- Request routing to appropriate services
- Authentication and authorization
- Rate limiting and throttling
- Request/response transformation
- SSL termination
Benefits: Clients talk to one endpoint. Services don't handle cross-cutting concerns.
Examples: Kong, AWS API Gateway, Netflix Zuul.
Trade-off: Adds latency and becomes a potential bottleneck. Must be highly available.