What is an API Gateway and what problems does it solve?

API Gateway is the single entry point for all client requests to microservices. Functions: routing (to appropriate service), authentication/authorization (centralized), rate limiting, request/response transformation, aggregation (combine multiple services), caching, logging/monitoring, SSL termination. Benefits: client simplification, cross-cutting concerns centralized, backend service protection. Examples: Kong, AWS API Gateway, Apigee. Considerations: potential bottleneck, single point of failure (needs redundancy), added latency.