API Gateway

The bouncer, the receptionist, and the translator. It decouples your messy backend microservices from the clean public-facing API.

What you will learn

• Understand why Microservices need a Gateway (Facade Pattern)
• Distinguish Gateway vs Load Balancer
• Master Cross-Cutting Concerns: Auth, Rate Limiting, SSL
• Implement Backends for Frontends (BFF) to optimize mobile performance

API gateways are a common interview checkpoint because they reveal whether you understand the difference between exposing one service and exposing a platform. As soon as multiple clients and multiple backend services exist, the edge layer becomes an architecture decision, not just a networking detail.

An API gateway is the client-facing control plane for your backend. It hides service topology, centralizes repeated policy decisions, and shapes requests before they reach internal services.

The gateway simplifies clients and centralizes cross-cutting concerns, but it also becomes a critical dependency. The more logic you push into it, the more valuable it becomes and the more dangerous it is to overload or misconfigure.

WARNING: Engineers often confuse a gateway with a load balancer. A load balancer spreads traffic across identical instances. A gateway applies application-level decisions like auth, routing, aggregation, and rate limiting across different services.

Open the API Gateway Simulator to see how authentication, routing, and rate limits interact on the edge. Then continue with Databases: SQL vs NoSQL to follow the request path deeper into the state layer.

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