Design an API Gateway

An API Gateway acts as the single entry point for all client requests, essential for managing complexity in microservices. At Salesforce, where we handle massive volumes of customer data, the gateway must enforce strict security and performance standards. First, it handles Authentication and Authorization, ensuring only valid tokens reach backend services, often integrating with OAuth providers. Second, it manages Routing, directing requests to the correct service based on path or headers, which simplifies client-side logic. Third, Caching is crucial here; we can cache frequent read operations to reduce database load and improve response times significantly. Fourth, Metering allows us to track usage per tenant, enabling fair usage policies and billing integration. For implementation, I would recommend Envoy Proxy due to its dynamic configuration and robust observability features, though Nginx is excellent for simpler static setups. A custom service might be needed if we require complex request transformation that standard proxies cannot handle efficiently. By centralizing these concerns, we decouple business logic from infrastructure needs, allowing teams to deploy services independently while maintaining a unified, secure, and performant interface for our users.