APIs are the lingua franca of modern applications. With a microservices-based architecture, there are multiple services whose aggregated whole is the API set of the application. An API Gateway is the "front door" to this set of APIs .

API gateway responsibilities include the following:

• Authorization and access control: Ensures that only authorized applications are accessing the APIs
• Quotas/throttling: Enables quotes and rate limits for specific APIs from specific clients
• Monitoring
• API version management
• Reducing chattiness in a microservices architecture: Enables clients to call one endpoint, which, internally, can orchestrate across multiple backend microservices

There is a feature overlap between LBs and API gateways. Generally, the former focus more on efficient routing and the latter are more feature rich. We already had an detailed look at an API gateway in Chapter 7, Building APIs. The following diagram provides a quick recap: