When Amazon API Gateway first appeared in 2015, the ways to build a serverless API were to run Flask or Express on EC2, or to use Elastic Beanstalk. API Gateway started out in the role of "a managed service that exposes a Lambda function as an HTTP endpoint", but over time it grew into a complete API management platform with authentication, caching, traffic control, and monitoring bolted on.
Today we dissect the internal structure of the REST API completely. From the moment a client sends an HTTP request, through the invocation of Lambda, to the response coming back — once you understand what every layer along that path does, 70% of the exam questions solve themselves.