O Amazon API Gateway é um serviço gerenciado destinado a facilitar as coisas. Na página do produto:
Amazon API Gateway is a fully managed service that makes it easy for developers to create, publish, maintain, monitor, and secure APIs at any scale. With a few clicks in the AWS Management Console, you can create an API that acts as a “front door” for applications to access data, business logic, or functionality from your back-end services, such as workloads running on Amazon Elastic Compute Cloud (Amazon EC2), code running on AWS Lambda, or any web application.
No entanto, nada impede que você crie sua própria API usando qualquer combinação de seus outros recursos.