Amazon API Gateway is a fully managed service that makes it easy for developers to publish, maintain, monitor, and secure APIs at any scale. Create an API to access data, business logic, or functionality from your back-end services, such as applications running on Amazon Elastic Compute Cloud (Amazon EC2), code running on AWS Lambda, or any web application.

Developer Guide
Provides a conceptual overview of Amazon API Gateway and includes detailed instructions for using the service.
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API Reference
Describes all the Amazon API Gateway operations in detail. Also provides sample requests, responses, and errors for the supported web services protocols.