API gateway vs internet gateway

The main difference between API Gateway and Internet Gateway is:

API Gateway is an AWS service that allows developers to create, publish, maintain, monitor, and secure APIs at any scale. It sits between the front-end (clients) and back-end (servers, databases, Lambda functions etc) of an application. Some key capabilities of API Gateway include:

• It acts as a reverse proxy and load balancer. It handles traffic management, authorization and access control for APIs.
• It supports creation of RESTful and WebSocket APIs. RESTful APIs can be used to access backends like EC2 instances, Lambda functions etc. WebSocket APIs enable real-time communication.
• It provides features like throttling, caching, monitoring, authentication, authorization etc for APIs. SDKs can also be generated.

Internet Gateway is a separately billed AWS service that allows communication between instances in VPCs and the internet. It allows instances in private subnets of a VPC to connect to the internet, but not to each other or to instances in public subnets. The internet gateway sits at the edge of a VPC and routes internet-bound traffic to the internet and vice versa.

Please refer: API Gateway- https://docs.aws.amazon.com/apigateway/latest/developerguide/welcome.html, Internet Gateway- https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Internet_Gateway.html