REST API with Amazon API Gateway: REST APIs are the appropriate choice for providing the frontend of the microservices application. Amazon API Gateway allows you to design, deploy, and manage REST APIs at scale. Amazon ECS in a Private Subnet: Hosting the application in Amazon ECS in a private subnet ensures that the containers are securely deployed within the VPC and not directly exposed to the public internet. Private VPC Link: To enable the REST API in API Gateway to access the backend services hosted in Amazon ECS, you can create a private VPC link. This establishes a private network connection between the API Gateway and ECS containers, allowing secure communication without traversing the public internet.

Question itself says: "The company must use REST APIs", hence WebSocket APIs are not applicable and such options are eliminated straight away.

AC are wrong as they are not REST API D, you don't make SG for API Gateway to EC2, you have to make a VPC Link. More details at https://docs.aws.amazon.com/apigateway/latest/developerguide/http-api-vpc-links.html

To allow the REST APIs to securely access the backend, a private VPC link should be created from API Gateway to the ECS containers. A private VPC link provides private connectivity between API Gateway and the VPC without using public IP addresses or requiring an internet gateway/NAT

https://docs.aws.amazon.com/apigateway/latest/developerguide/http-api-private-integration.html

A VPC link is a resource in Amazon API Gateway that allows for connecting API routes to private resources inside a VPC.

B is the right choice

Why Not D

b is right, bcs vpc link provided security connection