Question
A company has developed an application on AWS that will track inventory levels of vending machines and initiate the restocking process automatically. The company plans to integrate this application with vending machines and deploy the vending machines in several markets around the world. The application resides in a VPC in the us-east-1 Region. The application consists of an Amazon Elastic Container Service (Amazon ECS) cluster behind an Application Load Balancer (ALB). The communication from the vending machines to the application happens over HTTPS.
The company is planning to use an AWS Global Accelerator accelerator and configure static IP addresses of the accelerator in the vending machines for application endpoint access. The application must be accessible only through the accelerator and not through a direct connection over the internet to the ALB endpoint.
Which solution will meet these requirements?
- A. Configure the ALB in a private subnet of the VPC. Attach an internet gateway without adding routes in the subnet route tables to point to the internet gateway. Configure the accelerator with endpoint groups that include the ALB endpoint. Configure the ALB’s security group to only allow inbound traffic from the internet on the ALB listener port. Correct
- B. Configure the ALB in a private subnet of the VPC. Configure the accelerator with endpoint groups that include the ALB endpoint. Configure the ALB's security group to only allow inbound traffic from the internet on the ALB listener port.
- C. Configure the ALB in a public subnet of the VPC. Attach an internet gateway. Add routes in the subnet route tables to point to the internet gateway. Configure the accelerator with endpoint groups that include the ALB endpoint. Configure the ALB's security group to only allow inbound traffic from the accelerator's IP addresses on the ALB listener port.
- D. Configure the ALB in a private subnet of the VPC. Attach an internet gateway. Add routes in the subnet route tables to point to the internet gateway. Configure the accelerator with endpoint groups that include the ALB endpoint. Configure the ALB's security group to only allow inbound traffic from the accelerator's IP addresses on the ALB listener port.
Explanation
Option A is correct. An internal ALB in a private subnet has no public endpoint, so it cannot be reached directly from the internet; Global Accelerator can still use it as an endpoint. For Global Accelerator to route to an internal ALB, the VPC must have an internet gateway attached, but the subnet route tables do not need routes to it, so the ALB stays private. Global Accelerator preserves the client IP address, so the ALB's security group must allow the vending machines' traffic from the internet on the listener port. Option B lacks the required internet gateway. Options C and D add internet gateway routes (C also makes the ALB public), and filtering on the accelerator's IP addresses does not work because traffic arrives with the clients' source IP addresses.
