AWS Certified Solutions Architect – Associate (SAA-C03) — Question 993

A company has an application that serves clients that are deployed in more than 20.000 retail storefront locations around the world. The application consists of backend web services that are exposed over HTTPS on port 443. The application is hosted on Amazon EC2 instances behind an Application Load Balancer (ALB). The retail locations communicate with the web application over the public internet. The company allows each retail location to register the IP address that the retail location has been allocated by its local ISP.

The company's security team recommends to increase the security of the application endpoint by restricting access to only the IP addresses registered by the retail locations.

What should a solutions architect do to meet these requirements?

Answer options

• A. Associate an AWS WAF web ACL with the ALB. Use IP rule sets on the ALB to filter traffic. Update the IP addresses in the rule to include the registered IP addresses.
• B. Deploy AWS Firewall Manager to manage the ALConfigure firewall rules to restrict traffic to the ALModify the firewall rules to include the registered IP addresses.
• C. Store the IP addresses in an Amazon DynamoDB table. Configure an AWS Lambda authorization function on the ALB to validate that incoming requests are from the registered IP addresses.
• D. Configure the network ACL on the subnet that contains the public interface of the ALB. Update the ingress rules on the network ACL with entries for each of the registered IP addresses.

Correct answer: A

Explanation

AWS WAF can be directly integrated with an Application Load Balancer to filter incoming traffic based on IP addresses using IP sets, which easily scale to accommodate thousands of entries. Network ACLs are not suitable because they have strict limits on the number of rules allowed (typically up to 40), making them incapable of handling 20,000+ individual IP addresses. Using Lambda functions with DynamoDB for basic IP filtering at the ALB level introduces unnecessary latency, complexity, and cost compared to native AWS WAF IP matching.