AWS Certified Solutions Architect – Professional (SAP-C02) — Question 278

An education company is running a web application used by college students around the world. The application runs in an Amazon Elastic Container Service (Amazon ECS) cluster in an Auto Scaling group behind an Application Load Balancer (ALB). A system administrator detects a weekly spike in the number of failed login attempts, which overwhelm the application's authentication service. All the failed login attempts originate from about 500 different IP addresses that change each week. A solutions architect must prevent the failed login attempts from overwhelming the authentication service.

Which solution meets these requirements with the MOST operational efficiency?

Answer options

• A. Use AWS Firewall Manager to create a security group and security group policy to deny access from the IP addresses.
• B. Create an AWS WAF web ACL with a rate-based rule, and set the rule action to Block. Connect the web ACL to the ALB.
• C. Use AWS Firewall Manager to create a security group and security group policy to allow access only to specific CIDR ranges.
• D. Create an AWS WAF web ACL with an IP set match rule, and set the rule action to Block. Connect the web ACL to the ALB.

Correct answer: B

Explanation

An AWS WAF rate-based rule is the most operationally efficient choice because it automatically blocks traffic from any individual IP address that exceeds a specified request threshold, dynamically mitigating the weekly spikes without manual intervention. In contrast, using IP set match rules or security groups would require constant updates to track the 500 changing IP addresses every week, which introduces administrative overhead. Restricting access to specific CIDR ranges is impractical for a global student population.