AWS Certified Solutions Architect – Professional — Question 479

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

Option B is correct because an AWS WAF rate-based rule automatically tracks and blocks client IP addresses that exceed a specified request threshold, requiring no manual intervention when the attacking IPs change weekly. Option D is operationally inefficient because it would require manually updating the IP set match rule every week as the 500 IP addresses rotate. Options A and C are incorrect because security groups do not support explicit deny rules, and managing dynamic IP blocks via AWS Firewall Manager would introduce significant operational overhead.