AWS Certified Solutions Architect – Associate (SAA-C03) — Question 673

A company runs a highly available web application on Amazon EC2 instances behind an Application Load Balancer. The company uses Amazon CloudWatch metrics.

As the traffic to the web application increases, some EC2 instances become overloaded with many outstanding requests. The CloudWatch metrics show that the number of requests processed and the time to receive the responses from some EC2 instances are both higher compared to other EC2 instances. The company does not want new requests to be forwarded to the EC2 instances that are already overloaded.

Which solution will meet these requirements?

Answer options

• A. Use the round robin routing algorithm based on the RequestCountPerTarget and ActiveConnectionCount CloudWatch metrics.
• B. Use the least outstanding requests algorithm based on the RequestCountPerTarget and ActiveConnectionCount CloudWatch metrics.
• C. Use the round robin routing algorithm based on the RequestCount and TargetResponseTime CloudWatch metrics.
• D. Use the least outstanding requests algorithm based on the RequestCount and TargetResponseTime CloudWatch metrics.

Correct answer: B

Explanation

The Application Load Balancer (ALB) supports the least outstanding requests routing algorithm, which shifts traffic away from overloaded targets by routing new requests to instances with the fewest active connections. Monitoring the RequestCountPerTarget and ActiveConnectionCount CloudWatch metrics helps identify this imbalance and validates the need for this routing change. Round-robin routing distributes requests evenly without considering the current load of the instances, which would fail to prevent overloaded instances from receiving new traffic.