AWS Certified Solutions Architect – Professional (SAP-C02) — Question 514

A company is hosting an application on AWS for a project that will run for the next 3 years. The application consists of 20 Amazon EC2 On-Demand Instances that are registered in a target group for a Network Load Balancer (NLB). The instances are spread across two Availability Zones. The application is stateless and runs 24 hours a day, 7 days a week.

The company receives reports from users who are experiencing slow responses from the application. Performance metrics show that the instances are at 10% CPU utilization during normal application use. However, the CPU utilization increases to 100% at busy times, which typically last for a few hours.

The company needs a new architecture to resolve the problem of slow responses from the application.

Which solution will meet these requirements MOST cost-effectively?

Answer options

• A. Create an Auto Scaling group. Attach the Auto Scaling group to the target group of the NLB. Set the minimum capacity to 20 and the desired capacity to 28. Purchase Reserved Instances for 20 instances.
• B. Create a Spot Fleet that has a request type of request. Set the TotalTargetCapacity parameter to 20. Set the DefaultTargetCapacityType parameter to On-Demand. Specify the NLB when creating the Spot Fleet.
• C. Create a Spot Fleet that has a request type of maintain. Set the TotalTargetCapacity parameter to 20. Set the DefaultTargetCapacityType parameter to Spot. Replace the NLB with an Application Load Balancer.
• D. Create an Auto Scaling group. Attach the Auto Scaling group to the target group of the NLB. Set the minimum capacity to 4 and the maximum capacity to 28. Purchase Reserved Instances for four instances.

Correct answer: D

Explanation

Since the 20 current instances run at only 10% CPU during normal operations, a baseline of 4 instances (running at 50% CPU) is sufficient to handle the steady-state load across two Availability Zones. Purchasing 3-year Reserved Instances for these 4 baseline instances provides the maximum cost savings for the continuous workload. An Auto Scaling group configured to scale up to 28 instances during peak hours allows the application to dynamically handle the CPU spikes using On-Demand instances without paying for unused idle capacity during off-peak hours.