AWS Certified Solutions Architect – Professional — Question 229

A company is running a web application with On-Demand Amazon EC2 instances in Auto Scaling groups that scale dynamically based on custom metrics. After extensive testing, the company determines that the m5.2xlarge instance size is optimal for the workload. Application data is stored in db.r4.4xlarge Amazon RDS instances that are confirmed to be optimal. The traffic to the web application spikes randomly during the day.
What other cost-optimization methods should the company implement to further reduce costs without impacting the reliability of the application?

Answer options

• A. Double the instance count in the Auto Scaling groups and reduce the instance size to m5.large.
• B. Reserve capacity for the RDS database and the minimum number of EC2 instances that are constantly running.
• C. Reduce the RDS instance size to db.r4.xlarge and add five equivalently sized read replicas to provide reliability.
• D. Reserve capacity for all EC2 instances and leverage Spot Instance pricing for the RDS database.

Correct answer: B

Explanation

Option B is the correct choice because reserving capacity for the RDS database and a minimum number of EC2 instances ensures cost savings while maintaining reliability. The other options either suggest increasing costs (A), potentially compromising application performance (C), or inappropriately applying Spot pricing to RDS which is not supported (D).