AWS Certified Solutions Architect – Associate (SAA-C03) — Question 903

A company recently migrated a monolithic application to an Amazon EC2 instance and Amazon RDS. The application has tightly coupled modules. The existing design of the application gives the application the ability to run on only a single EC2 instance.

The company has noticed high CPU utilization on the EC2 instance during peak usage times. The high CPU utilization corresponds to degraded performance on Amazon RDS for read requests. The company wants to reduce the high CPU utilization and improve read request performance.

Which solution will meet these requirements?

Answer options

• A. Resize the EC2 instance to an EC2 instance type that has more CPU capacity. Configure an Auto Scaling group with a minimum and maximum size of 1. Configure an RDS read replica for read requests.
• B. Resize the EC2 instance to an EC2 instance type that has more CPU capacity. Configure an Auto Scaling group with a minimum and maximum size of 1. Add an RDS read replica and redirect all read/write traffic to the replica.
• C. Configure an Auto Scaling group with a minimum size of 1 and maximum size of 2. Resize the RDS DB instance to an instance type that has more CPU capacity.
• D. Resize the EC2 instance to an EC2 instance type that has more CPU capacity. Configure an Auto Scaling group with a minimum and maximum size of 1. Resize the RDS DB instance to an instance type that has more CPU capacity.

Correct answer: A

Explanation

Because the application's architecture restricts it to running on a single EC2 instance, horizontal scaling is not an option; thus, vertical scaling (resizing) within an Auto Scaling group of size 1 is required to handle the CPU load. To resolve the database performance issue, configuring an RDS read replica allows the application to offload read queries from the primary database instance. Other options either attempt horizontal scaling of the EC2 instance which the application cannot support, or incorrectly route write traffic to a read-only replica.