AWS Certified Solutions Architect – Associate (SAA-C02) — Question 355

A company runs an application that uses multiple Amazon EC2 instances to gather data from its users. The data is then processed and transferred to Amazon S3 for long-term storage. A review of the application shows that there were long periods of time when the EC2 instances were not being used. A solutions architect needs to design a solution that optimizes utilization and reduces costs.
Which solution meets these requirements?

Answer options

• A. Use Amazon EC2 in an Auto Scaling group with On-Demand instances.
• B. Build the application to use Amazon Lightsail with On-Demand Instances.
• C. Create an Amazon CloudWatch cron job to automatically stop the EC2 instances when there is no activity.
• D. Redesign the application to use an event-driven design with Amazon Simple Queue Service (Amazon SQS) and AWS Lambda.

Correct answer: A

Explanation

Integrating Amazon EC2 Auto Scaling allows the infrastructure to dynamically scale the number of running instances up or down based on actual user demand, which eliminates paying for idle capacity during low-activity periods. Amazon Lightsail is not designed for dynamic scaling of this nature, and using a CloudWatch cron job to stop instances is too rigid to handle unpredictable user traffic spikes. While an event-driven architecture is highly efficient, adopting an Auto Scaling group optimizes the existing EC2-based application's utilization with minimal refactoring.