AWS Certified Solutions Architect – Associate (SAA-C03) — Question 147

A company runs a stateless web application in production on a group of Amazon EC2 On-Demand Instances behind an Application Load Balancer. The application experiences heavy usage during an 8-hour period each business day. Application usage is moderate and steady overnight. Application usage is low during weekends.
The company wants to minimize its EC2 costs without affecting the availability of the application.
Which solution will meet these requirements?

Answer options

• A. Use Spot Instances for the entire workload.
• B. Use Reserved Instances for the baseline level of usage. Use Spot instances for any additional capacity that the application needs.
• C. Use On-Demand Instances for the baseline level of usage. Use Spot Instances for any additional capacity that the application needs.
• D. Use Dedicated Instances for the baseline level of usage. Use On-Demand Instances for any additional capacity that the application needs.

Correct answer: B

Explanation

Option B is correct because it allows the company to use Reserved Instances for consistent, predictable traffic, thereby reducing costs, while leveraging Spot Instances for additional capacity during peak times. Options A, C, and D do not provide the same balance of cost savings and reliability. Option A relies solely on Spot Instances, which may not be available during peak usage; Option C does not utilize Reserved Instances, which are more cost-effective for consistent usage; and Option D uses Dedicated Instances, which are more expensive and unnecessary for this scenario.