AWS Certified Solutions Architect – Associate (SAA-C02) — Question 741

A company wants to reduce the cost of its existing three-tier web architecture. The web, application, and database servers are running on Amazon EC2 instances for the development, test, and production environments. The EC2 instances average 30% CPU utilization during peak hours and 10% CPU utilization during non- peak hours.
The production EC2 instances run 24 hours a day. The development and test EC2 instances run for at least 8 hours each day. The company plans to implement automation to stop the development and test EC2 instances when they are not in use.
Which EC2 instance purchasing solution will meet the company's requirements MOST cost-effectively?

Answer options

• A. Use Spot Instances for the production EC2 instances. Use Reserved Instances for the development and test EC2 instances.
• B. Use Reserved Instances for the production EC2 instances. Use On-Demand Instances for the development and test EC2 instances.
• C. Use Spot blocks for the production EC2 instances. Use Reserved Instances for the development and test EC2 instances.
• D. Use On-Demand Instances for the production EC2 instances. Use Spot blocks for the development and test EC2 instances.

Correct answer: B

Explanation

Production instances run continuously (24/7), making Reserved Instances the most cost-effective choice since they offer a significant discount for predictable, steady-state workloads. Development and test instances are stopped when not in use, so paying for Reserved Instances would result in wasted capacity, making On-Demand Instances combined with automation the most optimal choice. Spot Instances are unsuitable for production workloads due to the risk of interruption.