AWS Certified Solutions Architect – Professional — Question 10

A Solutions Architect is working with a company that operates a standard three-tier web application in AWS. The web and application tiers run on Amazon EC2 and the database tier runs on Amazon RDS. The company is redesigning the web and application tiers to use Amazon API Gateway and AWS Lambda, and the company intends to deploy the new application within 6 months. The IT Manager has asked the Solutions Architect to reduce costs in the interim.
Which solution will be MOST cost effective while maintaining reliability?

Answer options

• A. Use Spot Instances for the web tier, On-Demand Instances for the application tier, and Reserved Instances for the database tier.
• B. Use On-Demand Instances for the web and application tiers, and Reserved Instances for the database tier.
• C. Use Spot Instances for the web and application tiers, and Reserved Instances for the database tier.
• D. Use Reserved Instances for the web, application, and database tiers.

Correct answer: B

Explanation

The correct answer is B because using On-Demand Instances for the web and application tiers allows flexibility and avoids the potential interruptions that may come with Spot Instances, while still utilizing Reserved Instances for the database tier to achieve cost savings. Options A and C introduce Spot Instances, which can lead to reliability issues due to their interruptible nature, and option D commits to Reserved Instances for all tiers, which could be unnecessarily costly during the transition period.