AWS Certified Solutions Architect – Associate (SAA-C02) — Question 202

A company runs a production application on a fleet of Amazon EC2 instances. The application reads the data from an Amazon SQS queue and processes the messages in parallel. The message volume is unpredictable and often has intermittent traffic. This application should continually process messages without any downtime.
Which solution meets these requirements MOST cost-effectively?

Answer options

• A. Use Spot Instances exclusively to handle the maximum capacity required.
• B. Use Reserved Instances exclusively to handle the maximum capacity required.
• C. Use Reserved Instances for the baseline capacity and use Spot Instances to handle additional capacity.
• D. Use Reserved Instances for the baseline capacity and use On-Demand Instances to handle additional capacity.

Correct answer: D

Explanation

Option D is correct because it provides a stable baseline with Reserved Instances while allowing for flexible scaling with On-Demand Instances to accommodate traffic spikes, ensuring continuous operation. Option A is not ideal as Spot Instances can be interrupted, leading to potential downtime. Option B does not allow for flexibility in handling intermittent traffic, and Option C, while better than A, still risks interruptions due to the nature of Spot Instances.