AWS Certified Solutions Architect – Professional — Question 1008

A solutions architect is designing a data processing system that will use Amazon EC2 instances. Data that needs to be processed will wait in an Amazon Simple
Queue Service (Amazon SQS) queue. At least two data processing instances must run at all times.
Which combination of actions will meet these requirements MOST cost-effectively? (Choose two.)

Answer options

• A. Create a Spot Fleet with a target scaling policy that targets the acceptable backlog per instance. Request two On-Demand Instances for minimum capacity. Use Spot Instances for additional capacity.
• B. Purchase two Reserved Instances for the target platform and instance type in the target AWS Region.
• C. Create On-Demand Capacity Reservations for two instances for the target platform and instance type in the target AWS Region.
• D. Create an Auto Scaling group that uses Spot Instance requests. Configure the scaling policy to scale with the size of the SQS queue. Set the minimum value to 2.
• E. Provision two Dedicated Hosts. Configure AWS Batch to use Spot Instances to supply additional capacity.

Correct answer: A, B

Explanation

To guarantee that at least two instances run at all times cost-effectively, purchasing Reserved Instances (Option B) for the baseline capacity is the most economical choice, whereas On-Demand Capacity Reservations (Option C) do not offer discounts and Dedicated Hosts (Option E) are too expensive. For scaling beyond the baseline, using a Spot Fleet that combines On-Demand instances for the minimum capacity and Spot Instances for backlog-driven scaling (Option A) ensures high availability and cost savings, whereas relying solely on Spot Instances (Option D) could violate the minimum running instance requirement if Spot capacity is reclaimed.