AWS Certified Solutions Architect – Associate (SAA-C02) — Question 398

A company has an application that uses overnight digital images of products on store shelves to analyze inventory data. The application runs on Amazon EC2 instances behind an Application Load Balancer (ALB) and obtains the images from an Amazon S3 bucket for its metadata to be processed by worker nodes for analysis. A solutions architect needs to ensure that every image is processed by the worker nodes.
What should the solutions architect do to meet this requirement in the MOST cost-efficient way?

Answer options

• A. Send the image metadata from the application directly to a second ALB for the worker nodes that use an Auto Scaling group of EC2 Spot Instances as the target group.
• B. Process the image metadata by sending it directly to EC2 Reserved Instances in an Auto Scaling group. With a dynamic scaling policy, use an Amazon CloudWatch metric for average CPU utilization of the Auto Scaling group as soon as the front-end application obtains the images.
• C. Write messages to Amazon Simple Queue Service (Amazon SQS) when the front-end application obtains an image. Process the images with EC2 On- Demand instances in an Auto Scaling group with instance scale-in protection and a fixed number of instances with periodic health checks.
• D. Write messages to Amazon Simple Queue Service (Amazon SQS) when the application obtains an image. Process the images with EC2 Spot Instances in an Auto Scaling group with instance scale-in protection and a dynamic scaling policy using a custom Amazon CloudWatch metric for the current number of messages in the queue.

Correct answer: D

Explanation

Using Amazon SQS ensures that message processing is reliable and no images are missed, as messages persist in the queue until successfully processed. EC2 Spot Instances offer the most cost-efficient compute option for overnight batch processing compared to On-Demand or Reserved Instances. Scaling based on the SQS queue depth (backlog metric) combined with scale-in protection ensures the Auto Scaling group scales accurately without terminating instances that are actively processing images.