Questions 28 to 30

Explanations for questions 28 to 30

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Question 28

A web app allows users to upload images for viewing online. The compute layer that processes the images is behind an Auto Scaling group. The processing layer should be decoupled from the front end, and the ASG needs to dynamically adjust based on the number of images being uploaded.

How can this be achieved?

  1. Create an Amazon SNS Topic to generate a notification each time a message is uploaded. Have the ASG scale based on the number of SNS messages.
  2. Create a target tracking policy that keeps the ASG at 70% CPU utilization.
  3. Create an Amazon SQS queue and custom CloudWatch metric to measure the number of messages in the queue. Configure the ASG to scale based on the number of messages in the queue.
  4. Create a scheduled policy that scales the ASG at times of expected peak load.

Correct Answer: 3

Explanation: The best solution is to use Amazon SQS to decouple the front-end from the processing compute layer. To do this, you can create a custom CloudWatch metric that measures the number of messages in the queue and then configure the ASG to scale using a target tracking policy that tracks a certain value.

INCORRECT: “Create an Amazon SNS Topic to generate a notification each time a message is uploaded. Have the ASG scale based on the number of SNS messages.” is incorrect. The Amazon Simple Notification Service (SNS) is used for sending notifications using topics. Amazon SQS is a better solution for this scenario as it provides a decoupling mechanism where the actual images can be stored for processing. SNS does not provide a place for the images to be stored.

INCORRECT: “Create a target tracking policy that keeps the ASG at 70% CPU utilization.” is incorrect. Using a target tracking policy with the ASG that tracks CPU utilization does not allow scaling based on the number of images being uploaded.

CORRECT: “Create an Amazon SQS queue and custom CloudWatch metric to measure the number of messages in the queue. Configure the ASG to scale based on the number of messages in the queue.” is the correct answer.

INCORRECT: “Create a scheduled policy that scales the ASG at times of expected peak load.” is incorrect. Using a scheduled policy is less dynamic because although you may be able to predict usage patterns, it would be better to adjust dynamically based on actual usage.

References:

https://docs.aws.amazon.com/autoscaling/ec2/userguide/as-using-sqs-queue.html

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