A user has set up Auto Scaling with ELB on the EC2 instances. The user wants to configure that whenever the CPU utilization is below 10%, Auto Scaling should remove one instance. How can the user configure this?

Answer options:

A.The user can get an email using SNS when the CPU utilization is less than 10%. The user can use the desired capacity of Auto Scaling to remove the instance.
B.Use CloudWatch to monitor the data and Auto Scaling to remove the instances using scheduled actions.
C.Configure a CloudWatch alarm in the execute policy that notifies the Auto Scaling Launch configuration when the CPU utilization is less than 10%, and configure the Auto Scaling policy to remove the instance.
D.Configure a CloudWatch alarm in the execute policy that notifies the Auto Scaling group when the CPU Utilization is less than 10%, and configure the Auto Scaling policy to remove the instance.

Answer – D
Option A is incorrect because for the user to get the notification, they have to configure CloudWatch which triggers a notification to Auto Scaling Group to terminate the instance. Updating the desired capacity will not work in this case.
Option B is incorrect because scheduled scaling is used to scale your application in response to predictable load changes, not upon any notification.
Option C is incorrect because the notification should be sent to Auto Scaling Group, not the launch configuration.
Option D is CORRECT because the notification is sent to Auto Scaling Group, removing an instance from the running instances.
More information on Auto Scaling, Scheduled Actions:
Auto Scaling helps you maintain application availability and allows you to scale your Amazon EC2 capacity up or down automatically according to conditions you define. You can use Auto Scaling to help ensure that you are running your desired number of Amazon EC2 instances. Auto Scaling can also automatically increase the number of Amazon EC2 instances during demand spikes to maintain performance and decrease capacity during lulls to reduce costs.
For more information on AutoScaling, please visit the link –
https://aws.amazon.com/autoscaling/
https://docs.aws.amazon.com/autoscaling/ec2/userguide/schedule_time.html