You are analyzing dynamic scaling activity defined to process messages from an Amazon SQS queue. You are using a target tracking policy. CloudWatch alarms are meant to invoke the scaling policy. However, you have noticed that the EC2 Auto Scaling group does not seem to be responding to a CloudWatch alarm. Which option may cause it?

Answer options:

A.Wrong CloudWatch metric is configured in the CloudWatch alarm.
B.The Auto Scaling group is under the cooldown period.
C.The minimum number of instances in the ASG is 0.
D.The desired number of instances in the ASG is 0.

Answer: B
The cooldown period is the amount of time to wait for a previous scaling activity to take effect is called the cooldown period.
Option A is incorrect because the CloudWatch alarm is already triggered so wrong CloudWatch metric does not cause the problem.
Option B is CORRECT because under the cooldown period, scaling activities will not be triggered.
Option C is incorrect because this option will not stop the ASG from adding/deleting instances.
Option D is incorrect because with the option, the ASG can still add/delete instances by adjusting the desired number of instances.
References:
https://docs.aws.amazon.com/autoscaling/application/userguide/application-auto-scaling-target-tracking.html