An auto-scaling group consists of certain EC2 instances. You noticed that few newly launched EC2 instances are not counted towards the Auto Scaling group`s aggregated metrics. Which of the following could be the best possible reason for this?

Answer options:

A.It`s because the warm-up period has not expired.
B.It`s because the Instances have not completed their boot sequence.
C.It`s because the Instances have not been attached to the Autoscaling Group.
D.It’s because the wrong launch configuration has been used.

Correct Answer: A
The AWS Documentation mentions the following.
With step scaling policies, you can specify the number of seconds that it takes for a newly launched instance to warm up. Until its specified warm-up time has expired, an instance is not counted toward the Auto Scaling group`s aggregated metrics. While scaling out, AWS also does not consider instances warming up as part of the group`s current capacity. Therefore, multiple alarm breaches that fall in the range of the same step adjustment result in a single scaling activity. This ensures that we don`t add more instances than you need.
Since this is clearly given in the AWS Documentation, all other options are invalid.
For more information on step scaling policy, please refer to the below URL-
https://docs.aws.amazon.com/autoscaling/ec2/userguide/as-scaling-simple-step.html#as-step-scaling-warmup