There is a three-tier Web Application behind an Application Load Balancer. Auto Scaling Group is created for EC2 to dynamically scale-out when CPU utilization is higher than 75%. All these EC2 instances are spread across multiple AZ’s of the eu-central-1 region. The operational Director is looking for an aggregate CPU utilization for all EC2 instances part of this Auto Scaling group. Which of the following CloudWatch Metric setting can be done to meet this requirement?

Answer options:

A.Enable “CPU Utilization” metric for each EC2 instance in Auto Scaling Group & aggregate these values to get CPU utilization for all EC2 instances.
B.Enable “CPU Utilization” metric for each EC2 instance within each Availability zone for Auto Scaling Group to display aggregate CPU utilization for all EC2 instances.
C.Enable “CPU Utilization” metric for EC2 with dimension as “AutoScalingGroupName” to display aggregate CPU utilization for all EC2 instances.
D.Enable “CPU Utilization” metric for EC2 within each Availability Zone with dimension as “AutoScalingGroupName” to display aggregate CPU utilization for all EC2 instances.

Correct Answer: C
For getting an aggregate metric for all EC2 instances in an Auto Scaling group, dimension as “AutoScalingGroupName” can be used. In the above case, metric “CPUUtilization” can be set for EC2 instance with dimension as “AutoScalingGroupName” to aggregate CPU utilization for all EC2 instances across availability zones. The following are dimensions can be set for each metric.
AutoScalingGroupName
ImageId
InstanceId
InstanceType
Option A is incorrect as the aggregation of “CPU Utilization” for each EC2 Instance in an Auto Scaling Group is not required as the same can be displayed using AutoScalingGroupName Dimension.
Option B is incorrect as the aggregation of “CPU Utilization” for each EC2 Instance per Availability Zone in an Auto Scaling Group is not required. The same can be displayed using AutoScalingGroupName Dimension.
Option D is incorrect as there is no need to create Metrics per Availability Zone. While choosing dimension as Auto Scaling Group, it will select all EC2 instances in that group irrespective of Availability Zone.
For more information on Aggregating Statistics by Auto Scaling group, refer to the following URL-
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/GetMetricAutoScalingGroup.html