Elastic Block Store Quiz
You have configured an Auto-scaling group for which the minimum running instance is 2 and maximum running instance is 10. For the past 30 minutes, all five instances have been running at 100 CPU Utilization; however, the Auto Scaling group has not added any more instances to the group. What is the most likely cause for this? Choose 2 answers from the options given below.
A. You already have 20 on-demand instances running.
B. The Auto Scaling group’s MAX size is set atfive.
C. TheAuto Scaling group’s scale down policy is too high.
D. The Auto Scaling group’s scale up policy has not yet been reached.
A. & D.
Answer – A and D
By default, you can run up to 20 On-Demand EC2 instances. If you need more, you have to complete a requisition form and submit it to AWS.However in the question, we have already mentioned that MAX is set to 10. In that case option B is invalid and hence cannot be marked as an answer. But the question does not mention that the metric chosen for this Auto Scaling policy is CPUUtilization Metric. It could be DiskWrites or Network In/Out metric. Assuming the current set up is to do with a metric other than CPUUtilization we can choose option D as a right choice. In this scenario, we are only discussing about the non-functioning Scaling up process and not about the Scaling down scenario.This is explained in the AWS documentation:Depending on the instance types, some instance types only support up to 5 on-demand instances. However the maximum for most of the instance types are 20 on-demand instances. So based on that, Option A is .<number of instances> instance(s) are already running. Launching EC2 instance failed.Cause: The Auto Scaling group has reached the limit set by the DesiredCapacity parameter.Solution: Update your Auto Scaling group by providing a new value for the –desired-capacity parameter using the update-auto-scaling-group command.If you’ve reached your limit for the number of EC2 instances, you can request an increase. For more information, see AWS Service Limits.
For more information on troubleshooting Auto Scaling, please refer to the following link:
http://docs.aws.amazon.com/autoscaling/latest/userguide/ts-as-capacity.htmlThe link below provides information on EC2 instance limits:https://docs.aws.amazon.com/general/latest/gr/aws_service_limits.html#limits_ec2More information on limits of on-demand EC2 instances is available at:https://aws.amazon.com/ec2/faqs/#How_many_instances_can_I_run_in_Amazon_EC2
