Configuring a Demand-Based Scaling Policy

An Auto Scaling group needs a scaling policy to determine when to perform scaling activities. Auto scaling policies work with CloudWatch to identify metrics and set alarms, which are triggered when the metrics fall outside of a specified value range. To configure a scale-based policy, you need to create the policy, and then create CloudWatch alarms to associate with the policy.In the following example, we will create a demand-based scaling policy.

For more information on CloudWatch, go to .

Create Auto Scaling Policies

To create the scaling policies:

Create a scale-out policy using the following command:

euscale-put-scaling-policy MyScaleoutPolicy --auto-scaling-group MyScalingGroup --adjustment=30 --type PercentChangeInCapacity

This command will return a unique Amazon Resource Name (ARN) for the new policy.

You will need this ARN to create the Cloudwatch alarms in subsequent steps.

The following example has been split into two lines for legibility.

arn:aws:autoscaling::706221218191:scalingPolicy:5d02981b-f440-4c8f-98f2-8a620dc2b787:
    autoScalingGroupName/MyScalingGroup:policyName/MyScaleoutPolicy

Create a scale-in policy using the following command:

euscale-put-scaling-policy MyScaleinPolicy -g MyScalingGroup --adjustment=-2  --type ChangeInCapacity

This command will return output containing a unique Amazon Resource Name (ARN) for the new policy, similar to the following:

You will need this ARN to create the Cloudwatch alarms in subsequent steps.

The following example has been split into two lines for legibility.

arn:aws:autoscaling::706221218191:scalingPolicy:d28c6ffc-e9f1-4a48-a79c-8b431794c367:
    autoScalingGroupName/MyScalingGroup:policyName/MyScaleinPolicy

Create CloudWatch Alarms

To create CloudWatch alarms:

Create a Cloudwatch alarm for scaling out when the average CPU usage exceeds 80 percent:

The following example has been split into multiple lines for legibility.

euwatch-put-metric-alarm AddCapacity  --metric-name CPUUtilization --unit Percent
--namespace "AWS/EC2" --statistic Average --period 120 --threshold 80 --comparison-operator 
GreaterThanOrEqualToThreshold --dimensions "AutoScalingGroupName=MyScalingGroup" 
--evaluation-periods 2 --alarm-actions 
arn:aws:autoscaling::706221218191:scalingPolicy:5d02981b-f440-4c8f-98f2-8a620dc2b787:
   autoScalingGroupName/MyScalingGroup:policyName/MyScaleoutPolicy

Create a Cloudwatch alarm for scaling in when the average CPU usage falls below 40 percent:

The following example has been split into multiple lines for legibility.

euwatch-put-metric-alarm RemoveCapacity --metric-name CPUUtilization --unit Percent
--namespace "AWS/EC2" --statistic Average  --period 120  --threshold 40  --comparison-operator 
LessThanOrEqualToThreshold  --dimensions "AutoScalingGroupName=MyScalingGroup" --evaluation-periods 2 
--alarm-actions 
 arn:aws:autoscaling::706221218191:scalingPolicy:d28c6ffc-e9f1-4a48-a79c-8b431794c367:
  autoScalingGroupName/MyScalingGroup:policyName/MyScaleinPolicy

Verify Your Alarms and Policies

Once you’ve created your Auto Scaling policies and CloudWatch alarms, you should verify them.To verify your alarms and policies:

Use the CloudWatch command euwatch-describe-alarms to see a list of the alarms you’ve created:

euwatch-describe-alarms

This will return output similar to the following:

AddCapacity	INSUFFICIENT_DATA	arn:aws:autoscaling::706221218191:scalingPolicy:5d02981b-f440-4c8f-98f2-8a620dc2b787:
   autoScalingGroupName/MyScalingGroup:policyName/MyScaleoutPolicy	
   AWS/EC2	CPUUtilization	120	Average	2	GreaterThanOrEqualToThreshold	80.0
RemoveCapacity	INSUFFICIENT_DATA	arn:aws:autoscaling::706221218191:scalingPolicy:d28c6ffc-e9f1-4a48-a79c-8b431794c367:
autoScalingGroupName/MyScalingGroup:policyName/MyScaleinPolicy	
   AWS/EC2	CPUUtilization	120	Average	2	LessThanOrEqualToThreshold	40.0

Use the euscale-describe-policies command to see the scaling policies you’ve created:

euscale-describe-policies --auto-scaling-group MyScalingGroup

This will return output similar to the following (note that this output has been split into multiple lines for legibility):

SCALING-POLICY	MyScalingGroup	MyScaleinPolicy	-2	ChangeInCapacity	arn:aws:autoscaling::706221218191:
  scalingPolicy:d28c6ffc-e9f1-4a48-a79c-8b431794c367:
  autoScalingGroupName/MyScalingGroup:policyName/MyScaleinPolicy
SCALING-POLICY	MyScalingGroup	MyScaleoutPolicy	30	PercentChangeInCapacity	arn:aws:autoscaling::706221218191:
  scalingPolicy:5d02981b-f440-4c8f-98f2-8a620dc2b787:
  autoScalingGroupName/MyScalingGroup:policyName/MyScaleoutPolicy