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Auto Scaling with Alarms and Load Balancing

In this example, you set up an Amazon EC2 application to be load-balanced and auto-scaled with a minimum number of two instances and maximum number of twenty instances. Auto Scaling in this example is configured to scale out by one when the application’s average CPU usage exceeds a threshold of 80 percent for 10 minutes, and scale in by one when the application's average CPU usage drops below 40 percent for 10 minutes. You use Amazon CloudWatch alarms to alert the application when a threshold is breached.

This example assumes that you have the following:

An Amazon Machine Image (AMI) for your Amazon EC2 application
A defined LoadBalancer named MyLB configured for Availability Zones us-east-1a and us-east-1b
Installed Amazon CloudWatch command line tools if you're planning on using the command line interface.

	Note
	For information on how to create an AMI, go to Creating Your Own AMIs in the Amazon Elastic Compute Cloud User Guide. For more information about Elastic Load Balancing, go to the Elastic Load Balancing Developer Guide. For information on installing the Amazon CloudWatch command line tool, see Command Line Tools.

	Note
	This scenario is for a load-balanced, auto-scaled application. In the following examples, if you aren't using Elastic Load Balancing, omit the list of LoadBalancers from step 2.

API Example

To set up an auto-scaled, load-balanced Amazon EC2 application

Call CreateLaunchConfiguration with the following parameters:
- ImageId = ami-xxxxxxxx
- LaunchConfigurationName = MyLC
- InstanceType = m1.small
Call CreateAutoScalingGroup with the following parameters:
- AutoScalingGroupName = MyAutoScalingGroup
- AvailabilityZones = us-east-1a, us-east-1b
- LaunchConfigurationName = MyLC
- LoadBalancerNames = MyLB
- MaxSize = 20
- MinSize = 2

Call PutScalingPolicy with the following parameters:

AutoScalingGroupName = MyAutoScalingGroup
PolicyName = MyScaleUpPolicy
ScalingAdjustment = 1
AdjustmentType = ChangeInCapacity
Cooldown = 300

	Note
	The `PutScalingPolicy` action will return an ARN that represents your policy. Use your policy ARN, contained in the `PolicyARN` response element, to associate your policy with the CloudWatch alarm that you will create in the following step.

Call PutMetricAlarm from the CloudWatch API with the following parameters:
- AlarmName = MyHighCPUAlarm
- AlarmActions = POLICY-ARN_from_previous_step
- MetricName = CPUUtilization
- Namespace = AWS/EC2
- Statistic = Average
- Period = 600
- EvaluationPeriods = 1
- Threshold = 80
- ComparisonOperator = GreaterThanThreshold
- Dimensions = (Name=AutoScalingGroupName, Value=MyAutoScalingGroup)

Call PutScalingPolicy again with the following parameters:

AutoScalingGroupName = MyAutoScalingGroup
PolicyName = MyScaleDownPolicy
ScalingAdjustment = -1
AdjustmentType = ChangeInCapacity
Cooldown = 300

	Note
	The `PutScalingPolicy` action will return an ARN that represents your scale-down policy. Use your policy ARN, contained in the `PolicyARN` response element, to associate your policy with the CloudWatch alarm that you will create in the following step.

Call PutMetricAlarm from the CloudWatch API with the following parameters:
- AlarmName = MyLowCPUAlarm
- AlarmActions = POLICY-ARN_from_previous_step
- MetricName = CPUUtilization
- Namespace = AWS/EC2
- Statistic = Average
- Period = 600
- EvaluationPeriods = 1
- Threshold = 40
- ComparisonOperator = LessThanThreshold
- Dimensions = (Name=AutoScalingGroupName, Value=MyAutoScalingGroup)

Your Amazon EC2 application has been launched as an auto-scaled and load-balanced application.

Command Line Tools Example

In this example, you will need to enter commands for both Auto Scaling and Amazon CloudWatch.

To set up an auto-scaled, load-balanced Amazon EC2 application

Use the Auto Scaling as-create-launch-config command.

PROMPT>as-create-launch-config MyLC --image-id ami-xxxxxxxx --instance-type m1.small

Auto Scaling returns the following:

OK-Created launch config

Use the Auto Scaling as-create-auto-scaling-group command.

PROMPT>as-create-auto-scaling-group MyAutoScalingGroup --launch-configuration MyLC --availability-zones us-east-1a us-east-1b  --min-size 2 --max-size 20 --load-balancers MyLB

Auto Scaling returns the following:

OK-Created AutoScalingGroup

Use the Auto Scaling as-put-scaling-policy command to create a policy to enlarge your fleet.
```
PROMPT>as-put-scaling-policy MyScaleUpPolicy --auto-scaling-group MyAutoScalingGroup  --adjustment=1 --type ChangeInCapacity  --cooldown 300
```
Auto Scaling returns the following (example output):
```
POLICY-ARN arn:aws:autoscaling:us-east-1:0123456789:scalingPolicy/abc-1234-def-567		
```
Note
The as-put-scaling-policy command returns an ARN that represents your policy. Use your policy ARN to associate your policy with the CloudWatch alarm that you will create in the following step.

Use the CloudWatch mon-put-metric-alarm command, substituting your POLICY-ARN for the --alarm-actions parameter.

PROMPT>mon-put-metric-alarm MyHighCPUAlarm  --comparison-operator  GreaterThanThreshold  --evaluation-periods  1 --metric-name  CPUUtilization  --namespace  "AWS/EC2"  --period  600  --statistic Average --threshold  80 --alarm-actions POLICY-ARN_from_previous_step --dimensions "AutoScalingGroupName=MyAutoScalingGroup"

Amazon CloudWatch returns the following:

OK-Created Alarm

Use the Auto Scaling as-put-scaling-policy command to create a policy to reduce your fleet size. If you are using Windows, wrap the --adjustment parameter in quotation marks: "--adjustment=-1".
```
PROMPT>as-put-scaling-policy MyScaleDownPolicy --auto-scaling-group MyAutoScalingGroup  --adjustment=-1 --type ChangeInCapacity  --cooldown 300
```
Auto Scaling returns the following (example output):
```
POLICY-ARN arn:aws:autoscaling:us-east-1:0123456789:scalingPolicy/abc-1234-def-567		
```
Note
The as-put-scaling-policy command returns an ARN that represents your policy. Use your policy ARN to associate your policy with the CloudWatch alarm that you will create in the following step.

Use the CloudWatch mon-put-metric-alarm command, substituting the MyScaleDownPolicy POLICY-ARN for the ARN shown in the --alarm-actions parameter.

PROMPT>mon-put-metric-alarm MyLowCPUAlarm  --comparison-operator  LessThanThreshold --evaluation-periods  1 --metric-name  CPUUtilization --namespace  "AWS/EC2"  --period  600  --statistic Average --threshold  40  --alarm-actions POLICY-ARN_from_previous_step --dimensions "AutoScalingGroupName=MyAutoScalingGroup"

Amazon CloudWatch returns the following:

OK-Created Alarm

Verify that your Auto Scaling group exists by using the as-describe-auto-scaling-groups command.

PROMPT>as-describe-auto-scaling-groups MyAutoScalingGroup --headers

Auto Scaling returns the following:

AUTO-SCALING-GROUP  GROUP-NAME          LAUNCH-CONFIG  AVAILABILITY-ZONES     LOAD-BALANCERS  MIN-SIZE  MAX-SIZE  DESIRED-CAPACITY
AUTO-SCALING-GROUP  MyAutoScalingGroup  MyLC           us-east-1b,us-east-1a  MyLB            2         20        2
INSTANCE  INSTANCE-ID  AVAILABILITY-ZONE  STATE      STATUS   LAUNCH-CONFIG
INSTANCE  i-xxxxxxxx   us-east-1b         InService  Healthy  MyLC
INSTANCE  i-xxxxxxxx   us-east-1a         InService  Healthy  MyLC

Your Amazon EC2 application has been launched as an auto-scaled and load-balanced application.

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	Note
	The `as-put-scaling-policy` command returns an ARN that represents your policy. Use your policy ARN to associate your policy with the CloudWatch alarm that you will create in the following step.