Verifying a scaling activity for an Auto Scaling group - Amazon EC2 Auto Scaling

Verifying a scaling activity for an Auto Scaling group

After you create a scaling policy, Amazon EC2 Auto Scaling starts evaluating the policy against the metric. The metric alarm goes to ALARM state when the metric breaches the threshold for a specified number of evaluation periods. This means that a scaling policy could trigger a scaling action soon after it's created. After Amazon EC2 Auto Scaling changes capacity in response to a scaling policy, you can verify the scaling activity in your account. If you want to receive email notification from Amazon EC2 Auto Scaling informing you that a scaling action was triggered, follow the instructions in Getting Amazon SNS notifications when your Auto Scaling group scales.

To view the scaling activities for your Auto Scaling group (console)

  1. Open the Amazon EC2 console at

  2. On the navigation pane, under AUTO SCALING, choose Auto Scaling Groups.

  3. Search for the name of the Auto Scaling group.

    The Instances column shows the number of instances currently running. While an instance is being launched or terminated, the Status column displays a status of "Updating capacity." Wait for a few minutes, and then refresh the view to see the latest status. After a scaling activity completes, notice that the Instances and Desired capacity columns show new values.


    If you're using instance weighting, the Weighted capacity column measures the number of capacity units that the group contains. If this column is hidden, choose the gear-shaped icon in the top-right corner of the section and then enable Weighted capacity.

  4. Select the check box next to the Auto Scaling group.

    A split pane opens up in the bottom part of the Auto Scaling groups page, showing information about the group that's selected.

    1. On the Activity tab, under Activity history, the Status column shows whether your Auto Scaling group has successfully launched or terminated instances.

    2. On the Instance management tab, under Instances, you can view the status of the instances that are currently running. The Lifecycle column contains the state of your instances. Note that it takes a short time for an instance to launch. After the instance starts, its lifecycle state changes to InService.

To view the scaling activities for your Auto Scaling group (AWS CLI)

Use the following describe-scaling-activities command.

aws autoscaling describe-scaling-activities --auto-scaling-group-name my-asg

The following is example output.

Scaling activities are ordered by start time. Activities still in progress are described first.

{ "Activities": [ { "ActivityId": "5e3a1f47-2309-415c-bfd8-35aa06300799", "AutoScalingGroupName": "my-asg", "Description": "Terminating EC2 instance: i-06c4794c2499af1df", "Cause": "At 2020-02-11T18:34:10Z a monitor alarm TargetTracking-my-asg-AlarmLow-b9376cab-18a7-4385-920c-dfa3f7783f82 in state ALARM triggered policy my-target-tracking-policy changing the desired capacity from 3 to 2. At 2020-02-11T18:34:31Z an instance was taken out of service in response to a difference between desired and actual capacity, shrinking the capacity from 3 to 2. At 2020-02-11T18:34:31Z instance i-06c4794c2499af1df was selected for termination.", "StartTime": "2020-02-11T18:34:31.268Z", "EndTime": "2020-02-11T18:34:53Z", "StatusCode": "Successful", "Progress": 100, "Details": "{\"Subnet ID\":\"subnet-5ea0c127\",\"Availability Zone\":\"us-west-2a\"...}" }, ... ] }

To verify the size of your Auto Scaling group (AWS CLI)

Use the describe-auto-scaling-groups command.

aws autoscaling describe-auto-scaling-groups --auto-scaling-group-name my-asg

The following is example output, with details about the group and the currently running instances.

{ "AutoScalingGroups": [ { "AutoScalingGroupARN": "arn", "ServiceLinkedRoleARN": "arn", "TargetGroupARNs": [], "SuspendedProcesses": [], "LaunchTemplate": { "LaunchTemplateName": "my-launch-template", "Version": "1", "LaunchTemplateId": "lt-050555ad16a3f9c7f" }, "Tags": [], "EnabledMetrics": [], "LoadBalancerNames": [], "AutoScalingGroupName": "my-asg", "DefaultCooldown": 300, "MinSize": 1, "Instances": [ { "ProtectedFromScaleIn": false, "AvailabilityZone": "us-west-2a", "LaunchTemplate": { "LaunchTemplateName": "my-launch-template", "Version": "1", "LaunchTemplateId": "lt-050555ad16a3f9c7f" }, "InstanceId": "i-05b4f7d5be44822a6", "HealthStatus": "Healthy", "LifecycleState": "Pending" }, { "ProtectedFromScaleIn": false, "AvailabilityZone": "us-west-2a", "LaunchTemplate": { "LaunchTemplateName": "my-launch-template", "Version": "1", "LaunchTemplateId": "lt-050555ad16a3f9c7f" }, "InstanceId": "i-0c20ac468fa3049e8", "HealthStatus": "Healthy", "LifecycleState": "InService" } ], "MaxSize": 5, "VPCZoneIdentifier": "subnet-c87f2be0", "HealthCheckGracePeriod": 300, "TerminationPolicies": [ "Default" ], "CreatedTime": "2019-03-18T23:30:42.611Z", "AvailabilityZones": [ "us-west-2a" ], "HealthCheckType": "EC2", "NewInstancesProtectedFromScaleIn": false, "DesiredCapacity": 2 } ] }