Verify a scaling activity for an Auto Scaling
group

In the Amazon EC2 Auto Scaling section of the Amazon EC2 console, the Activity
history for an Auto Scaling group lets you view the current status of a
scaling activity that is currently in progress. When the scaling activity is
finished, you can see whether it succeeds or not. This is particularly useful when
you are creating Auto Scaling groups or you are adding scaling conditions to existing
groups.

When you add a target tracking, step, or simple scaling policy to your Auto Scaling group,
Amazon EC2 Auto Scaling immediately 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 result in a
scaling activity soon after it’s created. After Amazon EC2 Auto Scaling adjusts the desired
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
about a scaling activity, follow the instructions in Get Amazon SNS notifications when your Auto Scaling group
scales.

Tip

In the following procedure, you look at the Activity
history and Instances sections for the Auto Scaling
group. In both, the named columns should already be displayed. To display hidden
columns or change the number of rows shown, choose the gear icon on the top
right corner of each section to open the preferences modal, update the settings
as needed, and choose Confirm.

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

1. Open the Amazon EC2 console at
   https://console.aws.amazon.com/ec2/, and choose Auto Scaling Groups from the navigation pane.

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

   A split pane opens up in the bottom of the Auto Scaling
   groups page.

3. On the Activity tab, under Activity
   history, the Status column shows whether
   your Auto Scaling group has successfully launched or terminated instances, or
   whether the scaling activity is still in progress.

4. (Optional) If you have a lot of scaling activities, you can choose the
   > icon at the top edge of the activity history to see
   the next page of scaling activities.

5. On the Instance management tab, under
   Instances, the Lifecycle
   column contains the state of your instances. After the instance starts and
   any lifecycle hooks have finished, its lifecycle state changes to
   InService. The Health status column
   shows the result of the EC2 instance health check on your instance.

To view the scaling activities for an 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\"...}",
      "AutoScalingGroupARN": "arn:aws:autoscaling:us-west-2:123456789012:autoScalingGroup:283179a2-f3ce-423d-93f6-66bb518232f7:autoScalingGroupName/my-asg"
    },
...
  ]
}

For a description of the fields in the output, see Activity in the
Amazon EC2 Auto Scaling API Reference.

For help retrieving the scaling activities for a deleted group and for information
about the types of errors that you may encounter and how to handle them, see Troubleshoot Amazon EC2 Auto Scaling.