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Auto Scaling
User Guide

Manual Scaling

At any time, you can change the size of an existing Auto Scaling group by updating the desired capacity of the Auto Scaling group, or by updating the instances that are attached to the Auto Scaling group.

Change the Size of Your Auto Scaling Group Using the Console

When you change the size of your Auto Scaling group, Auto Scaling manages the process of launching or terminating instances to maintain the new group size.

The following example assumes that you've created an Auto Scaling group with a minimum size of 1 and a maximum size of 5. Therefore, the group currently has one running instance.

To change the size of your Auto Scaling group

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

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

  3. Select your Auto Scaling group.

  4. On the Details tab, choose Edit.

  5. For Desired, increase the desired capacity by one. For example, if the current value is 1, type 2.

    The desired capacity must be less than or equal to the maximum size of the group. Therefore, you must update Max if your new value for Desired is greater than Max.

    When you are finished, choose Save.

Now, verify that your Auto Scaling group has launched one additional instance.

To verify that the size of your Auto Scaling group has changed

  1. On the Activity History tab, the Status column shows the current status of your instance. You can use the refresh button until you see the status of your instance change to Successful, indicating that your Auto Scaling group has successfully launched a new instance.

  2. On the Instances tab, the Lifecycle column shows the state of your instances. It takes a short time for an instance to launch. After the instance starts, its state changes to InService. You can see that your Auto Scaling group has launched 1 new instance, and it is in the InService state.

Change the Size of Your Auto Scaling Group Using the AWS CLI

When you change the size of your Auto Scaling group, Auto Scaling manages the process of launching or terminating instances to maintain the new group size.

The following example assumes that you've created an Auto Scaling group with a minimum size of 1 and a maximum size of 5. Therefore, the group currently has one running instance.

Use the set-desired-capacity command to change the size of your Auto Scaling group, as shown in the following example:

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aws autoscaling set-desired-capacity --auto-scaling-group-name my-asg --desired-capacity 2

By default, the command does not wait for the cooldown period specified for the group to complete. You can override the default behavior and wait for the cooldown period to complete by specifying the –-honor-cooldown option as shown in the following example. For more information, see Auto Scaling Cooldowns.

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aws autoscaling set-desired-capacity --auto-scaling-group-name my-asg --desired-capacity 2 --honor-cooldown

Use the describe-auto-scaling-groups command to confirm that the size of your Auto Scaling group has changed, as in the following example:

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

Auto Scaling responds with details about the group and instances launched. The response should be similar to the following example:

{
    "AutoScalingGroups": [
        {
            "AutoScalingGroupARN": "arn",
            "HealthCheckGracePeriod": 300,
            "SuspendedProcesses": [],
            "DesiredCapacity": 2,
            "Tags": [],
            "EnabledMetrics": [],
            "LoadBalancerNames": [],
            "AutoScalingGroupName": "my-asg",
            "DefaultCooldown": 300,
            "MinSize": 1,
            "Instances": [
                {
                    "InstanceId": "i-33388a3f",
                    "AvailabilityZone": "us-west-2a",
                    "HealthStatus": "Healthy",
                    "LifecycleState": "InService",
                    "LaunchConfigurationName": "my-lc"
                }
            ],
            "MaxSize": 5,
            "VPCZoneIdentifier": "subnet-e4f33493",
            "TerminationPolicies": [
                "Default"
            ],
            "LaunchConfigurationName": "my-lc",
            "CreatedTime": "2014-12-12T23:30:42.611Z",
            "AvailabilityZones": [
                "us-west-2a"
            ],
            "HealthCheckType": "EC2"
        }
    ]
}

Notice that DesiredCapacity shows the new value. Your Auto Scaling group has launched an additional instance.