Manual scaling for Amazon EC2 Auto Scaling

At any time, you can change the size of an existing Auto Scaling group manually. You can
either update the desired capacity of the Auto Scaling group, or update the instances that are
attached to the Auto Scaling group. Manually scaling your group can be useful when automatic
scaling is not needed or when you need to hold capacity at a fixed number of
instances.

Change the size of your Auto Scaling group
(console)

When you change the desired capacity of your Auto Scaling group, Amazon EC2 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/, and choose Auto Scaling Groups from the navigation pane.

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

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

3. On the Details tab, choose Group
   details, Edit.

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

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

5. When you are finished, choose Update.

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 tab, in Activity
   history, the Status column shows the
   current status of your instance. Use the refresh button until you see the
   status of your instance change to Successful. This
   indicates that your Auto Scaling group has successfully launched a new instance.

   Note

   If the instance fails to launch, you can find troubleshooting tips in
   Troubleshoot Amazon EC2 Auto Scaling.

2. On the Instance management tab, in
   Instances, 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
(AWS CLI)

When you change the size of your Auto Scaling group, Amazon EC2 Auto Scaling manages the process of
launching or terminating instances to maintain the new group size. The default
behavior is not to wait for the default cooldown period to complete, but you can
override the default and wait for the cooldown period to complete. For more
information, see Scaling cooldowns for
Amazon EC2 Auto Scaling.

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

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

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

If you choose to honor the default cooldown period for your Auto Scaling group, you must
specify the –-honor-cooldown option as shown in the following
example.

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

To verify the size of your Auto Scaling group

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

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

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

{
    "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",
                    "InstanceType": "t2.micro",
                    "HealthStatus": "Healthy",
                    "LifecycleState": "Pending"
                },
                
{
                    "ProtectedFromScaleIn": false,
                    "AvailabilityZone": "us-west-2a",
                    "LaunchTemplate": 
{
                        "LaunchTemplateName": "my-launch-template",
                        "Version": "1",
                        "LaunchTemplateId": "lt-050555ad16a3f9c7f"
                    },
                    "InstanceId": "i-0c20ac468fa3049e8",
                    "InstanceType": "t2.micro",
                    "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
        }
    ]
}

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