How the standby state works Health status of an instance in a standby state Temporarily remove an instance (console)Temporarily remove an instance (AWS CLI)

Temporarily remove instances from your Auto Scaling group

You can put an instance that is in the InService state into the Standby state, update or troubleshoot the instance, and then return the instance to service. Instances that are on standby are still part of the Auto Scaling group, but they do not actively handle load balancer traffic.

This feature helps you stop and start the instances or reboot them without worrying about Amazon EC2 Auto Scaling terminating the instances as part of its health checks or during scale-in events.

For example, you can change the Amazon Machine Image (AMI) for an Auto Scaling group at any time by changing the launch template or launch configuration. Any subsequent instances that the Auto Scaling group launches use this AMI. However, the Auto Scaling group does not update the instances that are currently in service. You can terminate these instances and let Amazon EC2 Auto Scaling replace them, or use the instance refresh feature to terminate and replace the instances. Or, you can put the instances on standby, update the software, and then put the instances back in service.

Detaching instances from an Auto Scaling group is similar to putting instances on standby. Detaching instances might be useful if you want to manage the instances like standalone EC2 instances and possibly terminate them. For more information, see Detach EC2 instances from your Auto Scaling group.

Important

When you put instances on standby, your Auto Scaling group can become unbalanced between Availability Zones. Amazon EC2 Auto Scaling compensates by rebalancing the Availability Zones unless you suspend the AZRebalance process. For more information, see Suspend and resume a process for an Auto Scaling group.

Contents

How the standby state works
Health status of an instance in a standby state
Temporarily remove an instance (console)
Temporarily remove an instance (AWS CLI)

Important

You are billed for instances that are in a standby state.

How the standby state works

The standby state works as follows to help you temporarily remove an instance from your Auto Scaling group:

You put the instance into the standby state. The instance remains in this state until you exit the standby state.
If there is a load balancer target group or Classic Load Balancer attached to your Auto Scaling group, the instance is deregistered from the load balancer. If connection draining is enabled for the load balancer, Elastic Load Balancing waits 300 seconds by default before completing the deregistration process, which helps in-flight requests to complete.
By default, the value that you specified as your desired capacity is decremented when you put an instance on standby. This prevents the launch of an additional instance while you have this instance on standby. Alternatively, you can specify that your desired capacity is not decremented. If you specify this option, the Auto Scaling group launches an instance to replace the one on standby. The intention is to help you maintain capacity for your application while one or more instances are on standby.
You can update or troubleshoot the instance.
You return the instance to service by exiting the standby state.
After you put an instance that was on standby back in service, the desired capacity is incremented. If you did not decrement the capacity when you put the instance on standby, the Auto Scaling group detects that you have more instances than you need. It applies the termination policy in effect to reduce the size of the group. For more information, see Control which Auto Scaling instances terminate during scale in.
If there is a load balancer target group or Classic Load Balancer attached to your Auto Scaling group, the instance is registered with the load balancer.

The following illustration shows the transitions between instance states in this process:

Instances enter and exit the standby state.

For more information about the complete lifecycle of instances in an Auto Scaling group, see Amazon EC2 Auto Scaling instance lifecycle.

Health status of an instance in a standby state

Amazon EC2 Auto Scaling does not perform health checks on instances that are in a standby state. While the instance is in a standby state, its health status reflects the status that it had before you put it on standby. Amazon EC2 Auto Scaling does not perform a health check on the instance until you put it back in service.

For example, if you put a healthy instance on standby and then terminate it, Amazon EC2 Auto Scaling continues to report the instance as healthy. If you attempt to put a terminated instance that was on standby back in service, Amazon EC2 Auto Scaling performs a health check on the instance, determines that it is terminating and unhealthy, and launches a replacement instance. For an introduction to health checks, see Health checks for Auto Scaling instances.

Temporarily remove an instance (console)

The following procedure demonstrates the general process for updating an instance that is currently in service.

To temporarily remove an instance

Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/, and choose Auto Scaling Groups from the navigation pane.
Select the check box next to the Auto Scaling group.

A split pane opens up in the bottom of the Auto Scaling groups page.
On the Instance management tab, in Instances, select an instance.
Choose Actions, Set to Standby.
In the Set to Standby dialog box, select the check box to launch a replacement instance. Leave it unchecked to decrement the desired capacity. Choose Set to Standby.
You can update or troubleshoot your instance as needed. When you have finished, continue with the next step to return the instance to service.
Select the instance, choose Actions, Set to InService. In the Set to InService dialog box, choose Set to InService.

Temporarily remove an instance (AWS CLI)

The following procedure demonstrates the general process for updating an instance that is currently in service.

To temporarily remove an instance

Use the following describe-auto-scaling-instances command to identify the instance to update.


aws autoscaling describe-auto-scaling-instances

The following is an example response.


{
    "AutoScalingInstances": [
        {
            "ProtectedFromScaleIn": false,
            "AvailabilityZone": "us-west-2a",
            "LaunchTemplate": {
                "LaunchTemplateName": "my-launch-template",
                "Version": "1",
                "LaunchTemplateId": "lt-050555ad16a3f9c7f"
            },
            "InstanceId": "i-05b4f7d5be44822a6",
            "AutoScalingGroupName": "my-asg",
            "HealthStatus": "HEALTHY",
            "LifecycleState": "InService"
        },
       ...
    ]
}

Move the instance into a Standby state using the following enter-standby command. The --should-decrement-desired-capacity option decreases the desired capacity so that the Auto Scaling group does not launch a replacement instance.


aws autoscaling enter-standby --instance-ids i-05b4f7d5be44822a6 \
  --auto-scaling-group-name my-asg --should-decrement-desired-capacity

The following is an example response.


{
    "Activities": [
        {
            "Description": "Moving EC2 instance to Standby: i-05b4f7d5be44822a6",
            "AutoScalingGroupName": "my-asg",
            "ActivityId": "3b1839fe-24b0-40d9-80ae-bcd883c2be32",
            "Details": "{\"Availability Zone\":\"us-west-2a\"}",
            "StartTime": "2014-12-15T21:31:26.150Z",
            "Progress": 50,
            "Cause": "At 2014-12-15T21:31:26Z instance i-05b4f7d5be44822a6 was moved to standby 
              in response to a user request, shrinking the capacity from 4 to 3.",
            "StatusCode": "InProgress"
        }
    ]
}

(Optional) Verify that the instance is in Standby using the following describe-auto-scaling-instances command.


aws autoscaling describe-auto-scaling-instances --instance-ids i-05b4f7d5be44822a6

The following is an example response. Notice that the status of the instance is now Standby.


{
    "AutoScalingInstances": [
        {
            "ProtectedFromScaleIn": false,
            "AvailabilityZone": "us-west-2a",
            "LaunchTemplate": {
                "LaunchTemplateName": "my-launch-template",
                "Version": "1",
                "LaunchTemplateId": "lt-050555ad16a3f9c7f"
            },
            "InstanceId": "i-05b4f7d5be44822a6",
            "AutoScalingGroupName": "my-asg",
            "HealthStatus": "HEALTHY",
            "LifecycleState": "Standby"
        },
       ...
    ]
}

You can update or troubleshoot your instance as needed. When you have finished, continue with the next step to return the instance to service.

Put the instance back in service using the following exit-standby command.


aws autoscaling exit-standby --instance-ids i-05b4f7d5be44822a6 --auto-scaling-group-name my-asg

The following is an example response.


{
    "Activities": [
        {
            "Description": "Moving EC2 instance out of Standby: i-05b4f7d5be44822a6",
            "AutoScalingGroupName": "my-asg",
            "ActivityId": "db12b166-cdcc-4c54-8aac-08c5935f8389",
            "Details": "{\"Availability Zone\":\"us-west-2a\"}",
            "StartTime": "2014-12-15T21:46:14.678Z",
            "Progress": 30,
            "Cause": "At 2014-12-15T21:46:14Z instance i-05b4f7d5be44822a6 was moved out of standby in
               response to a user request, increasing the capacity from 3 to 4.",
            "StatusCode": "PreInService"
        }
    ]
}

(Optional) Verify that the instance is back in service using the following describe-auto-scaling-instances command.


aws autoscaling describe-auto-scaling-instances --instance-ids i-05b4f7d5be44822a6

The following is an example response. Notice that the status of the instance is InService.


{
    "AutoScalingInstances": [
        {
            "ProtectedFromScaleIn": false,
            "AvailabilityZone": "us-west-2a",
            "LaunchTemplate": {
                "LaunchTemplateName": "my-launch-template",
                "Version": "1",
                "LaunchTemplateId": "lt-050555ad16a3f9c7f"
            },
            "InstanceId": "i-05b4f7d5be44822a6",
            "AutoScalingGroupName": "my-asg",
            "HealthStatus": "HEALTHY",
            "LifecycleState": "InService"
        },
       ...
    ]
}

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Document Conventions

Use instance scale-in protection

Suspend-resume processes