Replace Auto Scaling instances based on maximum instance lifetime - Amazon EC2 Auto Scaling
ConsiderationsSet the maximum instance lifetimeLimitations

Replace Auto Scaling instances based on maximum instance lifetime

The maximum instance lifetime specifies the maximum amount of time (in seconds) that an instance can be in service before it is terminated and replaced. A common use case might be a requirement to replace your instances on a schedule because of internal security policies or external compliance controls.

You must specify a value of at least 86,400 seconds (one day). To clear a previously set value, specify a new value of 0. This setting applies to all current and future instances in your Auto Scaling group.

Considerations

The following are considerations when using this feature:

  • Whenever an earlier instance is replaced and a new instance launches, the new instance uses the launch template or launch configuration that is currently associated with the Auto Scaling group. If your launch template or launch configuration specifies the Amazon Machine Image (AMI) ID of a different version of your application, this version of your application will be deployed automatically.

  • Setting the maximum instance lifetime too low can cause instances to be replaced faster than desired. Amazon EC2 Auto Scaling will usually replace instances one at a time, with a pause between replacements. However, if the specified maximum instance lifetime doesn't provide enough time to replace each instance individually, Amazon EC2 Auto Scaling must replace more than one instance at a time. Several instances might be replaced at once, by up to 10 percent of the current capacity of your Auto Scaling group. To avoid replacing too many instances at once, either set a longer maximum instance lifetime or use instance scale-in protection to temporarily prevent individual instances from being terminated. For more information, see Use instance scale-in protection to control instance termination.

  • By default, Amazon EC2 Auto Scaling creates a new scaling activity for terminating the instance and then terminates it. While the instance is terminating, another scaling activity launches a new instance. You can change this behavior to launch before terminating by using an instance maintenance policy. For more information, see Instance maintenance policies.

Set the maximum instance lifetime

When you create an Auto Scaling group in the console, you cannot set the maximum instance lifetime. However, after the group is created, you can edit it to set the maximum instance lifetime.

To set the maximum instance lifetime for a 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 at the bottom of the Auto Scaling groups page, showing information about the group you selected.

  3. On the Details tab, choose Advanced configurations, Edit.

  4. For Maximum instance lifetime, enter the maximum number of seconds that an instance can be in service.

  5. Choose Update.

On the Activity tab, under Activity history, you can view the replacement of instances in the group throughout its history.

To set the maximum instance lifetime for a group (AWS CLI)

You can also use the AWS CLI to set the maximum instance lifetime for new or existing Auto Scaling groups.

For new Auto Scaling groups, use the create-auto-scaling-group command.

aws autoscaling create-auto-scaling-group --cli-input-json file://~/config.json

The following is an example config.json file that shows a maximum instance lifetime of 2592000 seconds (30 days).

{
    "AutoScalingGroupName": "my-asg",
    "LaunchTemplate": {
        "LaunchTemplateName": "my-launch-template",
        "Version": "$Default"
    },
    "MinSize": 1,
    "MaxSize": 5,
    "MaxInstanceLifetime": 2592000,
    "VPCZoneIdentifier": "subnet-5ea0c127,subnet-6194ea3b,subnet-c934b782",
    "Tags": []
}

For existing Auto Scaling groups, use the update-auto-scaling-group command.

aws autoscaling update-auto-scaling-group --auto-scaling-group-name my-existing-asg --max-instance-lifetime 2592000
To verify the maximum instance lifetime for an Auto Scaling group

Use the describe-auto-scaling-groups command.

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

Limitations

  • Maximum lifetime not guaranteed to be exact for every instance: Instances are not guaranteed to be replaced only at the end of their maximum duration. In some situations, Amazon EC2 Auto Scaling might need to start replacing instances immediately after you update the maximum instance lifetime parameter. The reason for this behavior is to avoid replacing all instances at the same time.

  • Instance scale-in protection honored: Amazon EC2 Auto Scaling provides instance scale-in protection to help you control which instances it can terminate. When this protection is enabled on an instance, Amazon EC2 Auto Scaling will not terminate the instance even if it has reached its maximum instance lifetime.

  • Instances terminated before launch: When there is only one instance in the Auto Scaling group, the maximum instance lifetime feature can result in an outage because Amazon EC2 Auto Scaling terminates an instance and then launches a new instance by default. To change this behavior to launch before terminating, see Instance maintenance policies.