# RefreshPreferences
Describes the preferences for an instance refresh.
## Contents
** AlarmSpecification **
(Optional) The CloudWatch alarm specification. CloudWatch alarms can be used to identify any issues and fail the operation if an alarm threshold is met.
Type: [AlarmSpecification](API_AlarmSpecification.md) object
Required: No
** AutoRollback **
(Optional) Indicates whether to roll back the Auto Scaling group to its previous configuration if the instance refresh fails or a CloudWatch alarm threshold is met. The default is `false`.
A rollback is not supported in the following situations:
+ There is no desired configuration specified for the instance refresh.
+ The Auto Scaling group has a launch template that uses an AWS Systems Manager parameter instead of an AMI ID for the `ImageId` property.
+ The Auto Scaling group uses the launch template's `$Latest` or `$Default` version.
For more information, see [Undo changes with a rollback](https://docs.aws.amazon.com/autoscaling/ec2/userguide/instance-refresh-rollback.html) in the *Amazon EC2 Auto Scaling User Guide*.
Type: Boolean
Required: No
** BakeTime **
The amount of time, in seconds, to wait at the end of an instance refresh before the instance refresh is considered complete.
Type: Integer
Valid Range: Minimum value of 0. Maximum value of 172800.
Required: No
** CheckpointDelay **
(Optional) The amount of time, in seconds, to wait after a checkpoint before continuing. This property is optional, but if you specify a value for it, you must also specify a value for `CheckpointPercentages`. If you specify a value for `CheckpointPercentages` and not for `CheckpointDelay`, the `CheckpointDelay` defaults to `3600` (1 hour).
Type: Integer
Valid Range: Minimum value of 0. Maximum value of 172800.
Required: No
** CheckpointPercentages.member.N **
(Optional) Threshold values for each checkpoint in ascending order. Each number must be unique. To replace all instances in the Auto Scaling group, the last number in the array must be `100`.
For usage examples, see [Add checkpoints to an instance refresh](https://docs.aws.amazon.com/autoscaling/ec2/userguide/asg-adding-checkpoints-instance-refresh.html) in the *Amazon EC2 Auto Scaling User Guide*.
Type: Array of integers
Valid Range: Minimum value of 1. Maximum value of 100.
Required: No
** InstanceWarmup **
A time period, in seconds, during which an instance refresh waits before moving on to replacing the next instance after a new instance enters the `InService` state.
This property is not required for normal usage. Instead, use the `DefaultInstanceWarmup` property of the Auto Scaling group. The `InstanceWarmup` and `DefaultInstanceWarmup` properties work the same way. Only specify this property if you must override the `DefaultInstanceWarmup` property.
If you do not specify this property, the instance warmup by default is the value of the `DefaultInstanceWarmup` property, if defined (which is recommended in all cases), or the `HealthCheckGracePeriod` property otherwise.
Type: Integer
Valid Range: Minimum value of 0.
Required: No
** MaxHealthyPercentage **
Specifies the maximum percentage of the group that can be in service and healthy, or pending, to support your workload when replacing instances. The value is expressed as a percentage of the desired capacity of the Auto Scaling group. Value range is 100 to 200.
If you specify `MaxHealthyPercentage`, you must also specify `MinHealthyPercentage`, and the difference between them cannot be greater than 100. A larger range increases the number of instances that can be replaced at the same time.
If you do not specify this property, the default is 100 percent, or the percentage set in the instance maintenance policy for the Auto Scaling group, if defined.
Type: Integer
Valid Range: Minimum value of 100. Maximum value of 200.
Required: No
** MinHealthyPercentage **
Specifies the minimum percentage of the group to keep in service, healthy, and ready to use to support your workload to allow the operation to continue. The value is expressed as a percentage of the desired capacity of the Auto Scaling group. Value range is 0 to 100.
If you do not specify this property, the default is 90 percent, or the percentage set in the instance maintenance policy for the Auto Scaling group, if defined.
Type: Integer
Valid Range: Minimum value of 0. Maximum value of 100.
Required: No
** ScaleInProtectedInstances **
Choose the behavior that you want Amazon EC2 Auto Scaling to use if instances protected from scale in are found.
The following lists the valid values:
Refresh
Amazon EC2 Auto Scaling replaces instances that are protected from scale in.
Ignore
Amazon EC2 Auto Scaling ignores instances that are protected from scale in and continues to replace instances that are not protected.
Wait (default)
Amazon EC2 Auto Scaling waits one hour for you to remove scale-in protection. Otherwise, the instance refresh will fail.
Type: String
Valid Values: `Refresh | Ignore | Wait`
Required: No
** SkipMatching **
(Optional) Indicates whether skip matching is enabled. If enabled (`true`), then Amazon EC2 Auto Scaling skips replacing instances that match the desired configuration. If no desired configuration is specified, then it skips replacing instances that have the same launch template and instance types that the Auto Scaling group was using before the start of the instance refresh. The default is `false`.
For more information, see [Use an instance refresh with skip matching](https://docs.aws.amazon.com/autoscaling/ec2/userguide/asg-instance-refresh-skip-matching.html) in the *Amazon EC2 Auto Scaling User Guide*.
Type: Boolean
Required: No
** StandbyInstances **
Choose the behavior that you want Amazon EC2 Auto Scaling to use if instances in `Standby` state are found.
The following lists the valid values:
Terminate
Amazon EC2 Auto Scaling terminates instances that are in `Standby`.
Ignore
Amazon EC2 Auto Scaling ignores instances that are in `Standby` and continues to replace instances that are in the `InService` state.
Wait (default)
Amazon EC2 Auto Scaling waits one hour for you to return the instances to service. Otherwise, the instance refresh will fail.
Type: String
Valid Values: `Terminate | Ignore | Wait`
Required: No
## See Also
For more information about using this API in one of the language-specific AWS SDKs, see the following:
+ [AWS SDK for C\$1\$1](https://docs.aws.amazon.com/goto/SdkForCpp/autoscaling-2011-01-01/RefreshPreferences)
+ [AWS SDK for Java V2](https://docs.aws.amazon.com/goto/SdkForJavaV2/autoscaling-2011-01-01/RefreshPreferences)
+ [AWS SDK for Ruby V3](https://docs.aws.amazon.com/goto/SdkForRubyV3/autoscaling-2011-01-01/RefreshPreferences)