UpdateReplacePolicy attribute

Use the UpdateReplacePolicy attribute to retain or, in some cases, backup the existing physical instance of a resource when it's replaced during a stack update operation.

When you initiate a stack update, AWS CloudFormation updates resources based on differences between what you submit and the stack's current template and parameters. If you update a resource property that requires that the resource be replaced, CloudFormation recreates the resource during the update. For more information, see Update behaviors of stack resources in the AWS CloudFormation User Guide.

Recreating the resource generates a new physical ID. CloudFormation creates the replacement resource first, and then changes references from other dependent resources to point to the replacement resource. By default, CloudFormation then deletes the old resource. Using the UpdateReplacePolicy, you can specify that CloudFormation retain or, in some cases, create a snapshot of the old resource.

For resources that support snapshots, such as AWS::EC2::Volume, specify Snapshot to have CloudFormation create a snapshot before deleting the old resource instance.

You can apply the UpdateReplacePolicy attribute to any resource. UpdateReplacePolicy is only executed if you update a resource property whose update behavior is specified as Replacement, thereby causing CloudFormation to replace the old resource with a new one with a new physical ID. For example, if you update the Engine property of an AWS::RDS::DBInstance resource type, CloudFormation creates a new resource and replaces the current DB instance resource with the new one. The UpdateReplacePolicy attribute would then dictate whether CloudFormation deleted, retained, or created a snapshot of the old DB instance. The update behavior for each property of a resource is specified in the reference topic for that resource in the AWS resource and property types reference.

The UpdateReplacePolicy attribute applies to stack updates you perform directly, in addition to stack updates performed using change sets.

UpdateReplacePolicy differs from the DeletionPolicy attribute in that it only applies to resources replaced during stack updates. Use DeletionPolicy for resources deleted when a stack is deleted, or when the resource definition itself is deleted from the template as part of a stack update.

The following snippet contains an Amazon RDS database instance resource with a Retain policy for replacement. When this resource is replaced with a new resource with a new physical ID, CloudFormation leaves the old database instance without deleting it.

{
  "AWSTemplateFormatVersion" : "2010-09-09",
  "Resources" : {
    "myDB" : {
      "Type" : "AWS::RDS::DBInstance",
      "DeletionPolicy" : "Retain",
      "UpdateReplacePolicy" : "Retain",
      "Properties" : {}
    }
  }
}

AWSTemplateFormatVersion: 2010-09-09
Resources:
  myDB:
    Type: 'AWS::RDS::DBInstance'
    DeletionPolicy: Retain
    UpdateReplacePolicy: Retain
    Properties: {} 

UpdateReplacePolicy options