Nesting an existing stack - AWS CloudFormation
Nested stack import validationNest an existing stack using the AWS Management ConsoleNest an existing stack using the AWS CLI

Nesting an existing stack

Use the resource import feature to nest an existing stack within another existing stack. Nested stacks are common components that you declare and reference from within other templates. That way, you can avoid copying and pasting the same configurations into your templates and simplify stack updates. If you have a template for a common component, you can use the AWS::CloudFormation::Stack resource to reference this template from within another template. For more information on nested stacks, see Working with nested stacks.

AWS CloudFormation only supports one level of nesting using resource import. This means that you can't import a stack into a child stack or import a stack that has children.

If you're new to importing, we recommend that you first review the introductory information in the Bringing existing resources into CloudFormation management topic.

Nested stack import validation

During a nested stack import operation, AWS CloudFormation performs the following validations.

  • The nested AWS::CloudFormation::Stack definition in the parent stack template matches the actual nested stack's template.

  • The tags for the nested AWS::CloudFormation::Stack definition in the parent stack template match the tags for the actual nested stack resource.

Nest an existing stack using the AWS Management Console

  1. Add the AWS::CloudFormation::Stack resource to the parent stack template with a Retain DeletionPolicy. In the following example parent template, NestedStack is the target of the import.

    JSON

    {
  "AWSTemplateFormatVersion" : "2010-09-09",
  "Resources" : {
    "ServiceTable":{
           "Type":"AWS::DynamoDB::Table",
           "Properties":{
              "TableName":"Service",
              "AttributeDefinitions":[
                 {
                    "AttributeName":"key",
                    "AttributeType":"S"
                 }
              ],
              "KeySchema":[
                 {
                    "AttributeName":"key",
                    "KeyType":"HASH"
                 }
              ],
              "ProvisionedThroughput":{
                 "ReadCapacityUnits":5,
                 "WriteCapacityUnits":1
              }
           }
        },
    "NestedStack" : {
      "Type" : "AWS::CloudFormation::Stack",
      "DeletionPolicy": "Retain",
      "Properties" : {
      "TemplateURL" : "https://s3.amazonaws.com/cloudformation-templates-us-east-2/EC2ChooseAMI.template",
        "Parameters" : {
          "InstanceType" : "t1.micro",
          "KeyName" : "mykey"
        }
      }
    }
  }
}

    YAML

    AWSTemplateFormatVersion: 2010-09-09
Resources:
  ServiceTable:
    Type: 'AWS::DynamoDB::Table'
    Properties:
      TableName: Service
      AttributeDefinitions:
        - AttributeName: key
          AttributeType: S
      KeySchema:
        - AttributeName: key
          KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits: 5
        WriteCapacityUnits: 1
  NestedStack:
    Type: 'AWS::CloudFormation::Stack'
    DeletionPolicy: Retain
    Properties:
      TemplateURL: >-
        https://s3.amazonaws.com/cloudformation-templates-us-east-2/EC2ChooseAMI.template
      Parameters:
        InstanceType: t1.micro
        KeyName: mykey

  2. Open the AWS CloudFormation console.

  3. On the Stacks page, with the parent stack selected, choose Stack actions, and then choose Import resources into stack.

    The Import resources into stack option in the console.

  4. Read the Import overview page for a list of things you're required to provide during this operation. Then, choose Next.

  5. On the Specify template page, provide the updated parent template using one of the following methods, and then choose Next.

    • Choose Amazon S3 URL, and then specify the URL for your template in the text box.

    • Choose Upload a template file, and then browse for your template.

  6. On the Identify resources page, identify the AWS::CloudFormation::Stack resource.

    1. Under Identifier property, choose the type of resource identifier. For example, an AWS::CloudFormation::Stack resource can be identified using the StackId property.

    2. Under Identifier value, type the ARN of the stack you're importing. For example, arn:aws:cloudformation:us-west-2:12345678910:stack/mystack/5b918d10-cd98-11ea-90d5-0a9cd3354c10.

      The Identify resources page in the console.

    3. Choose Next.

  7. On the Specify stack details page, modify any parameters, and then choose Next. This automatically creates a change set.

    Important

    The import operation fails if you modify existing parameters that initiate a create, update, or delete operation.

  8. On the Review TargetParentStackName page, confirm that the correct resource is being imported, and then choose Import resources. This automatically executes the change set created in the last step. Any stack-level tags are applied to imported resources at this time.

  9. The Events pane of the Stack details page for your parent stack displays.

    The Events tab in the console.
    Note

    It's not necessary to run drift detection on the parent stack after this import operation because the AWS::CloudFormation::Stack resource was already managed by AWS CloudFormation.

Nest an existing stack using the AWS CLI

  1. Add the AWS::CloudFormation::Stack resource to the parent stack template with a Retain DeletionPolicy. In the following example parent template, NestedStack is the target of the import.

    JSON

    {
  "AWSTemplateFormatVersion" : "2010-09-09",
  "Resources" : {
    "ServiceTable":{
           "Type":"AWS::DynamoDB::Table",
           "Properties":{
              "TableName":"Service",
              "AttributeDefinitions":[
                 {
                    "AttributeName":"key",
                    "AttributeType":"S"
                 }
              ],
              "KeySchema":[
                 {
                    "AttributeName":"key",
                    "KeyType":"HASH"
                 }
              ],
              "ProvisionedThroughput":{
                 "ReadCapacityUnits":5,
                 "WriteCapacityUnits":1
              }
           }
        },
    "NestedStack" : {
      "Type" : "AWS::CloudFormation::Stack",
      "DeletionPolicy": "Retain",
      "Properties" : {
      "TemplateURL" : "https://s3.amazonaws.com/cloudformation-templates-us-east-2/EC2ChooseAMI.template",
        "Parameters" : {
          "InstanceType" : "t1.micro",
          "KeyName" : "mykey"
        }
      }
    }
  }
}

    YAML

    AWSTemplateFormatVersion: 2010-09-09
Resources:
  ServiceTable:
    Type: 'AWS::DynamoDB::Table'
    Properties:
      TableName: Service
      AttributeDefinitions:
        - AttributeName: key
          AttributeType: S
      KeySchema:
        - AttributeName: key
          KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits: 5
        WriteCapacityUnits: 1
  NestedStack:
    Type: 'AWS::CloudFormation::Stack'
    DeletionPolicy: Retain
    Properties:
      TemplateURL: >-
        https://s3.amazonaws.com/cloudformation-templates-us-east-2/EC2ChooseAMI.template
      Parameters:
        InstanceType: t1.micro
        KeyName: mykey

  2. Compose a JSON string as shown in the following example, with these modifications:

    • Replace NestedStack with the logical ID of the target resource as specified in the template.

    • Replace arn:aws:cloudformation:us-west-2:12345678910:stack/mystack/5b918d10-cd98-11ea-90d5-0a9cd3354c10 with the ARN of the stack you want to import.

    [{\"ResourceType\":\AWS::CloudFormation::Stack\",\"LogicalResourceId\":\"NestedStack\",\"ResourceIdentifier\":{\"StackId\":\"arn:aws:cloudformation:us-east-2:123456789012:stack/mystack-mynestedstack-sggfrhxhum7w/f449b250-b969-11e0-a185-5081d0136786\"}}]

    Alternatively, you can specify the parameters in a configuration file.

    For example, to import NestedStack, you might create a ResourcesToImport.txt file that contains the following configuration.

    JSON

    [
  {
      "ResourceType":"AWS::CloudFormation::Stack",
      "LogicalResourceId":"NestedStack",
      "ResourceIdentifier": {
        "StackId":"arn:aws:cloudformation:us-west-2:12345678910:stack/mystack/5b918d10-cd98-11ea-90d5-0a9cd3354c10"
      }
  }
]

    YAML

    ResourceType: 'AWS::CloudFormation::Stack'
  LogicalResourceId: NestedStack
  ResourceIdentifier:
    StackId: >-
      arn:aws:cloudformation:us-west-2:12345678910:stack/mystack/5b918d10-cd98-11ea-90d5-0a9cd3354c10

  3. To create a change set, use the following create-change-set command and replace the placeholder text. For the --change-set-type option, specify a value of IMPORT. For the --resources-to-import option, replace the sample JSON string with the actual JSON string you just created.

    > aws cloudformation create-change-set
    --stack-name TargetParentStackName --change-set-name ImportChangeSet
    --change-set-type IMPORT
    --resources-to-import "[{\"ResourceType\":\AWS::CloudFormation::Stack\",\"LogicalResourceId\":\"NestedStack\",\"ResourceIdentifier\":{\"StackId\":\"arn:aws:cloudformation:us-west-2:12345678910:stack/mystack/5b918d10-cd98-11ea-90d5-0a9cd3354c10\"}}]"
    --template-body file://TemplateToImport.json
    Note

    --resources-to-import doesn't support inline YAML.

    Alternatively, you can use a file URL as input for the --resources-to-import option, as shown in the following example.

    --resources-to-import file://ResourcesToImport.txt

  4. Review the change set to make sure the correct stack is being imported.

    > aws cloudformation describe-change-set --change-set-name ImportChangeSet

  5. To initiate the change set and import the stack into the source parent stack, use the following execute-change-set command and replace the placeholder text. Any stack-level tags are applied to imported resources at this time. On successful completion of the import operation (IMPORT_COMPLETE), the stack is successfully nested.

    > aws cloudformation execute-change-set --change-set-name ImportChangeSet
    Note

    It's not necessary to run drift detection on the parent stack after this import operation because the AWS::CloudFormation::Stack resource is already managed by AWS CloudFormation.