Nesting an existing stack - AWS CloudFormation

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 cannot import a stack into a child stack or import a stack that has children.

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.

    { "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 StackName property.

    2. Under Identifier value, type the actual property value. For example, my_stack.

      
                        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 trigger a create, update, or delete operation.

  8. On the Review stack-name 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::Stackresource 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.

    { "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. Create a change set of type IMPORT with the following parameters. --resources-to-import does not support inline YAML.

    > aws cloudformation create-change-set --stack-name TargetParentStack --change-set-name ImportChangeSet --change-set-type IMPORT --resources-to-import "[{\"ResourceType\":\AWS::CloudFormation::Stack\",\"LogicalResourceId\":\"MyStack\",\"ResourceIdentifier\":{\"StackId\":\"arn:aws:cloudformation:us-east-2:123456789012:stack/mystack-mynestedstack-sggfrhxhum7w/f449b250-b969-11e0-a185-5081d0136786\"}}] --template-body file://templateToImport.json

    The AWS CLI also supports text files as input for the resources-to-import parameter, as shown in the following example.

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

    In this walkthrough, file://resourcesToImport.txt contains the following.

    [ { "ResourceType":"AWS::CloudFormation::Stack", "LogicalResourceId":"MyStack", "ResourceIdentifier": { "StackId":"arn:aws:cloudformation:us-east-2:123456789012:stack/mystack-mynestedstack-sggfrhxhum7w/f449b250-b969-11e0-a185-5081d0136786" } } ]
  3. Review the change set to make sure the correct stack is being imported.

    > aws cloudformation describe-change-set --change-set-name ImportChangeSet
  4. Execute the change set to import stack into the source parent stack. 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::Stackresource was already managed by AWS CloudFormation.