How to import Existing AWS Resources into a CloudFormation Stack

CloudFormation is a service that allows you to create and manage AWS resources using templates. You can use CloudFormation to automate the deployment and configuration of your applications and infrastructure.

But what if you have some existing AWS resources that you want to include in your CloudFormation stack? For example, you may have created a DynamoDB table or an S3 bucket manually or using another tool, and you want to bring them under CloudFormation management.

In this blog post, we will show you how to incorporate existing AWS resources into a CloudFormation stack using the resource import feature. We will also explain the benefits and limitations of this feature, and provide some tips and best practices.

What is Resource Import?

Resource import is a feature that allows you to bring existing AWS resources into CloudFormation management without having to delete and re-create them as part of a stack. You can use resource import to manage your resources using CloudFormation regardless of where they were created.

Resource import works by creating a change set that imports your existing resources into a stack or creates a new stack from your existing resources. You need to provide the following information during the import operation:

• A template that describes the entire stack, including both the original stack resources and the resources you are importing. Each resource to import must have a DeletionPolicy attribute in your template.
• Identifiers for the resources to import. You need to provide two values to identify each target resource: an identifier property and an identifier value. The identifier property is a resource property that can be used to identify each resource type, such as BucketName for an S3 bucket. The identifier value is the actual property value of the target resource, such as MyS3Bucket.

You can use the AWS Management Console, the AWS Command Line Interface (CLI), or the AWS CloudFormation API to perform the import operation.

Why Use Resource Import?

Resource import can help you achieve several benefits, such as:

• Consistency: You can use CloudFormation to manage all your AWS resources in a consistent and declarative way, regardless of how they were created.
• Automation: You can use CloudFormation to automate the deployment and configuration of your existing resources, as well as any new resources you may add in the future.
• Version control: You can use CloudFormation to track the changes and updates of your existing resources, as well as any dependencies or relationships between them.
• Reusability: You can use CloudFormation to reuse your existing resources in different environments or scenarios, such as testing, staging, or production.

What are the Limitations of Resource Import?

Resource import also has some limitations that you need to be aware of, such as:

• Not all AWS resources support import operations. You can check the list of supported resources here: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/resource-import-supported-resources.html
• You cannot import nested stacks or stacks that have children. You can only import resources into top-level stacks.
• You cannot modify existing parameters that initiate a create, update, or delete operation during the import operation. This may cause the import operation to fail.
• You cannot use the intrinsic function Fn::Transform when importing resources using the AWS Management Console. You need to use the AWS CLI or the API instead.
• You need to verify that the resources and their properties defined in the template match the intended configuration of the resource import to avoid unexpected changes.

How to Import Existing Resources into a Stack?

In this section, we will show you how to import an existing DynamoDB table into a CloudFormation stack using the AWS Management Console. We will assume that you have already created a DynamoDB table called Games manually or using another tool, and you want to include it in your CloudFormation stack.

The steps are as follows:

1. Sign in to the AWS Management Console and open the CloudFormation console at https://console.aws.amazon.com/cloudformation.
2. On the Stacks page, choose the stack you want to import resources into. If you don’t have an existing stack, you can create one using a template that describes your original stack resources.
3. Choose Stack actions, and then choose Import resources into stack.
4. Review the Import overview page, and then choose Next.
5. On the Specify template page, provide your updated 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 each target resource.
   • Under Identifier property, choose TableName for the DynamoDB table resource type.
   • Under Identifier value, type Games for the actual table name of the target resource.
   • Choose Next.
7. On the Specify stack details page, update any parameters if needed, and then choose Next. This automatically creates a change set.
8. On the Review stack-name page, review the resources to import, and then choose Import resources.

If the import operation is successful, you will see a message that says “The following resources have been imported into this stack”. You can then view the details of your imported resources in the Resources tab of your stack.

Tips and Best Practices for Resource Import

Here are some tips and best practices to help you use resource import effectively:

• Before importing resources, make sure that they are not part of another stack in the same region. CloudFormation does not allow you to import resources that belong to another stack.
• Before importing resources, make sure that they are not associated with any other AWS services or features that may interfere with the import operation. For example, you cannot import a DynamoDB table that is part of a global table or a backup plan.
• Before importing resources, make sure that you have the required permissions to perform the import operation. You need to have the cloudformation:ImportStackResources permission, as well as the permissions for the target resources and their dependencies.
• Before importing resources, make sure that you have a backup of your existing resources and their configuration. You can use AWS Backup or other tools to create backups of your resources.
• After importing resources, make sure that you test your stack and verify that everything works as expected. You can use CloudFormation drift detection or other tools to check for any configuration differences between your stack and your actual resources.

Conclusion

In this blog post, we have shown you how to incorporate existing AWS resources into a CloudFormation stack using the resource import feature. We have also explained the benefits and limitations of this feature, and provided some tips and best practices.

We hope this post has helped you understand how to use CloudFormation to manage your existing AWS resources. If you have any questions or feedback, please leave a comment below.