Get values stored in other services using dynamic references - AWS CloudFormation
General considerations

Get values stored in other services using dynamic references

Dynamic references provide a convenient way for you to specify external values stored and managed in other services and decouple sensitive information from your infrastructure-as-code templates. CloudFormation retrieves the value of the specified reference when necessary during stack and change set operations.

With dynamic references, you can:

  • Use secure strings – For sensitive data, always use secure string parameters in AWS Systems Manager Parameter Store or secrets in AWS Secrets Manager to ensure your data is encrypted at rest.

  • Limit access – Restrict access to the Parameter Store parameters or Secrets Manager secrets to only authorized principals and roles.

  • Rotate credentials – Regularly rotate your sensitive data stored in Parameter Store or Secrets Manager to maintain a high level of security.

  • Automate rotation – Leverage the automatic rotation features of Secrets Manager to periodically update and distribute your sensitive data across your applications and environments.

General considerations

The following are the general considerations for you to consider before you specify dynamic references in your CloudFormation templates:

  • Avoid including dynamic references, or any sensitive data, in resource properties that are part of a resource's primary identifier. CloudFormation may use the actual plaintext value in the primary resource identifier, which could be a security risk. This resource ID may appear in any derived outputs or destinations.

    To determine which resource properties comprise a resource type's primary identifier, refer to the resource reference documentation for that resource in AWS resource and property types reference. In the Return values section, the Ref function return value represents the resource properties that comprise the resource type's primary identifier.

  • You can include up to 60 dynamic references in a stack template.

  • If you're using transforms (like AWS::Include or AWS::Serverless), CloudFormation doesn't resolve dynamic references before applying the transform. Instead, it passes the literal string of the dynamic reference to the transform, and resolves the references when you execute the change set using the template.

  • Dynamic references can't be used for secure values (like those stored in Parameter Store or Secrets Manager) in custom resources.

  • Dynamic references are also not supported in AWS::CloudFormation::Init metadata and Amazon EC2 UserData properties.

  • Don't create a dynamic reference that ends with a backslash (\). CloudFormation can't resolve these references, which will cause stack operations to fail.

The following topics provide information and other considerations for using dynamic references.

Topics