CloudFormation Cross-Region Reference

CDK 2.x

There is a new Stack property called crossRegionReferences which you can enable to add cross region references. It's as simple as this:

const stack = new Stack(app, 'Stack', {
  crossRegionReferences: true,
});

Under the hood, this does something similar to the above answers by using custom resources and Systems Manager. From the CDK docs:

crossRegionReferences?
Enable this flag to allow native cross region stack references.

Enabling this will create a CloudFormation custom resource in both the producing stack and consuming stack in order to perform the export/import

This feature is currently experimental

More details from the CDK core package README:

You can enable the Stack property crossRegionReferences in order to access resources in a different stack and region. With this feature flag enabled it is possible to do something like creating a CloudFront distribution in us-east-2 and an ACM certificate in us-east-1.

When the AWS CDK determines that the resource is in a different stack and is in a different region, it will "export" the value by creating a custom resource in the producing stack which creates SSM Parameters in the consuming region for each exported value. The parameters will be created with the name '/cdk/exports/${consumingStackName}/${export-name}'. In order to "import" the exports into the consuming stack a SSM Dynamic reference is used to reference the SSM parameter which was created.

In order to mimic strong references, a Custom Resource is also created in the consuming stack which marks the SSM parameters as being "imported". When a parameter has been successfully imported, the producing stack cannot update the value.

CDK 1.x

If you are on CDK 1.x, continue using the workaround that others have shared.