Fn::GetStackOutput: How CloudFormation and CDK Solved Cross-Region References Together One String, Two Regions Your ACM certificate must live in us-east-1. Your app runs in ap-northeast-1. You need the certificate ARN in your CloudFront distribution. How do you pass it? Stack A (us-east-1) Stack B (ap-northeast-1) ┌─────────────────────┐ ┌─────────────────────┐ │ │ │ │ │ ACM Certificate │───── ? ───────▶│ CloudFront Dist │ │ (must be us-east-1)│ │ (needs cert ARN) │ │ │ │ │ └─────────────────────┘ └─────────────────────┘ Enter fullscreen mode Exit fullscreen mode Until recently, composing this relationship natively in a template required extra plumbing. Fn::ImportValue only works within the same account and region. Cross that boundary and you needed workarounds — custom resources, Lambda functions, SSM parameters, IAM roles, all to pass a single string. This wasn't something CDK could solve alone. It needed a new CloudFormation primitive.…