feat(sns-subscriptions): cross-region support for Lambda functions

[njlynch]

Commit Message

feat(sns-subscriptions) cross-region support for Lambda functions (#7679)

fixes #5734

End Commit Message

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[nija-at]

Thanks for submitting this PR!

Code itself looks good to me.
Did you happen to check if this actually works, as in CF doesn't complain at the time of deployment, and that a message on a topic in one region actually invokes the function in another?

[njlynch]

Did you happen to check if this actually works, as in CF doesn't complain at the time of deployment, and that a message on a topic in one region actually invokes the function in another?

Yes. I created a SNS topic in eu-west-2 (by hand), built a CDK app with a Lambda function that subscribed to the topic, and deployed it to eu-west-1. Verified it broke prior to the fix, and worked afterward (both deploying correctly, and being able to trigger the Lambda via the topic).

[iph]

What service principle is used when adding permissions for sns from cloudformation?

This may be a future issue to add but cross-region in newer regions (ap-east-1, me-south-1, af-south-1, eu-south-1, etc.), I'm unsure if the overarching service principle (e.g. sns.amazonaws.com) works and I think you need to use regionalized SP. This isn't a problem in same-region so it wouldn't need to be addressed.

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