Dead letter sns topic never called with gateway lambda nodejs

I’m encountering a strange situation.
I have a gateway lambda (nodejs8) that is configured with onError to send dead letter queue notifications to an SNS topic.
Configuration seems to be fine, the lambdas have been given all permissions on sns.

The lambda throws an error, the error shows in the logs however the sns notification is not sent on the designated topic.
The DeadLetterErrors topic metric is not incremented either.

Any thoughts on how can this happen? According to the documentation if the error handling via SNS is faulty at least the DeadLetterErrors metric should be affected.


I’ve figured it out. DLQ only works for asynchronous lambda invocations.
Gateway invocations are synchronous.