SNS Delivering Messages to a Deleted Subscription

Question

I have an SNS topic with HTTPS subscriptions. The endpoint is an API that proxies a Lambda function, which formats and forwards the SNS message to a webhook (chat room). I was testing the unsubscribe functionality by following the 'UnsubscribeURL' link from the SNS 'Notification' and came across seemingly incorrect behavior.

• I follow (via browser) the UnsubscribeURL link.
• I see the XML response (in browser) indicating the unsubscribe request has been executed.
• I confirm the unsubscribe request has been executed by going to the AWS Console, looking at the SNS Topic, and seeing that the Subscription is now listed as "Deleted" (where previously it had an ARN and a link provided).
• I further confirm the subscription request has executed because I can see the receipt of the unsubscribe confirmation come through

However, subsequently when I then post a message to that Topic (whether via Console or AWS CLI), the message delivers to the Deleted Subscription (HTTPS endpoint).

¿Have others seen this behavior?

¿Have others found a solution or explanation?

Answer 1

This appears to be an issue of timing. I would have expected unsubscription (and resubscription) requests to be executed pretty much immediately (delay measured in seconds). However, after testing and waiting a bunch of times it seems as though there exists a delay that ranges anywhere from a few seconds up to ~10m.

While Subscription deletions and creations are effectively immediate, Subscription unsubscribes and resubscribes have a relatively significant delay much of the time.