
Amazon adds message filtering to SNS - nicwolff
http://docs.aws.amazon.com/sns/latest/dg/message-filtering.html
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inopinatus
Reminder that SNS has at-least-once semantics, not just in theory but in
practice: we have FaaS instances that see duplicates from SNS several times a
day.

So if you are using SNS as a pub/sub bus for any kind of transactional
activity (as in the examples above, where it's used for delivery of
order_placed messages), be sure to build in some dupe-detection. The window
seems to be on the order of minutes and I presume it's due to some distributed
aspect of SNS internals. We keep MessageId history for a day for duplicate
detection.

This is also why we won't use SNS for SMS to end-users, where a dupe would
throw shade on us. We treat it strictly as a message fan-out for internal use.

