As an infrastructure engineer, that seems like it would be overly complicated. You now need processes doing long polls or subscribing to SNS topics.

If you're polling the local metadata service, the longest you're waiting for an answer is 5 seconds, and you can immediately begin closing up your work properly to be most efficient about the compute time used.

That's what I get for commenting from my phone; I meant to say "I would have expected Amazon to publish two minute notices to a SNS topic."