AppEngine instances can typically start in 30 seconds or so. So if your spike is because your video went viral on facebook and lots of people are looking it it, that's fine.
If your spike is because you have 10 million clients with an app set to do an HTTP request at exactly 10:00:00pm, and they all arrive within a quarter second, thats a problem.
30 seconds is actually a gross overestimate for AE startup. Your description of our problem is very accurate, though. We still need to over-provision just before the spike, which we do with a cron that scales up to several hundred instances 5 minutes before 10pm and then back down to normal levels 5 minutes after. Autoscaling takes care of the rest.
AppEngine instances can typically start in 30 seconds or so. So if your spike is because your video went viral on facebook and lots of people are looking it it, that's fine.
If your spike is because you have 10 million clients with an app set to do an HTTP request at exactly 10:00:00pm, and they all arrive within a quarter second, thats a problem.