Comment by ufmace

Personally, I don't think that capping costs explicitly is a good idea, because it doesn't carry enough information about what to do when you hit that cap.

Not even considering something like AWS with a bazillion types of services, say you have a cloud hosting service that runs nothing but auto-scaling clusters of servers billed by the hour. So I set a cap on costs but not cap on scaling up and turn it loose. It gets a hug of death from something, scales to the sky, does serve all of that traffic fine, but burns through my monthly cost cap in an hour. Oops, now it's down entirely for the next 3 weeks or whatever. Does anybody in the world who's willing to pay for hosting something actually want that? I have to doubt it.

On the other hand, capping the scaling size by number of hosts sounds pretty reasonable. Set a cap at say 2x your normal peak traffic. You get a hug from something, it hits the cap. Most of your extra traffic gets errors or really slow responses, but your service stays up, even when the traffic dies down. Your monthly costs are a bit higher than usual, but manageable. That sounds like a much better result to me.

That doesn't even get into stuff like, oh hey we dropped your DB server because you hit your cost cap early and it costs money to keep it running and to create a new backup too, hope you don't miss that data too much!