> It means that you can't spin up a stack for an hour if the system calculates that leaving it online for a whole month would breach your limit.
Sort of related, another wishlist feature I have is a way to start an EC2 instance with a deadline up front, and have the machine automatically suspended or terminated if it exceeds the deadline. I have some programs that start an EC2 instance, do some work, and shut it down (e.g. AMI building), and I would sleep a tiny bit better at night if AWS could deadline the instance as a backstop in case my script unexpectedly died before it could.
> Also you have variable costs (like s3 traffic)
Yeah, that's what I mean by it wouldn't solve the problem of usage-based billing. There they could just cut you off, and I think that's the bargain that people who want hard caps are asking for (there is always a spend cap at which I'd assume something had gone horribly wrong and would rather not keep spending), but I agree that the lack of real-time billing data is probably what stops them there.