The way you usually solve this is by having sane defaults, and giving users different mechanisms for configuration based on how complex their configuration needs are. This can take a tiered approach.
As an example, simpler and straight forward things (such as disable egress traffic from S3 if the bill exceeds X) can be in the UI itself. Then, for customers who need more control, an option to configure via json or yaml similar to cloud formation. For anyone who needs even more giving an option to call a customer defined lambda function would give them the ability to at any metrics and take appropriate action.
Engineering problems:
1. How do you actually have a billing system reach out to every other system? It has to resolve the resource, network with it, have IAM permissions, a network route, etc.
2. How do you handle consistency?
3. How do you make it responsive?
4. How do you add this to every billable entity?
I mean, it's just a shitload of work, and all of that just to get to a terrible idea.
> The way you usually solve this is by having sane defaults, and giving users different mechanisms for configuration based on how complex their configuration needs are. This can take a tiered approach.
The sane default is you pay for what you use, and you can listen to billing events and build all of the logic you're talking about if you want to.
My point is that it is definitely an engineering problem as well as a product problem.
a) It's going to be super technically difficult to build (especially in a way where it's responsive at a granular basis to handle huge blow-up bursts)
b) It's not even clear what you're supposed to be building
None of what people are proposing is well defined or easy to build.