Thanks for the detailed writeup. I think projecting future costs would be hard but someone pointed out in previous comments that service specific rules ( EC2, S3) etc could be more realistic.
Also what do you think about AWS Cost Explorer API? It looks like it can provide monthly/daily charges and we can build rules for customer tolerance, like you mentioned.
> interesting, I was thinking I could poll billing metrics (total charges etc) to figure out account level charges.
If it were that easy, this would already exist ¯\_(ツ)_/¯
I think many people use AWS primarily for s3 and EC2 (and s3 costs are negligible for most side projects) so if you were picking a single service, EC2 would probably be the most broadly applicable (and IMO the most realistic one to actually build). On the other hand I would imagine that for many side project developers, their EC2 costs are the easiest to control - even if you do autoscaling, you can cap your max nodes.
What is most useful is tracking the total AWS spend because what really gets you is the service you weren't expecting to cost as much as it did, but that is a very very very hard problem.
I was looking at AWS Cost Explorer API, looks promising but don't know if it's granular enough.
after thinking about your comment on EC2, I think this tool could help smaller teams where you don't know who's doing what with the resources and you just need an upper limit of your monthly/daily spend.
about the last point, yes it's very hard to figure out. Also I thought most people check out the pricing page before trying out any aws services, wouldn't that give an estimate of what they are getting into (i.e. RDS, API gateway) ?
But again I always forget about the data transfer charges so you might be right about this.
I've used cost explorer enough to know that it lags meaningfully behind current costs, but you would probably have to do some measurements to know how much (I would guess several days). If you do that, remember that individual services (or even different components of a single service) might have different lag times. The cost explorer data seems pretty good though.
> I think this tool could help smaller teams where you don't know who's doing what with the resources and you just need an upper limit of your monthly/daily spend.
Yeah, definitely!
> But again I always forget about the data transfer charges
Yeah. AWS can have some pretty complex cost models since they charge based on the amount of resources you actually used - there are way more axes of cost than most people have time to think through.
If you end up building this, I suggest considering that many people will not want their resources automatically shut down, either because they want to serve the spike in traffic or because they are paranoid that there could be a mistake and have production infrastructure accidentally shut down. I would consider designing it so that users can choose to get a Slack message or something instead of having the resources shut down.
