If that happens, is prometheus really the biggest of your worries here? Software breaks left and right when disks disappear from under them, I'm not sure this is neither unexpected or unique to prometheus.
> If the scrapers start to stall due to connection timeouts: what does prometheus do?
I'm having this "issue" all the time, as some of my WiFi connected (less important) cameras are just within the WiFi range, and I'm using prometheus to scrape metrics from them. It seems like the requests times out, then the next time it doesn't, and everything just works? What's the issue you're experiencing with this exactly?
> It's not acceptable as soon as lost data could be critically important in diagnosing major issues in billing systems, or actually billing users, or
Wait what? Billing systems? That stuff would go into your proper database, wouldn't it? Sure, if prometheus/node_exporter fails or whatever, you won't get metrics out of the host, but again, if those things start failing on that host, the host is having bigger issues than "prometheus suck at scale".
I was eagerly awaiting to be educated about potential gaps in my understanding of prometheus, instead it seems like you simply don't happen to like they way they do things? I was under the impression they did something wrong or something was broken, but these things just seems like the typical stuff you have to think about for any service you deploy.
That's not a general "software breaks when disks fail" situation: that's a monitoring system failing at its one job.
Your monitoring system failing silently when your infrastructure is under stress is precisely the failure mode that monitoring exists to prevent.
Zabbix solves this with native HA and self-checks. Prometheus makes it your problem to solve with external tooling, and most people don't, until they need it.
Of course the systems that have to alert me to failure have to be designed with mechanisms to alert me to the fact that they themselves are failing.
Zabbix, Nagios, Munin -- practically everything that existed before: understood this.
Prometheus doesn't because it optimised intentionally for being easy to deploy and for there being a hierarchy of prometheus's in a tree-like formation. Which makes sense, but forces a much more distributed and difficult to reason model.
Monitoring systems can't be designed for the happy path. By definition, they only matter when things are going wrong- which is precisely when the happy path isn't available. Prometheus is excellent when everything is fine (scaling aside). That's not when you need your monitoring system to be excellent.
But, I'm sure your setup makes as much sense in your context as mine makes in my context. As long as it works for you, we're all happy :)