Often, when things have gone really wrong (DoS, internal network issues, app errors, disk full) the affected machine(s) stop reporting to graphite (or under-report data). We get alerted by monitoring the services, not the stats.
Being alerted about low or unusual values might be helpful in some cases, but based on my experience, it would too noisy. Usually when something bad happens, we anyway investigate Graphite and analytics tools to understand the impact on traffic and KPIs.
I could see Rearview being useful for some cases, but not as a replacement for real monitoring and alerting tools.
I'll peek at the pull requests and see if my company might be able to contribute some help.
Pingdom will tell you that your engine just threw a rod. Rearview will tell you your rods are knocking before that happens.
Why not a full ruby stack, or was the "live" scripting done after the initial inception?
Ah. I've usually just used email for that. :)
the UI is quite polished