Every now and then I like finding links between Cybernetics (or Systems Dynamics, or Systems Thinking, pick your favorite variation) and System Administration. I am not the only one in this. For example Matt Simmons has written about how System Administrators act as homeostasis mechanisms for the systems they manage. And minutes before this slide came up my way:
Rule #4: Monitoring systems need to be more available and scalable than the systems being monitored
which reminded me of a theorem and a law as applied in the monitoring systems domain. The Good Regulator Theorem states that every good regulator of a system must be a model of that system. You provide the monitoring system with a model of what you need to monitor in its appropriate DSL or clickware. The more precise the model, the better the monitor.
The rule in the slide ties closely with the law of requisite variety where the variety in the control system must be equal to or larger than the variety of the perturbations in order to achieve control. Think about it: At least the downtime of your monitoring system needs to be significantly less than that of the system monitored. Otherwise what exactly are you seeing? Think of Nyqvist-Shannon sampling here. Or as John Gall has put it in The Systems Bible, a system is no better than its sensory organs.
Is it practical to make these observations? For everyday job not really, but when I find such connections between “obscure” theory (obscure for admins) and system administration, I always smile :)
PS: @adrianco during the discussion left another piece of advice:
on a later slide I said best to use two independent monitoring systems then they can watch each other.