Hi all, I just packaged up the AWS SSM agent , which is a cool system for automated management of fleets of machines both in AWS and outside of it, allowing you to run commands on all of them, check "inventory" across all of them automatically, set policies on disparate types of machines, and so on.
NixOS seems to work fine with it and I can run commands on it and keep an eye on the current NixOS release by injecting a fake lsb_release into its path. But one of the features of SSM is the ability to take an inventory of "installed" packages on a system. Of course, that notion doesn't directly make sense in NixOS, but it got me wondering what sorts of metrics might make sense from a "keep an eye on your fleet of NixOS systems" perspective. Some possibilities: 1. Track runtime dependencies of the system root, and ideally maintain an external mapping of all of those hashes to expressions that produce them. The first part I know how to do, but the second part seems tricky. 2. Monitor "GC state" of your NixOS system: count how many unreferenced derivations are in the store and how much disk space past system generations retain (factoring in hard linking and such) 3. Dump current systemd unit state (broader than just NixOS, obviously) 4. Track total time spent building derivations and downloading substitutes: could be helpful to understand that some of your machines aren't accessing your binary cache properly. Perhaps also a "binary cache hit rate" metric. Does anyone have others? If you manage a large fleet of NixOS machines (and possibly other types of OSes too, so NixOps might not be suitable), which metrics do you find useful? Even if you do use NixOps to manage the state of your machines, ongoing metrics can still be useful for assessing the health of your systems. You don't want to be surprised by a machine's drive filling up because its store is full of junk :) Thanks, Dan  https://aws.amazon.com/ec2/systems-manager/
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