Enter the temperature compensated crystal oscillator (TXCO). A few $ at most should get you one.
This shouldn't be overkill for a server dedicated to timekeeping on a large company network, right?
In a datacenter one could even go for a matchbox sized atomic clock. Last I checked (years ago) such a miracle device could be had for ~$1500.
Then: how often does atomic clock (or even TXCO) fail, in practice? My guess: only about as often as even the backup power fails.
Note that either should provide accurate timekeeping without even going outside a physical location. That is: without using 'random' NTP server on the internet, GPS or whatever.
I've got a GPS-disciplined Oven Controlled Crystal Oscillator (OCXO) hooked up to a raspberry Pi running Chrony on my home network. It provides a pretty good time source (and more importantly for me a pretty good 10MHz reference). There are rack-mount 1U NTP servers built for the purpose for about what you estimate.
Most atomic clocks will have 20+ year lifetimes. OCXOs age out a good bit faster, but they're rather cheap (<$200 for ones good enough to provide holdover for a GPS module). TCXOs don't age as quickly (they're not literally in an oven), I'm not sure how long they can be expected to last.
This shouldn't be overkill for a server dedicated to timekeeping on a large company network, right?
In a datacenter one could even go for a matchbox sized atomic clock. Last I checked (years ago) such a miracle device could be had for ~$1500.
Then: how often does atomic clock (or even TXCO) fail, in practice? My guess: only about as often as even the backup power fails.
Note that either should provide accurate timekeeping without even going outside a physical location. That is: without using 'random' NTP server on the internet, GPS or whatever.