There exist special UPSes that you can attach to a power line of a server, unplug and unmount it, and keep the server powered all the time, without the server being able to detect that.
If you are really serious about security, you need to have a watchdog on network link downtimes because, no matter what, you can't disrupt a fiber optic network link without the server noticing.
If you are really serious about security, you need to have a watchdog on network link downtimes because, no matter what, you can't disrupt a fiber optic network link without the server noticing.