I have a bunch of old Rpi 3B's in a 19" 1RU rack space i use for toy clustering. PoE splitters from a PoE switch to power them which also provides the network uplink. All very neat and self contained and when it comes times to upgrade/replace if they all fail (i have a couple of spares) I can just pull out the 1RU for disposal.

Intel NUC's are probably much better value for money these days but the 3B's were pretty cheap at the time I bought them.