I'm fortunate to be in an area that runs 10 gigabit Internet to the home. Unfortunately that means off the shelf hardware to act as a firewall/router isn't cheap, so I white boxed it. Was running the Mellanox card with an old Ivy Bridge system I had on hand and was only pushing 4/5 gigabits (which shows as 7 gigabit on Netflix's speed test). Upgraded to Ryzen 3rd gen and now pushing 9 gigabits on the same test (hilariously reads as 13/14 gigabits). Something you pretty much never see tested in reviews.
RAM is 2666MTs Samsung B-die ECC which is overclocked to 3200MTs CL 18-17-17-17-21-53 @ 1.2V. Could probably go faster, but no need to.
Motherboard was chosen before I found the chassis, and most DIY 2U chassis are mATX. Could have changed it, but decided since I didn't need anything more than the X570M Pro4 may as well vote for the form factor and hopefully encourage better offerings in the future.
The CPU doesn't matter a whole lot here. At least if htop is to be believed it's mostly idling even when forwarding 10 gigabit of traffic. Went 3rd gen mostly to have the latest PCIe controller. Will admit that the halved write speed worried me that I might need to use a 2nd gen or APU instead, but in the end it seems to do its job just fine.
Video card is a rescue from a box of garbage. It's a garbage card so was a fitting place to find it, but given that the Linux drivers for it are fine and literally all it needs to do is display text there was no need for anything more. But for those curious I did run Doom on it (classic, GZDoom) and lets just say the software renderer was faster, and even then was bottle-necked by the speed the frame could be transferred to vram.
Hard drive is also a salvage. Don't see a need to change it since the machine rarely ever does disk IO.
Using a Mellanox ConnectX-5 since compared to the 3 or 4 there were a few features that piqued my interest. Not sure if I'll ever actually get around to playing with them, but they're there. Practically speaking though this build would likely have worked just as well with a ConnectX-3 or 4 which are much cheaper 2nd hand.
As I said in the first paragraph, the build works well. About my only complaint is that I can't disable the on board LAN, which is an extremely minor gripe since there's not really any advantage to disabling it besides looking slightly cleaner in the OS.
Figured it would be funny to post something completely different from the norm on here.