Researchers have built server prototypes that re-use old components

I have a rack in a datacenter with mostly 5 year old Supermicro servers. We bought them all off of Ebay for no more than $400 each. They work great and we have more compute and bandwidth for our workloads for less than $1000 a month. If we used one of the could providers it would be many thousands of dollars per month. I understand not everyone has the skills to run their own rack but the value of doing so is totally worth it.

I for one never learned to do it.

IMO there's a big historical and archival value in the idea to start cataloguing such knowledge.

What skills do you need to run your own rack?

That depend on context. Is it your own rack in your own data center or rented space in someone else data center? A rack in a AC cooled office room? What uptime is required? What redundancy is required? What are the network requirements? Any environmental concerns (power loss, flooding, extreme heat overpowering the ac, travel distance for personal)? How do you want to manage personal during night/weekends/holidays? What is the distance to shops that has spare parts? Access to backup power?

Most of it can be fairly simple to solve or risk manage if the company is small, people are flexible, and the uptime requirements are not that strict or there is sufficient backup solutions. If its just owning your own rack in a rented space in a data center then the difference is fairly minor, as well as the cost savings.

Agreed! And there's this space in the middle there...Because at the dayjob/enterprise side of things there's the concepts of hypervisor vendors, CoLos (co-locating servers in data centers), and full-blown enterprise on-premise...and of course other end of spectrum is homelabbing/that is self-hosting stuff at home either on consumer or old server grade computers...but what if i want to have a single server for my own self-hosting use but in a tiny data center/colo, but which is not outlandish, and i would maintain it myself? I dont know what we'd call that space: mini-CoLo, or self-data centering, or remote-homelabbing? but, i'm sure there's a gap in knowledge there, and would be great to learn more. :-)

I imagine with Linux this might be less of an issue than Windows, but at least with Windows you see that Dell etc stop supporting newer Windows Server versions on older servers.

Regardless, security issues in out of band management systems might also not get patched.