My intro to Openstack was a talk by someone using 12 HP micro servers in his office.
- They are quiet enough.
- Have an internal USB port to put the OS boot on so all 4 disk bays could be storage
- Have IPMI (iLO/iDRAC) so remote power toggle can work
= He got an addressable PDU bcause the IPMI wasn't reliable enough
- Have a PCIe x1 for a gigabit ethernet card
= there are 1 and 2 port gigabit ethernet cards that work for < $50
- RAM could be upped to 8 GB (later systems can do more)
He added 1 or 2 network switches and was able to power & run it in his office.
I think one node is a provisioning server so everything could be PXE booted. If you don't have that, I'd want an IPMI that can use virtual storage and remote console. Supermicro IPMI comes with it (and I've found the power toggle to be reliable enough). iDRAC is a license. Desktops typically do not have IPMI.
I think you'd want at least 2 network ports for your nodes and 3+ on the controller.
The limiting factor will be RAM, not cores. I'll take a 32 GB quad core system over a 12 core 16GB system.
FWIW - does anyone know of a < $500 system (motherboard, cpu, power, case) that can go to 64 GB?