Before buying all the nodes of the cluster, it is worth testing a unit. The short list of candidates was quickly drawn:

• Rock64 (ARM)
• Raspberry PI (ARM)
• Rock PI-X (X86_64)

The latter is my favorite because of the CPU architecture and also because every Linux distribution can be installed on it.
Therefore, I bought one and here it is:

Tests are successful:

• I ran a Ubuntu 20.04 distribution with included Kubernetes instance without any problem.
• The server power unit did the job.
• Dissipated heat stayed at a low level event under stress but the proposed heat sink is affordable (7$) and I won’t take risk.

The only drawback is that Rock PI-X model A, without wifi thus allowing to save à few dollars, are not available for purchase.