Moving APOLO off VMware without turning anything off

I moved seven machines at APOLO from VMware ESXi to Proxmox with zero downtime. The virtualization licensing cost went to $0, so APOLO no longer pays for its hypervisor, and the researchers who share its clusters didn't lose a service along the way. Then I tuned kernel and operating-system parameters, and average node load on equivalent workloads dropped from 55% to 35%.

APOLO is the scientific computing center where I did my internship, and this migration was my internship project. My work covered two clusters, APOLO 2 and APOLO 3, and the services that keep them usable, like FreeIPA, which handles logins to the clusters, and a central Prometheus collector that feeds a Grafana server for monitoring.

The move itself was one step of several. First I evaluated Proxmox as the new platform and prepared the migration. Then I converted the machines from ESXi to Proxmox while the services kept running. Once everything was on Proxmox, I tuned the kernel and OS parameters and checked the result.

In the same environment I configured the Proxmox firewall and UFW to restrict unwanted traffic. I also kept the virtual-machine backups in a protected location on the NAS. If a host or a service fails, those backups are the way back.

The load figure comes from production. Average node load was compared on the two hypervisor environments, the old ESXi one and the new Proxmox one, running equivalent workloads: 55% before, 35% after. That's 20 percentage points, about 36% less load than where it started.

What I like about this comparison is that both sides ran the same kind of work. The platform underneath changed, and so did the tuning, and I count the 20 points as one result of the two together.

When the internship ended in Feb 2026, I stayed at APOLO as a Supercomputing Research Assistant, with the same core responsibilities, until Jul 2026. So Proxmox, the platform I had evaluated, migrated to and tuned, stayed my responsibility for five more months.

I think that counts as a fair test: the same person who evaluated Proxmox, migrated to it and tuned it was also the one who had to keep it running for the next five months.