We've been using Proxmox VE ( https://pve.proxmox.com/wiki/Main_Page https://pve.proxmox.com/wiki/Main_Page ) in production for a while. It's open source and f

We've been using Proxmox VE ( https://pve.proxmox.com/wiki/Main_Page https://pve.proxmox.com/wiki/Main_Page ) in production for a while. It's open source and free, and is a tweaked Debian with KVM/QEMU virtualization and also LXC container support. It puts a nice web interface on top of it all, but the underlying OS and CLI is fully available too. The hosts can be clustered and VMs can be migrated. It doesn't require shared storage but can use it if you have it. (You need shared storage for live migrations). We pay for support since the cost is reasonable, but you don't have to.