Proxmox VE, what it is for and how to stand up a cluster
Opselis
Proxmox VE is a KVM and LXC hypervisor with a web panel. Why a cluster, how corosync and pmxcfs work, how to install a node, join a second host and clone the first machine from a template.
Proxmox VE is a virtualisation platform on Debian. On a physical server it runs KVM machines and LXC containers. The web panel (port 8006) shows nodes, CPU, RAM, disks and guests. You use it to build a private cloud: your own VMs, templates, snapshots, migration between hosts, without vSphere and without hand-rolled libvirt.
What it is for
You use Proxmox VE when you need many systems on a few servers: store, database, staging, jump host, monitoring. One node is enough for a test. A cluster (three nodes, or two plus a qdevice) gives quorum, live migration and HA. A template with cloud-init repeats the same image. A snapshot rolls back a change on the same disk. Long-term copy is Proxmox Backup Server, in a separate post.
How it works
The host runs a Proxmox kernel. KVM emulates hardware for a VM (the guest has its own kernel). LXC shares the host kernel, lighter, weaker isolation. Cluster config lives in pmxcfs (/etc/pve) and travels over corosync. Quorum: with three nodes, losing one is survivable. With two and no qdevice, a lost link splits the cluster. Storage is local (LVM-Thin, ZFS) or shared (NFS, Ceph). Live migration without shared disk copies the volume on the fly and takes longer.
How to set it up
Install the Proxmox VE ISO on a bare server. Hostname, management address, vmbr0 on the NIC. Panel: https://host-address:8006. In Datacenter, Permissions add a named user. In Two Factor enable TOTP. Keep root for recovery, not for daily work.
Cluster: Datacenter, Cluster, Create Cluster. Put cluster traffic on a separate NIC or VLAN, not on the guest bridge. On the second host: Join Information, then Join Cluster. In Datacenter both nodes online, quorum OK.
Storage: Datacenter, Storage, Add. For a test, local-lvm is enough. For production, NFS or Ceph if the VM must migrate. First VM: Create VM, Debian ISO, vmbr0, QEMU Guest Agent. After install, install qemu-guest-agent in the guest. Convert to Template, further machines via Clone and cloud-init (IP, SSH key).
LXC for light services. Magento and the database on KVM. Turn HA on a VM only with shared storage and an address that moves with the machine. Cluster operations: IT administration.