Proxmox VE 2.0 Cluster

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Proxmox VE 2.x (and all versions above, including 3.x) Cluster enables central management of multiple physical servers. A Proxmox VE Cluster consists of several nodes (up to 16 physical nodes, probably more).

Main features

  • Centralized web management, including secure VNC console
  • Support for multiple authentication sources (e.g. local, MS ADS, LDAP, ...)
  • Role based permission management for all objects (VM´s, storages, nodes, etc.)
  • Creates multi-master clusters (no single master anymore!)
  • Proxmox Cluster file system (pmxcfs): Database-driven file system for storing configuration files, replicated in real-time on all nodes using corosync
  • Migration of Virtual Machines between physical hosts
  • Cluster-wide logging
  • RESTful web API


  • All nodes must be in the same network as it uses IP Multicast to communicate between nodes (See also Corosync Cluster Engine). Note: Some switches do not support IP multicast by default and must be manually enabled first. See multicast notes for more information about multicast.
  • Date and time have to be synchronized
  • SSH tunnel on port 22 between nodes is used
  • VNC console traffic is secured via SSL, using ports between 5900 and 5999
  • If you are interested in High Availability also, for reliable quorum you must have at least 3 active nodes at all times, or use a qdisk as seen in Two-Node_High_Availability_Cluster

Proxmox VE Cluster

First, install the Proxmox VE nodes, see Installation. Make sure that each Proxmox VE node is installed with the final hostname and IP configuration. Changing the hostname and IP is not possible after cluster creation.

Currently the cluster creation has to be done on the console, you can login to the Proxmox VE node via ssh.

All settings can be done via "pvecm", the Proxmox VE cluster manager toolkit.

Create the Cluster

Login via ssh to the first Proxmox VE node. Use a unique name for your Cluster, this name cannot be changed later.


pvecm create YOUR-CLUSTER-NAME

To check the state of cluster:

pvecm status

Adding nodes to the Cluster

Login via ssh to the other Proxmox VE nodes. Please note, the node cannot hold any VM that has the same ID of a VM on another node (otherwise you will get conflicts with identical VMID's - to workaround, use vzdump to backup and to restore to a different VMID after the cluster configuration).

Add a node:


For IP-ADDRESS-CLUSTER use an IP from an existing cluster node.

To check the state of cluster:

pvecm status

Display the state of cluster:

pvecm status

 1 :   M     A    5 days 01:43   0.54    20%     1%     4%
 2 :   N     A    2 days 05:02   0.04    26%     5%    29%
 3 :   N     A           00:13   1.41    22%     3%    15%
 4 :   N     A           00:05   0.54    17%     3%     3%

Display the nodes of cluster:

pvecm nodes

Node  Sts   Inc   Joined               Name
   1   M    156   2011-09-05 10:39:09  hp1
   2   M    156   2011-09-05 10:39:09  hp2
   3   M    168   2011-09-05 11:24:12  hp4
   4   M    160   2011-09-05 10:40:27  hp3

Remove a cluster node

Move all virtual machines out of the node, just use the Central Web-based Management to migrate or delete all VM´s. Make sure you have no local backups you want to keep, or save them accordingly.

Log in to one remaining node via ssh. Issue a pvecm nodes command to identify the nodeID:

pvecm nodes

Node  Sts   Inc   Joined               Name
   1   M    156   2011-09-05 10:39:09  hp1
   2   M    156   2011-09-05 10:39:09  hp2
   3   M    168   2011-09-05 11:24:12  hp4
   4   M    160   2011-09-05 10:40:27  hp3

Issue the delete command (here deleting node hp2):

pvecm delnode hp2

If the operation succeeds no output is returned, just check the node list again with 'pvecm nodes' (or just 'pvecm n').

ATTENTION: you need to power off the removed node, and make sure that it will not power on again.

Re-installing a cluster node

Move all virtual machines off the node.

Stop the following services:

service pvestatd stop
service pvedaemon stop
service cman stop
service pve-cluster stop

Backup /var/lib/pve-cluster/

tar -czf /root/pve-cluster-backup.tar.gz /var/lib/pve-cluster

Backup /root/.ssh/ , there are two symlinks here to the shared pve config authorized_keys and authorized_keys.orig , you need not worry about these two yet as they're stored in /var/lib/pve-cluster/

tar -czf /root/ssh-backup.tar.gz /root/.ssh

Shut server down & re-install. Make sure the hostname is the same as it was before you continue.

Stop the following services:

service pvestatd stop
service pvedaemon stop
service cman stop
service pve-cluster stop

Restore the files in /root/.ssh/

tar -xzf /root/ssh-backup.tar.gz

Replace /var/lib/pve-cluster/ with your backup copy

rm -rf /var/lib/pve-cluster
tar -xzf /root/pve-cluster-backup.tar.gz

Start pve-cluster & cman:

service pve-cluster start
service cman start

Restore the two ssh symlinks:

ln -sf /etc/pve/priv/authorized_keys /root/.ssh/authorized_keys
ln -sf /etc/pve/priv/authorized_keys /root/.ssh/authorized_keys.orig

Start the rest of the services:

service pvestatd start
service pvedaemon start

Working with Proxmox VE Cluster

Now, you can start creating Virtual Machines on Cluster nodes by using the Central Web-based Management on any node.



  • Date and time have to be synchronized (check "ntpdc -p")
  • Check /etc/hosts for an actual IP address of a system

Two nodes cluster and quorum issues

The problem

If you have to bring down a node of a cluster which normally have two nodes, even if not under HA, you have to take the quorum in account, as in this section

If you have a two nodes cluster, not HA, by default you will have something like this

# pvecm status
Version: 6.2.0
Config Version: 2
Cluster Name: pvecluster
Cluster Id: 48308
Cluster Member: Yes
Cluster Generation: 92
Membership state: Cluster-Member
Nodes: 1
Expected votes: 2
Total votes: 1
Node votes: 1
Quorum: 2 Activity blocked
Active subsystems: 5
Ports Bound: 0
Node name: pve2
Node ID: 1
Multicast addresses:
Node addresses:

When you bring one node down, maybe after you live migrated all vm/CT to the other node, your cluster becomes "non operational": you cannot add vms, all backups will fail, possibly more! One of the syntoms is: you get messages from the up pve node that it can't write in many places where it is normally expected to be able to, such as:


because permissions became "read-only"!

That is because as of the above default config, 2 votes are needed, each node counts 1, and you have only 1 node of two alive!

The solution


clustering is not an easy concept, and many things can (and will) go wrong, ranging from locked to destroyed, if you don't know exactly what you are doing. Applying the following solution could make the cluster run into a split brain, because each node is allowed to update values without having quorum.

That said, this is a good (not brief) intro to HA clustering, using tools similar to those PVE uses today 2-Node Red Hat KVM Cluster Tutorial.

The simple solution is to "tell" to the cluster that you expect just 1 vote for the cluster to be operational: you can do this permanently, following instructions in this section to add

two_node="1" expected_votes="1" parameters in the <cman> start tag

but until you get back alive the "down" node, you can't validate and apply the new config from the web GUI

if you need, you can temporarily update the "expected" part of the pve cluster config issuing a simple command:

#pvecm expected 1

that will instantly restore write permissions where thay should be, backups should work again, and all.

Another solution would be to add a third "dummy node", which also counts 1, in a way similar to HA setups but without fencing, but that would take us slightly "off topic", because this section is named "Two nodes cluster and quorum issues"

Video Tutorials

Proxmox VE Youtube channel