pvecm(1)

Under Datacenter → Cluster, click on Create Cluster. Enter the cluster name and select a network connection from the dropdown to serve as the main cluster network (Link 0). It defaults to the IP resolved via the node’s hostname.

To add a second link as fallback, you can select the Advanced checkbox and choose an additional network interface (Link 1, see also Corosync Redundancy).

Login via ssh to the first Proxmox VE node and run the following command:

To check the state of the new cluster use:

It is possible to create multiple clusters in the same physical or logical network. Each such cluster must have a unique name to avoid possible clashes in the cluster communication stack. This also helps avoid human confusion by making clusters clearly distinguishable.

While the bandwidth requirement of a corosync cluster is relatively low, the latency of packages and the package per second (PPS) rate is the limiting factor. Different clusters in the same network can compete with each other for these resources, so it may still make sense to use separate physical network infrastructure for bigger clusters.

Login to the web interface on an existing cluster node. Under Datacenter → Cluster, click the button Join Information at the top. Then, click on the button Copy Information. Alternatively, copy the string from the Information field manually.

Next, login to the web interface on the node you want to add. Under Datacenter → Cluster, click on Join Cluster. Fill in the Information field with the Join Information text you copied earlier. Most settings required for joining the cluster will be filled out automatically. For security reasons, the cluster password has to be entered manually.

After clicking the Join button, the cluster join process will start immediately. After the node joined the cluster its current node certificate will be replaced by one signed from the cluster certificate authority (CA), that means the current session will stop to work after a few seconds. You might then need to force-reload the webinterface and re-login with the cluster credentials.

Now your node should be visible under Datacenter → Cluster.

Login via ssh to the node you want to join into an existing cluster.

For IP-ADDRESS-CLUSTER use the IP or hostname of an existing cluster node. An IP address is recommended (see Link Address Types).

To check the state of the cluster use:

If you only want the list of all nodes use:

When adding a node to a cluster with a separated cluster network you need to use the link0 parameter to set the nodes address on that network:

If you want to use the built-in redundancy of the kronosnet transport layer, also use the link1 parameter.

Using the GUI, you can select the correct interface from the corresponding Link 0 and Link 1 fields in the Cluster Join dialog.

You can also separate a node from a cluster without reinstalling it from scratch. But after removing the node from the cluster it will still have access to the shared storages! This must be resolved before you start removing the node from the cluster. A Proxmox VE cluster cannot share the exact same storage with another cluster, as storage locking doesn’t work over the cluster boundary. Further, it may also lead to VMID conflicts.

Its suggested that you create a new storage where only the node which you want to separate has access. This can be a new export on your NFS or a new Ceph pool, to name a few examples. Its just important that the exact same storage does not gets accessed by multiple clusters. After setting this storage up move all data from the node and its VMs to it. Then you are ready to separate the node from the cluster.

First, stop the corosync and the pve-cluster services on the node:

Start the cluster filesystem again in local mode:

Delete the corosync configuration files:

You can now start the filesystem again as normal service:

The node is now separated from the cluster. You can deleted it from a remaining node of the cluster with:

If the command failed, because the remaining node in the cluster lost quorum when the now separate node exited, you may set the expected votes to 1 as a workaround:

And then repeat the pvecm delnode command.

Now switch back to the separated node, here delete all remaining files left from the old cluster. This ensures that the node can be added to another cluster again without problems.

As the configuration files from the other nodes are still in the cluster filesystem you may want to clean those up too. Remove simply the whole directory recursive from /etc/pve/nodes/NODENAME, but check three times that you used the correct one before deleting it.

This needs a reliable network with latencies under 2 milliseconds (LAN performance) to work properly. The network should not be used heavily by other members, ideally corosync runs on its own network. Do not use a shared network for corosync and storage (except as a potential low-priority fallback in a redundant configuration).

Before setting up a cluster, it is good practice to check if the network is fit for that purpose. To make sure the nodes can connect to each other on the cluster network, you can test the connectivity between them with the ping tool.

If the Proxmox VE firewall is enabled, ACCEPT rules for corosync will automatically be generated - no manual action is required.

When creating a cluster without any parameters the corosync cluster network is generally shared with the Web UI and the VMs and their traffic. Depending on your setup, even storage traffic may get sent over the same network. Its recommended to change that, as corosync is a time critical real time application.

A corosync link address (for backwards compatibility denoted by ringX_addr in corosync.conf) can be specified in two ways:

A separate, static hostname specifically for corosync is recommended, if hostnames are preferred. Also, make sure that every node in the cluster can resolve all hostnames correctly.

Since Proxmox VE 5.1, while supported, hostnames will be resolved at the time of entry. Only the resolved IP is then saved to the configuration.

Nodes that joined the cluster on earlier versions likely still use their unresolved hostname in corosync.conf. It might be a good idea to replace them with IPs or a separate hostname, as mentioned above.

To add a new link to a running configuration, first check how to edit the corosync.conf file.

Then, add a new ringX_addr to every node in the nodelist section. Make sure that your X is the same for every node you add it to, and that it is unique for each node.

Lastly, add a new interface, as shown below, to your totem section, replacing X with your link number chosen above.

Assuming you added a link with number 1, the new configuration file could look like this:

The new link will be enabled as soon as you follow the last steps to edit the corosync.conf file. A restart should not be necessary. You can check that corosync loaded the new link using:

It might be a good idea to test the new link by temporarily disconnecting the old link on one node and making sure that its status remains online while disconnected:

If you see a healthy cluster state, it means that your new link is being used.

The Corosync Quorum Device (QDevice) is a daemon which runs on each cluster node. It provides a configured number of votes to the clusters quorum subsystem based on an external running third-party arbitrator’s decision. Its primary use is to allow a cluster to sustain more node failures than standard quorum rules allow. This can be done safely as the external device can see all nodes and thus choose only one set of nodes to give its vote. This will only be done if said set of nodes can have quorum (again) when receiving the third-party vote.

Currently only QDevice Net is supported as a third-party arbitrator. It is a daemon which provides a vote to a cluster partition if it can reach the partition members over the network. It will give only votes to one partition of a cluster at any time. It’s designed to support multiple clusters and is almost configuration and state free. New clusters are handled dynamically and no configuration file is needed on the host running a QDevice.

The external host has the only requirement that it needs network access to the cluster and a corosync-qnetd package available. We provide such a package for Debian based hosts, other Linux distributions should also have a package available through their respective package manager.

We support QDevices for clusters with an even number of nodes and recommend it for 2 node clusters, if they should provide higher availability. For clusters with an odd node count we discourage the use of QDevices currently. The reason for this, is the difference of the votes the QDevice provides for each cluster type. Even numbered clusters get single additional vote, with this we can only increase availability, i.e. if the QDevice itself fails we are in the same situation as with no QDevice at all.

Now, with an odd numbered cluster size the QDevice provides (N-1) votes — where N corresponds to the cluster node count. This difference makes sense, if we had only one additional vote the cluster can get into a split brain situation. This algorithm would allow that all nodes but one (and naturally the QDevice itself) could fail. There are two drawbacks with this:

If you understand the drawbacks and implications you can decide yourself if you should use this technology in an odd numbered cluster setup.

We recommend to run any daemon which provides votes to corosync-qdevice as an unprivileged user. Proxmox VE and Debian provide a package which is already configured to do so. The traffic between the daemon and the cluster must be encrypted to ensure a safe and secure QDevice integration in Proxmox VE.

First, install the corosync-qnetd package on your external server

and the corosync-qdevice package on all cluster nodes

After that, ensure that all your nodes on the cluster are online.

You can now easily set up your QDevice by running the following command on one of the Proxmox VE nodes:

The SSH key from the cluster will be automatically copied to the QDevice.

After you enter the password and all the steps are successfully completed, you will see "Done". You can check the status now:

which means the QDevice is set up.

Editing the corosync.conf file is not always very straightforward. There are two on each cluster node, one in /etc/pve/corosync.conf and the other in /etc/corosync/corosync.conf. Editing the one in our cluster file system will propagate the changes to the local one, but not vice versa.

The configuration will get updated automatically as soon as the file changes. This means changes which can be integrated in a running corosync will take effect immediately. So you should always make a copy and edit that instead, to avoid triggering some unwanted changes by an in-between safe.

Then open the config file with your favorite editor, nano and vim.tiny are preinstalled on any Proxmox VE node for example.

After making the necessary changes create another copy of the current working configuration file. This serves as a backup if the new configuration fails to apply or makes problems in other ways.

Then move the new configuration file over the old one:

You may check with the commands

If the change could be applied automatically. If not you may have to restart the corosync service via:

On errors check the troubleshooting section below.

The migration type defines if the migration data should be sent over an encrypted (secure) channel or an unencrypted (insecure) one. Setting the migration type to insecure means that the RAM content of a virtual guest gets also transferred unencrypted, which can lead to information disclosure of critical data from inside the guest (for example passwords or encryption keys).

Therefore, we strongly recommend using the secure channel if you do not have full control over the network and can not guarantee that no one is eavesdropping on it.

Encryption requires a lot of computing power, so this setting is often changed to "unsafe" to achieve better performance. The impact on modern systems is lower because they implement AES encryption in hardware. The performance impact is particularly evident in fast networks where you can transfer 10 Gbps or more.

By default, Proxmox VE uses the network in which cluster communication takes place to send the migration traffic. This is not optimal because sensitive cluster traffic can be disrupted and this network may not have the best bandwidth available on the node.

Setting the migration network parameter allows the use of a dedicated network for the entire migration traffic. In addition to the memory, this also affects the storage traffic for offline migrations.

The migration network is set as a network in the CIDR notation. This has the advantage that you do not have to set individual IP addresses for each node. Proxmox VE can determine the real address on the destination node from the network specified in the CIDR form. To enable this, the network must be specified so that each node has one, but only one IP in the respective network.