Cluster Manager

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The Proxmox VE cluster manager pvecm is a tool to create a group of physical servers. Such a group is called a cluster. We use the Corosync Cluster Engine for reliable group communication, and such clusters can consist of up to 32 physical nodes (probably more, dependent on network latency).

pvecm can be used to create a new cluster, join nodes to a cluster, leave the cluster, get status information and do various other cluster related tasks. The Proxmox Cluster File System (“pmxcfs”) is used to transparently distribute the cluster configuration to all cluster nodes.

Grouping nodes into a cluster has the following advantages:

  • Centralized, web based management

  • Multi-master clusters: each node can do all management task

  • pmxcfs: database-driven file system for storing configuration files, replicated in real-time on all nodes using corosync.

  • Easy migration of virtual machines and containers between physical hosts

  • Fast deployment

  • Cluster-wide services like firewall and HA

Requirements

  • All nodes must be in the same network as corosync uses IP Multicast to communicate between nodes (also see Corosync Cluster Engine). Corosync uses UDP ports 5404 and 5405 for cluster communication.

    Note Some switches do not support IP multicast by default and must be manually enabled first.
  • Date and time have to be synchronized.

  • SSH tunnel on TCP port 22 between nodes is used.

  • If you are interested in High Availability, you need to have at least three nodes for reliable quorum. All nodes should have the same version.

  • We recommend a dedicated NIC for the cluster traffic, especially if you use shared storage.

Note It is not possible to mix Proxmox VE 3.x and earlier with Proxmox VE 4.0 cluster nodes.

Preparing Nodes

First, install Proxmox VE on all nodes. Make sure that each 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, so you need to login via ssh.

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.

hp1# pvecm create YOUR-CLUSTER-NAME
Caution The cluster name is used to compute the default multicast address. Please use unique cluster names if you run more than one cluster inside your network.

To check the state of your cluster use:

hp1# pvecm status

Adding Nodes to the Cluster

Login via ssh to the node you want to add.

hp2# pvecm add IP-ADDRESS-CLUSTER

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

Caution A new node cannot hold any VMs, because you would get conflicts about identical VM IDs. Also, all existing configuration in /etc/pve is overwritten when you join a new node to the cluster. To workaround, use vzdump to backup and restore to a different VMID after adding the node to the cluster.

To check the state of cluster:

# pvecm status
Cluster status after adding 4 nodes
hp2# pvecm status
Quorum information
~~~~~~~~~~~~~~~~~~
Date:             Mon Apr 20 12:30:13 2015
Quorum provider:  corosync_votequorum
Nodes:            4
Node ID:          0x00000001
Ring ID:          1928
Quorate:          Yes

Votequorum information
~~~~~~~~~~~~~~~~~~~~~~
Expected votes:   4
Highest expected: 4
Total votes:      4
Quorum:           2
Flags:            Quorate

Membership information
~~~~~~~~~~~~~~~~~~~~~~
    Nodeid      Votes Name
0x00000001          1 192.168.15.91
0x00000002          1 192.168.15.92 (local)
0x00000003          1 192.168.15.93
0x00000004          1 192.168.15.94

If you only want the list of all nodes use:

# pvecm nodes
List nodes in a cluster
hp2# pvecm nodes

Membership information
~~~~~~~~~~~~~~~~~~~~~~
    Nodeid      Votes Name
         1          1 hp1
         2          1 hp2 (local)
         3          1 hp3
         4          1 hp4

Adding Nodes With Separated Cluster Network

When adding a node to a cluster with a separated cluster network you need to use the ringX_addr parameters to set the nodes address on those networks:

pvecm add IP-ADDRESS-CLUSTER -ring0_addr IP-ADDRESS-RING0

If you want to use the Redundant Ring Protocol you will also want to pass the ring1_addr parameter.

Remove a Cluster Node

Caution Read carefully the procedure before proceeding, as it could not be what you want or need.

Move all virtual machines from the node. Make sure you have no local data or 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 node ID:

hp1# pvecm status

Quorum information
~~~~~~~~~~~~~~~~~~
Date:             Mon Apr 20 12:30:13 2015
Quorum provider:  corosync_votequorum
Nodes:            4
Node ID:          0x00000001
Ring ID:          1928
Quorate:          Yes

Votequorum information
~~~~~~~~~~~~~~~~~~~~~~
Expected votes:   4
Highest expected: 4
Total votes:      4
Quorum:           2
Flags:            Quorate

Membership information
~~~~~~~~~~~~~~~~~~~~~~
    Nodeid      Votes Name
0x00000001          1 192.168.15.91 (local)
0x00000002          1 192.168.15.92
0x00000003          1 192.168.15.93
0x00000004          1 192.168.15.94
Important at this point you must power off the node to be removed and make sure that it will not power on again (in the network) as it is.
hp1# pvecm nodes

Membership information
~~~~~~~~~~~~~~~~~~~~~~
    Nodeid      Votes Name
         1          1 hp1 (local)
         2          1 hp2
         3          1 hp3
         4          1 hp4

Log in to one remaining node via ssh. Issue the delete command (here deleting node hp4):

hp1# pvecm delnode hp4

If the operation succeeds no output is returned, just check the node list again with pvecm nodes or pvecm status. You should see something like:

hp1# pvecm status

Quorum information
~~~~~~~~~~~~~~~~~~
Date:             Mon Apr 20 12:44:28 2015
Quorum provider:  corosync_votequorum
Nodes:            3
Node ID:          0x00000001
Ring ID:          1992
Quorate:          Yes

Votequorum information
~~~~~~~~~~~~~~~~~~~~~~
Expected votes:   3
Highest expected: 3
Total votes:      3
Quorum:           3
Flags:            Quorate

Membership information
~~~~~~~~~~~~~~~~~~~~~~
    Nodeid      Votes Name
0x00000001          1 192.168.15.90 (local)
0x00000002          1 192.168.15.91
0x00000003          1 192.168.15.92
Important as said above, it is very important to power off the node before removal, and make sure that it will never power on again (in the existing cluster network) as it is.

If you power on the node as it is, your cluster will be screwed up and it could be difficult to restore a clean cluster state.

If, for whatever reason, you want that this server joins the same cluster again, you have to

  • reinstall Proxmox VE on it from scratch

  • then join it, as explained in the previous section.

Separate A Node Without Reinstalling

Caution This is not the recommended method, proceed with caution. Use the above mentioned method if you’re unsure.

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 it leads 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 an 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.

Warning Ensure all shared resources are cleanly separated! You will run into conflicts and problems else.

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

systemctl stop pve-cluster
systemctl stop corosync

Start the cluster filesystem again in local mode:

pmxcfs -l

Delete the corosync configuration files:

rm /etc/pve/corosync.conf
rm /etc/corosync/*

You can now start the filesystem again as normal service:

killall pmxcfs
systemctl start pve-cluster

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

pvecm delnode oldnode

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:

pvecm expected 1

And the 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.

rm /var/lib/corosync/*

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.

Caution The nodes SSH keys are still in the authorized_key file, this means the nodes can still connect to each other with public key authentication. This should be fixed by removing the respective keys from the /etc/pve/priv/authorized_keys file.

Quorum

Proxmox VE use a quorum-based technique to provide a consistent state among all cluster nodes.

A quorum is the minimum number of votes that a distributed transaction has to obtain in order to be allowed to perform an operation in a distributed system.

Quorum (distributed computing)
— from Wikipedia

In case of network partitioning, state changes requires that a majority of nodes are online. The cluster switches to read-only mode if it loses quorum.

Note Proxmox VE assigns a single vote to each node by default.

Cluster Network

The cluster network is the core of a cluster. All messages sent over it have to be delivered reliable to all nodes in their respective order. In Proxmox VE this part is done by corosync, an implementation of a high performance low overhead high availability development toolkit. It serves our decentralized configuration file system (pmxcfs).

Network Requirements

This needs a reliable network with latencies under 2 milliseconds (LAN performance) to work properly. While corosync can also use unicast for communication between nodes its highly recommended to have a multicast capable network. The network should not be used heavily by other members, ideally corosync runs on its own network. never share it with network where storage communicates too.

Before setting up a cluster it is good practice to check if the network is fit for that purpose.

  • Ensure that all nodes are in the same subnet. This must only be true for the network interfaces used for cluster communication (corosync).

  • Ensure all nodes can reach each other over those interfaces, using ping is enough for a basic test.

  • Ensure that multicast works in general and a high package rates. This can be done with the omping tool. The final "%loss" number should be < 1%.

omping -c 10000 -i 0.001 -F -q NODE1-IP NODE2-IP ...
  • Ensure that multicast communication works over an extended period of time. This covers up problems where IGMP snooping is activated on the network but no multicast querier is active. This test has a duration of around 10 minutes.

omping -c 600 -i 1 -q NODE1-IP NODE2-IP ...

Your network is not ready for clustering if any of these test fails. Recheck your network configuration. Especially switches are notorious for having multicast disabled by default or IGMP snooping enabled with no IGMP querier active.

In smaller cluster its also an option to use unicast if you really cannot get multicast to work.

Separate Cluster Network

When creating a cluster without any parameters the cluster network is generally shared with the Web UI and the VMs and its 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.

Setting Up A New Network

First you have to setup a new network interface. It should be on a physical separate network. Ensure that your network fulfills the cluster network requirements.

Separate On Cluster Creation

This is possible through the ring0_addr and bindnet0_addr parameter of the pvecm create command used for creating a new cluster.

If you have setup a additional NIC with a static address on 10.10.10.1/25 and want to send and receive all cluster communication over this interface you would execute:

pvecm create test --ring0_addr 10.10.10.1 --bindnet0_addr 10.10.10.0

To check if everything is working properly execute:

systemctl status corosync

Separate After Cluster Creation

You can do this also if you have already created a cluster and want to switch its communication to another network, without rebuilding the whole cluster. This change may lead to short durations of quorum loss in the cluster, as nodes have to restart corosync and come up one after the other on the new network.

Check how to edit the corosync.conf file first. The open it and you should see a file similar to:

logging {
  debug: off
  to_syslog: yes
}

nodelist {

  node {
    name: due
    nodeid: 2
    quorum_votes: 1
    ring0_addr: due
  }

  node {
    name: tre
    nodeid: 3
    quorum_votes: 1
    ring0_addr: tre
  }

  node {
    name: uno
    nodeid: 1
    quorum_votes: 1
    ring0_addr: uno
  }

}

quorum {
  provider: corosync_votequorum
}

totem {
  cluster_name: thomas-testcluster
  config_version: 3
  ip_version: ipv4
  secauth: on
  version: 2
  interface {
    bindnetaddr: 192.168.30.50
    ringnumber: 0
  }

}

The first you want to do is add the name properties in the node entries if you do not see them already. Those must match the node name.

Then replace the address from the ring0_addr properties with the new addresses. You may use plain IP addresses or also hostnames here. If you use hostnames ensure that they are resolvable from all nodes.

In my example I want to switch my cluster communication to the 10.10.10.1/25 network. So I replace all ring0_addr respectively. I also set the bindetaddr in the totem section of the config to an address of the new network. It can be any address from the subnet configured on the new network interface.

After you increased the config_version property the new configuration file should look like:

logging {
  debug: off
  to_syslog: yes
}

nodelist {

  node {
    name: due
    nodeid: 2
    quorum_votes: 1
    ring0_addr: 10.10.10.2
  }

  node {
    name: tre
    nodeid: 3
    quorum_votes: 1
    ring0_addr: 10.10.10.3
  }

  node {
    name: uno
    nodeid: 1
    quorum_votes: 1
    ring0_addr: 10.10.10.1
  }

}

quorum {
  provider: corosync_votequorum
}

totem {
  cluster_name: thomas-testcluster
  config_version: 4
  ip_version: ipv4
  secauth: on
  version: 2
  interface {
    bindnetaddr: 10.10.10.1
    ringnumber: 0
  }

}

Now after a final check whether all changed information is correct we save it and see again the edit corosync.conf file section to learn how to bring it in effect.

As our change cannot be enforced live from corosync we have to do an restart.

On a single node execute:

systemctl restart corosync

Now check if everything is fine:

systemctl status corosync

If corosync runs again correct restart corosync also on all other nodes. They will then join the cluster membership one by one on the new network.

Redundant Ring Protocol

To avoid a single point of failure you should implement counter measurements. This can be on the hardware and operating system level through network bonding.

Corosync itself offers also a possibility to add redundancy through the so called Redundant Ring Protocol. This protocol allows running a second totem ring on another network, this network should be physically separated from the other rings network to actually increase availability.

RRP On Cluster Creation

The pvecm create command provides the additional parameters bindnetX_addr, ringX_addr and rrp_mode, can be used for RRP configuration.

Note See the glossary if you do not know what each parameter means.

So if you have two networks, one on the 10.10.10.1/24 and the other on the 10.10.20.1/24 subnet you would execute:

pvecm create CLUSTERNAME -bindnet0_addr 10.10.10.1 -ring0_addr 10.10.10.1 \
-bindnet1_addr 10.10.20.1 -ring1_addr 10.10.20.1

RRP On A Created Cluster

When enabling an already running cluster to use RRP you will take similar steps as describe in separating the cluster network. You just do it on another ring.

First add a new interface subsection in the totem section, set its ringnumber property to 1. Set the interfaces bindnetaddr property to an address of the subnet you have configured for your new ring. Further set the rrp_mode to passive, this is the only stable mode.

Then add to each node entry in the nodelist section its new ring1_addr property with the nodes additional ring address.

So if you have two networks, one on the 10.10.10.1/24 and the other on the 10.10.20.1/24 subnet, the final configuration file should look like:

totem {
  cluster_name: tweak
  config_version: 9
  ip_version: ipv4
  rrp_mode: passive
  secauth: on
  version: 2
  interface {
    bindnetaddr: 10.10.10.1
    ringnumber: 0
  }
  interface {
    bindnetaddr: 10.10.20.1
    ringnumber: 1
  }
}

nodelist {
  node {
    name: pvecm1
    nodeid: 1
    quorum_votes: 1
    ring0_addr: 10.10.10.1
    ring1_addr: 10.10.20.1
  }

 node {
    name: pvecm2
    nodeid: 2
    quorum_votes: 1
    ring0_addr: 10.10.10.2
    ring1_addr: 10.10.20.2
  }

  [...] # other cluster nodes here
}

[...] # other remaining config sections here

Bring it in effect like described in the edit the corosync.conf file section.

This is a change which cannot take live in effect and needs at least a restart of corosync. Recommended is a restart of the whole cluster.

If you cannot reboot the whole cluster ensure no High Availability services are configured and the stop the corosync service on all nodes. After corosync is stopped on all nodes start it one after the other again.

Corosync Configuration

The /ect/pve/corosync.conf file plays a central role in Proxmox VE cluster. It controls the cluster member ship and its network. For reading more about it check the corosync.conf man page:

man corosync.conf

For node membership you should always use the pvecm tool provided by Proxmox VE. You may have to edit the configuration file manually for other changes. Here are a few best practice tips for doing this.

Edit corosync.conf

Editing the corosync.conf file can be not always straight forward. There are two on each cluster, 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 instantly effect. So you should always make a copy and edit that instead, to avoid triggering some unwanted changes by an in between safe.

cp /etc/pve/corosync.conf /etc/pve/corosync.conf.new

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

Note Always increment the config_version number on configuration changes, omitting this can lead to problems.

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.

cp /etc/pve/corosync.conf /etc/pve/corosync.conf.bak

Then move the new configuration file over the old one:

mv /etc/pve/corosync.conf.new /etc/pve/corosync.conf

You may check with the commands

systemctl status corosync
journalctl -b -u corosync

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

systemctl restart corosync

On errors check the troubleshooting section below.

Troubleshooting

Issue: quorum.expected_votes must be configured

When corosync starts to fail and you get the following message in the system log:

[...]
corosync[1647]:  [QUORUM] Quorum provider: corosync_votequorum failed to initialize.
corosync[1647]:  [SERV  ] Service engine 'corosync_quorum' failed to load for reason
    'configuration error: nodelist or quorum.expected_votes must be configured!'
[...]

It means that the hostname you set for corosync ringX_addr in the configuration could not be resolved.

Write Configuration When Not Quorate

If you need to change /etc/pve/corosync.conf on an node with no quorum, and you know what you do, use:

pvecm expected 1

This sets the expected vote count to 1 and makes the cluster quorate. You can now fix your configuration, or revert it back to the last working backup.

This is not enough if corosync cannot start anymore. Here its best to edit the local copy of the corosync configuration in /etc/corosync/corosync.conf so that corosync can start again. Ensure that on all nodes this configuration has the same content to avoid split brains. If you are not sure what went wrong it’s best to ask the Proxmox Community to help you.

Corosync Configuration Glossary

ringX_addr

This names the different ring addresses for the corosync totem rings used for the cluster communication.

bindnetaddr

Defines to which interface the ring should bind to. It may be any address of the subnet configured on the interface we want to use. In general its the recommended to just use an address a node uses on this interface.

rrp_mode

Specifies the mode of the redundant ring protocol and may be passive, active or none. Note that use of active is highly experimental and not official supported. Passive is the preferred mode, it may double the cluster communication throughput and increases availability.

Cluster Cold Start

It is obvious that a cluster is not quorate when all nodes are offline. This is a common case after a power failure.

Note It is always a good idea to use an uninterruptible power supply (“UPS”, also called “battery backup”) to avoid this state, especially if you want HA.

On node startup, service pve-manager is started and waits for quorum. Once quorate, it starts all guests which have the onboot flag set.

When you turn on nodes, or when power comes back after power failure, it is likely that some nodes boots faster than others. Please keep in mind that guest startup is delayed until you reach quorum.

Guest Migration

Migrating virtual guests to other nodes is a useful feature in a cluster. There are settings to control the behavior of such migrations. This can be done via the configuration file datacenter.cfg or for a specific migration via API or command line parameters.

Migration Type

The migration type defines if the migration data should be sent over a 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 transfered 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 to it.

Note Storage migration does not follow this setting. Currently, it always sends the storage content over a secure channel.

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.

Migration Network

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.

Example

We assume that we have a three-node setup with three separate networks. One for public communication with the Internet, one for cluster communication and a very fast one, which we want to use as a dedicated network for migration.

A network configuration for such a setup might look as follows:

iface eth0 inet manual

# public network
auto vmbr0
iface vmbr0 inet static
    address 192.X.Y.57
    netmask 255.255.250.0
    gateway 192.X.Y.1
    bridge_ports eth0
    bridge_stp off
    bridge_fd 0

# cluster network
auto eth1
iface eth1 inet static
    address  10.1.1.1
    netmask  255.255.255.0

# fast network
auto eth2
iface eth2 inet static
    address  10.1.2.1
    netmask  255.255.255.0

Here, we will use the network 10.1.2.0/24 as a migration network. For a single migration, you can do this using the migration_network parameter of the command line tool:

# qm migrate 106 tre --online --migration_network 10.1.2.0/24

To configure this as the default network for all migrations in the cluster, set the migration property of the /etc/pve/datacenter.cfg file:

# use dedicated migration network
migration: secure,network=10.1.2.0/24
Note The migration type must always be set when the migration network gets set in /etc/pve/datacenter.cfg.