Cluster Manager: Difference between revisions

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physical servers. Such a group is called a cluster. We use the
physical servers. Such a group is called a cluster. We use the
Corosync Cluster Engine for reliable group
Corosync Cluster Engine for reliable group
communication, and such clusters can consist of up to 32 physical nodes
communication. There’s no explicit limit for the number of nodes in a cluster.
(probably more, dependent on network latency).
In practice, the actual possible node count may be limited by the host and
network performance. Currently (2021), there are reports of clusters (using
high-end enterprise hardware) with over 50 nodes in production.
pvecm can be used to create a new cluster, join nodes to a cluster,
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
leave the cluster, get status information, and do various other cluster-related
related tasks. The Proxmox Cluster File System (“pmxcfs”)
tasks. The Proxmox Cluster File System (“pmxcfs”)
is used to transparently distribute the cluster configuration to all cluster
is used to transparently distribute the cluster configuration to all cluster
nodes.
nodes.
Grouping nodes into a cluster has the following advantages:
Grouping nodes into a cluster has the following advantages:
Centralized, web based management
Centralized, web-based management
Multi-master clusters: each node can do all management task
Multi-master clusters: each node can do all management tasks
pmxcfs: database-driven file system for storing configuration files,
Use of pmxcfs, a database-driven file system, for storing configuration
replicated in real-time on all nodes using corosync.
  files, replicated in real-time on all nodes using corosync
Easy migration of virtual machines and containers between physical
Easy migration of virtual machines and containers between physical
   hosts
   hosts
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Cluster-wide services like firewall and HA
Cluster-wide services like firewall and HA
Requirements
Requirements
All nodes must be in the same network as corosync uses IP Multicast
All nodes must be able to connect to each other via UDP ports 5405-5412
to communicate between nodes (also see
  for corosync to work.
Corosync Cluster Engine). Corosync uses UDP
Date and time must be synchronized.
  ports 5404 and 5405 for cluster communication.
An SSH tunnel on TCP port 22 between nodes is required.
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
If you are interested in High Availability, you need to have at
   least three nodes for reliable quorum. All nodes should have the
   least three nodes for reliable quorum. All nodes should have the
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We recommend a dedicated NIC for the cluster traffic, especially if
We recommend a dedicated NIC for the cluster traffic, especially if
   you use shared storage.
   you use shared storage.
It is not possible to mix Proxmox VE 3.x and earlier with
The root password of a cluster node is required for adding nodes.
Proxmox VE 4.0 cluster nodes.
Online migration of virtual machines is only supported when nodes have CPUs
  from the same vendor. It might work otherwise, but this is never guaranteed.
It is not possible to mix Proxmox VE 3.x and earlier with Proxmox VE 4.X cluster
nodes.
While it’s possible to mix Proxmox VE 4.4 and Proxmox VE 5.0 nodes, doing so is
not supported as a production configuration and should only be done temporarily,
during an upgrade of the whole cluster from one major version to another.
Running a cluster of Proxmox VE 6.x with earlier versions is not possible. The
cluster protocol (corosync) between Proxmox VE 6.x and earlier versions changed
fundamentally. The corosync 3 packages for Proxmox VE 5.4 are only intended for the
upgrade procedure to Proxmox VE 6.0.
Preparing Nodes
Preparing Nodes
First, install Proxmox VE on all nodes. Make sure that each node is
First, install Proxmox VE on all nodes. Make sure that each node is
installed with the final hostname and IP configuration. Changing the
installed with the final hostname and IP configuration. Changing the
hostname and IP is not possible after cluster creation.
hostname and IP is not possible after cluster creation.
Currently the cluster creation has to be done on the console, so you
While it’s common to reference all node names and their IPs in /etc/hosts (or
need to login via ssh.
make their names resolvable through other means), this is not necessary for a
Create the Cluster
cluster to work. It may be useful however, as you can then connect from one node
Login via ssh to the first Proxmox VE node. Use a unique name for your cluster.
to another via SSH, using the easier to remember node name (see also
This name cannot be changed later.
Link Address Types). Note that we always
hp1# pvecm create YOUR-CLUSTER-NAME
recommend referencing nodes by their IP addresses in the cluster configuration.
The cluster name is used to compute the default multicast
Create a Cluster
address. Please use unique cluster names if you run more than one
You can either create a cluster on the console (login via ssh), or through
cluster inside your network.
the API using the Proxmox VE web interface (Datacenter → Cluster).
To check the state of your cluster use:
Use a unique name for your cluster. This name cannot be changed later.
hp1# pvecm status
The cluster name follows the same rules as node names.
Create via Web GUI
Under Datacenter → Cluster, click on Create Cluster. Enter the cluster
name and select a network connection from the drop-down list to serve as the
main cluster network (Link 0). It defaults to the IP resolved via the node’s
hostname.
As of Proxmox VE 6.2, up to 8 fallback links can be added to a cluster. To add a
redundant link, click the Add button and select a link number and IP address
from the respective fields. Prior to Proxmox VE 6.2, 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).
Ensure that the network selected for cluster communication is not used for
any high traffic purposes, like network storage or live-migration.
While the cluster network itself produces small amounts of data, it is very
sensitive to latency. Check out full
cluster network requirements.
Create via the Command Line
Login via ssh to the first Proxmox VE node and run the following command:
hp1# pvecm create CLUSTERNAME
To check the state of the new cluster use:
hp1# pvecm status
Multiple Clusters in the Same Network
It is possible to create multiple clusters in the same physical or logical
network. In this case, each cluster must have a unique name to avoid possible
clashes in the cluster communication stack. Furthermore, this 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.
Adding Nodes to the Cluster
Adding Nodes to the Cluster
Login via ssh to the node you want to add.
All existing configuration in /etc/pve is overwritten when joining a
hp2# pvecm add IP-ADDRESS-CLUSTER
cluster. In particular, a joining node cannot hold any guests, since guest IDs
For IP-ADDRESS-CLUSTER use the IP from an existing cluster node.
could otherwise conflict, and the node will inherit the cluster’s storage
A new node cannot hold any VMs, because you would get
configuration. To join a node with existing guest, as a workaround, you can
conflicts about identical VM IDs. Also, all existing configuration in
create a backup of each guest (using vzdump) and restore it under a different
/etc/pve is overwritten when you join a new node to the cluster. To
ID after joining. If the node’s storage layout differs, you will need to re-add
workaround, use vzdump to backup and restore to a different VMID after
the node’s storages, and adapt each storage’s node restriction to reflect on
adding the node to the cluster.
which nodes the storage is actually available.
To check the state of cluster:
Join Node to Cluster via GUI
# pvecm status
Log in to the web interface on an existing cluster node. Under Datacenter →
Cluster, click the Join Information button at the top. Then, click on the
button Copy Information. Alternatively, copy the string from the Information
field manually.
Next, log in 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.
To enter all required data manually, you can disable the Assisted Join
checkbox.
After clicking the Join button, the cluster join process will start
immediately. After the node has joined the cluster, its current node certificate
will be replaced by one signed from the cluster certificate authority (CA).
This means that the current session will stop working after a few seconds. You
then might need to force-reload the web interface and log in again with the
cluster credentials.
Now your node should be visible under Datacenter → Cluster.
Join Node to Cluster via Command Line
Log in to the node you want to join into an existing cluster via ssh.
# pvecm add IP-ADDRESS-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:
# pvecm status
Cluster status after adding 4 nodes
Cluster status after adding 4 nodes
hp2# pvecm status
# pvecm status
Cluster information
~~~~~~~~~~~~~~~~~~~
Name:            prod-central
Config Version:  3
Transport:        knet
Secure auth:      on
Quorum information
Quorum information
~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~
Date:            Mon Apr 20 12:30:13 2015
Date:            Tue Sep 14 11:06:47 2021
Quorum provider:  corosync_votequorum
Quorum provider:  corosync_votequorum
Nodes:            4
Nodes:            4
Node ID:          0x00000001
Node ID:          0x00000001
Ring ID:          1928
Ring ID:          1.1a8
Quorate:          Yes
Quorate:          Yes
Votequorum information
Votequorum information
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Highest expected: 4
Highest expected: 4
Total votes:      4
Total votes:      4
Quorum:          2
Quorum:          3
Flags:            Quorate
Flags:            Quorate
Membership information
Membership information
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0x00000003          1 192.168.15.93
0x00000003          1 192.168.15.93
0x00000004          1 192.168.15.94
0x00000004          1 192.168.15.94
If you only want the list of all nodes use:
If you only want a list of all nodes, use:
# pvecm nodes
# pvecm nodes
List nodes in a cluster
List nodes in a cluster
hp2# pvecm nodes
# pvecm nodes
Membership information
Membership information
~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~
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         3          1 hp3
         3          1 hp3
         4          1 hp4
         4          1 hp4
Adding Nodes With Separated Cluster Network
Adding Nodes with Separated Cluster Network
When adding a node to a cluster with a separated cluster network you need to
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:
use the link0 parameter to set the nodes address on that network:
pvecm add IP-ADDRESS-CLUSTER -ring0_addr IP-ADDRESS-RING0
# pvecm add IP-ADDRESS-CLUSTER --link0 LOCAL-IP-ADDRESS-LINK0
If you want to use the Redundant Ring Protocol you will also want to pass the
If you want to use the built-in redundancy of the
ring1_addr parameter.
Kronosnet transport layer, also use the link1 parameter.
Using the GUI, you can select the correct interface from the corresponding
Link X fields in the Cluster Join dialog.
Remove a Cluster Node
Remove a Cluster Node
Read carefully the procedure before proceeding, as it could
Read the procedure carefully before proceeding, as it may
not be what you want or need.
not be what you want or need.
Move all virtual machines from the node. Make sure you have no local
Move all virtual machines from the node. Ensure that you have made copies of any
data or backups you want to keep, or save them accordingly.
local data or backups that you want to keep. In addition, make sure to remove
Log in to one remaining node via ssh. Issue a pvecm nodes command to
any scheduled replication jobs to the node to be removed.
identify the node ID:
Failure to remove replication jobs to a node before removing said node
hp1# pvecm status
will result in the replication job becoming irremovable. Especially note that
Quorum information
replication automatically switches direction if a replicated VM is migrated, so
~~~~~~~~~~~~~~~~~~
by migrating a replicated VM from a node to be deleted, replication jobs will be
Date:            Mon Apr 20 12:30:13 2015
set up to that node automatically.
Quorum provider:  corosync_votequorum
In the following example, we will remove the node hp4 from the cluster.
Nodes:            4
Log in to a different cluster node (not hp4), and issue a pvecm nodes
Node ID:          0x00000001
command to identify the node ID to remove:
Ring ID:          1928
hp1# pvecm nodes
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
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
Membership information
~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~
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         3          1 hp3
         3          1 hp3
         4          1 hp4
         4          1 hp4
Log in to one remaining node via ssh. Issue the delete command (here
At this point, you must power off hp4 and ensure that it will not power on
deleting node hp4):
again (in the network) with its current configuration.
hp1# pvecm delnode hp4
As mentioned above, it is critical to power off the node
If the operation succeeds no output is returned, just check the node
before removal, and make sure that it will not power on again
list again with pvecm nodes or pvecm status. You should see
(in the existing cluster network) with its current configuration.
something like:
If you power on the node as it is, the cluster could end up broken,
and it could be difficult to restore it to a functioning state.
After powering off the node hp4, we can safely remove it from the cluster.
hp1# pvecm delnode hp4
Killing node 4
At this point, it is possible that you will receive an error message
stating Could not kill node (error = CS_ERR_NOT_EXIST). This does not
signify an actual failure in the deletion of the node, but rather a failure in
corosync trying to kill an offline node. Thus, it can be safely ignored.
Use pvecm nodes or pvecm status to check the node list again. It should
look something like:
hp1# pvecm status
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
Votequorum information
~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~
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Highest expected: 3
Highest expected: 3
Total votes:      3
Total votes:      3
Quorum:          3
Quorum:          2
Flags:            Quorate
Flags:            Quorate
Membership information
Membership information
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0x00000002          1 192.168.15.91
0x00000002          1 192.168.15.91
0x00000003          1 192.168.15.92
0x00000003          1 192.168.15.92
as said above, it is very important to power off the node
If, for whatever reason, you want this server to join the same cluster again,
before removal, and make sure that it will never power on again
you have to:
(in the existing cluster network) as it is.
do a fresh install of Proxmox VE on it,
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.
then join it, as explained in the previous section.
Separate A Node Without Reinstalling
The configuration files for the removed node will still reside in
/etc/pve/nodes/hp4. Recover any configuration you still need and remove the
directory afterwards.
After removal of the node, its SSH fingerprint will still reside in the
known_hosts of the other nodes. If you receive an SSH error after rejoining
a node with the same IP or hostname, run pvecm updatecerts once on the
re-added node to update its fingerprint cluster wide.
Separate a Node Without Reinstalling
This is not the recommended method, proceed with caution. Use the
This is not the recommended method, proceed with caution. Use the
above mentioned method if you’re unsure.
previous method if you’re unsure.
You can also separate a node from a cluster without reinstalling it from
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
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
access to any shared storage. This must be resolved before you start removing
the node from the cluster. A Proxmox VE cluster cannot share the exact same
the node from the cluster. A Proxmox VE cluster cannot share the exact same
storage with another cluster, as it leads to VMID conflicts.
storage with another cluster, as storage locking doesn’t work over the cluster
Its suggested that you create a new storage where only the node which you want
boundary. Furthermore, it may also lead to VMID conflicts.
to separate has access. This can be an new export on your NFS or a new Ceph
It’s suggested that you create a new storage, where only the node which you want
pool, to name a few examples. Its just important that the exact same storage
to separate has access. This can be a new export on your NFS or a new Ceph
does not gets accessed by multiple clusters. After setting this storage up move
pool, to name a few examples. It’s just important that the exact same storage
all data from the node and its VMs to it. Then you are ready to separate the
does not get accessed by multiple clusters. After setting up this storage, move
all data and VMs from the node to it. Then you are ready to separate the
node from the cluster.
node from the cluster.
Ensure all shared resources are cleanly separated! You will run into
Ensure that all shared resources are cleanly separated! Otherwise you
conflicts and problems else.
will run into conflicts and problems.
First stop the corosync and the pve-cluster services on the node:
First, stop the corosync and pve-cluster services on the node:
systemctl stop pve-cluster
systemctl stop pve-cluster
systemctl stop corosync
systemctl stop corosync
Start the cluster filesystem again in local mode:
Start the cluster file system again in local mode:
pmxcfs -l
pmxcfs -l
Delete the corosync configuration files:
Delete the corosync configuration files:
rm /etc/pve/corosync.conf
rm /etc/pve/corosync.conf
rm /etc/corosync/*
rm -r /etc/corosync/*
You can now start the filesystem again as normal service:
You can now start the file system again as a normal service:
killall pmxcfs
killall pmxcfs
systemctl start pve-cluster
systemctl start pve-cluster
The node is now separated from the cluster. You can deleted it from a remaining
The node is now separated from the cluster. You can deleted it from any
node of the cluster with:
remaining node of the cluster with:
pvecm delnode oldnode
pvecm delnode oldnode
If the command failed, because the remaining node in the cluster lost quorum
If the command fails due to a loss of quorum in the remaining node, you can set
when the now separate node exited, you may set the expected votes to 1 as a workaround:
the expected votes to 1 as a workaround:
pvecm expected 1
pvecm expected 1
And the repeat the pvecm delnode command.
And then repeat the pvecm delnode command.
Now switch back to the separated node, here delete all remaining files left
Now switch back to the separated node and delete all the remaining cluster
from the old cluster. This ensures that the node can be added to another
files on it. This ensures that the node can be added to another cluster again
cluster again without problems.
without problems.
rm /var/lib/corosync/*
rm /var/lib/corosync/*
As the configuration files from the other nodes are still in the cluster
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
file system, you may want to clean those up too. After making absolutely sure
directory recursive from /etc/pve/nodes/NODENAME, but check three times that
that you have the correct node name, you can simply remove the entire
you used the correct one before deleting it.
directory recursively from /etc/pve/nodes/NODENAME.
The nodes SSH keys are still in the authorized_key file, this means
The node’s SSH keys will remain in the authorized_key file. This
the nodes can still connect to each other with public key authentication. This
means that the nodes can still connect to each other with public key
should be fixed by removing the respective keys from the
authentication. You should fix this by removing the respective keys from the
/etc/pve/priv/authorized_keys file.
/etc/pve/priv/authorized_keys file.
Quorum
Quorum
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distributed system.
distributed system.
Quorum (distributed computing)
Quorum (distributed computing)
from Wikipedia
— from Wikipedia
In case of network partitioning, state changes requires that a
In case of network partitioning, state changes requires that a
majority of nodes are online. The cluster switches to read-only mode
majority of nodes are online. The cluster switches to read-only mode
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Cluster Network
Cluster Network
The cluster network is the core of a cluster. All messages sent over it have to
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
be delivered reliably to all nodes in their respective order. In Proxmox VE this
part is done by corosync, an implementation of a high performance low overhead
part is done by corosync, an implementation of a high performance, low overhead,
high availability development toolkit. It serves our decentralized
high availability development toolkit. It serves our decentralized configuration
configuration file system (pmxcfs).
file system (pmxcfs).
Network Requirements
Network Requirements
This needs a reliable network with latencies under 2 milliseconds (LAN
The Proxmox VE cluster stack requires a reliable network with latencies under 5
performance) to work properly. While corosync can also use unicast for
milliseconds (LAN performance) between all nodes to operate stably. While on
communication between nodes its highly recommended to have a multicast
setups with a small node count a network with higher latencies may work, this
capable network. The network should not be used heavily by other members,
is not guaranteed and gets rather unlikely with more than three nodes and
ideally corosync runs on its own network.
latencies above around 10 ms.
never share it with network where storage communicates too.
The network should not be used heavily by other members, as while corosync does
Before setting up a cluster it is good practice to check if the network is fit
not uses much bandwidth it is sensitive to latency jitters; ideally corosync
for that purpose.
runs on its own physically separated network. Especially do not use a shared
Ensure that all nodes are in the same subnet. This must only be true for the
network for corosync and storage (except as a potential low-priority fallback
  network interfaces used for cluster communication (corosync).
in a redundant configuration).
Ensure all nodes can reach each other over those interfaces, using ping is
Before setting up a cluster, it is good practice to check if the network is fit
  enough for a basic test.
for that purpose. To ensure that the nodes can connect to each other on the
Ensure that multicast works in general and a high package rates. This can be
cluster network, you can test the connectivity between them with the ping
  done with the omping tool. The final "%loss" number should be < 1%.
tool.
omping -c 10000 -i 0.001 -F -q NODE1-IP NODE2-IP ...
If the Proxmox VE firewall is enabled, ACCEPT rules for corosync will automatically
Ensure that multicast communication works over an extended period of time.
be generated - no manual action is required.
  This covers up problems where IGMP snooping is activated on the network but
Corosync used Multicast before version 3.0 (introduced in Proxmox VE 6.0).
  no multicast querier is active. This test has a duration of around 10
Modern versions rely on Kronosnet for cluster
  minutes.
communication, which, for now, only supports regular UDP unicast.
omping -c 600 -i 1 -q NODE1-IP NODE2-IP ...
You can still enable Multicast or legacy unicast by setting your
Your network is not ready for clustering if any of these test fails. Recheck
transport to udp or udpu in your corosync.conf,
your network configuration. Especially switches are notorious for having
but keep in mind that this will disable all cryptography and redundancy support.
multicast disabled by default or IGMP snooping enabled with no IGMP querier
This is therefore not recommended.
active.
In smaller cluster its also an option to use unicast if you really cannot get
multicast to work.
Separate Cluster Network
Separate Cluster Network
When creating a cluster without any parameters the cluster network is generally
When creating a cluster without any parameters, the corosync cluster network is
shared with the Web UI and the VMs and its traffic. Depending on your setup
generally shared with the web interface and the VMs' network. Depending on
even storage traffic may get sent over the same network. Its recommended to
your setup, even storage traffic may get sent over the same network. It&#8217;s
change that, as corosync is a time critical real time application.
recommended to change that, as corosync is a time-critical, real-time
Setting Up A New Network
application.
First you have to setup a new network interface. It should be on a physical
Setting Up a New Network
First, you have to set up a new network interface. It should be on a physically
separate network. Ensure that your network fulfills the
separate network. Ensure that your network fulfills the
cluster network requirements.
cluster network requirements.
Separate On Cluster Creation
Separate On Cluster Creation
This is possible through the ring0_addr and bindnet0_addr parameter of
This is possible via the linkX parameters of the pvecm create
the pvecm create command used for creating a new cluster.
command, used for creating a new cluster.
If you have setup a additional NIC with a static address on 10.10.10.1/25
If you have set up an additional NIC with a static address on 10.10.10.1/25,
and want to send and receive all cluster communication over this interface
and want to send and receive all cluster communication over this interface,
you would execute:
you would execute:
pvecm create test --ring0_addr 10.10.10.1 --bindnet0_addr 10.10.10.0
pvecm create test --link0 10.10.10.1
To check if everything is working properly execute:
To check if everything is working properly, execute:
systemctl status corosync
systemctl status corosync
Afterwards, proceed as described above to
add nodes with a separated cluster network.
Separate After Cluster Creation
Separate After Cluster Creation
You can do this also if you have already created a cluster and want to switch
You can do this if you have already created a cluster and want to switch
its communication to another network, without rebuilding the whole cluster.
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
This change may lead to short periods of quorum loss in the cluster, as nodes
have to restart corosync and come up one after the other on the new network.
have to restart corosync and come up one after the other on the new network.
Check how to edit the corosync.conf file first.
Check how to edit the corosync.conf file first.
The open it and you should see a file similar to:
Then, open it and you should see a file similar to:
logging {
logging {
   debug: off
   debug: off
Line 328: Line 386:
}
}
totem {
totem {
   cluster_name: thomas-testcluster
   cluster_name: testcluster
   config_version: 3
   config_version: 3
   ip_version: ipv4
   ip_version: ipv4-6
   secauth: on
   secauth: on
   version: 2
   version: 2
   interface {
   interface {
     bindnetaddr: 192.168.30.50
     linknumber: 0
    ringnumber: 0
   }
   }
}
}
The first you want to do is add the name properties in the node entries if
ringX_addr actually specifies a corosync link address. The name "ring"
you do not see them already. Those must match the node name.
is a remnant of older corosync versions that is kept for backwards
Then replace the address from the ring0_addr properties with the new
compatibility.
addresses. You may use plain IP addresses or also hostnames here. If you use
The first thing you want to do is add the name properties in the node entries,
hostnames ensure that they are resolvable from all nodes.
if you do not see them already. Those must match the node name.
In my example I want to switch my cluster communication to the 10.10.10.1/25
Then replace all addresses from the ring0_addr properties of all nodes with
network. So I replace all ring0_addr respectively. I also set the bindetaddr
the new addresses. You may use plain IP addresses or hostnames here. If you use
in the totem section of the config to an address of the new network. It can be
hostnames, ensure that they are resolvable from all nodes (see also
any address from the subnet configured on the new network interface.
Link Address Types).
After you increased the config_version property the new configuration file
In this example, we want to switch cluster communication to the
10.10.10.0/25 network, so we change the ring0_addr of each node respectively.
The exact same procedure can be used to change other ringX_addr values
as well. However, we recommend only changing one link address at a time, so
that it&#8217;s easier to recover if something goes wrong.
After we increase the config_version property, the new configuration file
should look like:
should look like:
logging {
logging {
Line 377: Line 439:
}
}
totem {
totem {
   cluster_name: thomas-testcluster
   cluster_name: testcluster
   config_version: 4
   config_version: 4
   ip_version: ipv4
   ip_version: ipv4-6
   secauth: on
   secauth: on
   version: 2
   version: 2
   interface {
   interface {
     bindnetaddr: 10.10.10.1
     linknumber: 0
    ringnumber: 0
   }
   }
}
}
Now after a final check whether all changed information is correct we save it
Then, after a final check to see that all changed information is correct, we
and see again the edit corosync.conf file section to
save it and once again follow the
learn how to bring it in effect.
edit corosync.conf file section to bring it into
As our change cannot be enforced live from corosync we have to do an restart.
effect.
The changes will be applied live, so restarting corosync is not strictly
necessary. If you changed other settings as well, or notice corosync
complaining, you can optionally trigger a restart.
On a single node execute:
On a single node execute:
systemctl restart corosync
systemctl restart corosync
Now check if everything is fine:
Now check if everything is okay:
systemctl status corosync
systemctl status corosync
If corosync runs again correct restart corosync also on all other nodes.
If corosync begins to work again, restart it on all other nodes too.
They will then join the cluster membership one by one on the new network.
They will then join the cluster membership one by one on the new network.
Redundant Ring Protocol
Corosync Addresses
To avoid a single point of failure you should implement counter measurements.
A corosync link address (for backwards compatibility denoted by ringX_addr in
This can be on the hardware and operating system level through network bonding.
corosync.conf) can be specified in two ways:
Corosync itself offers also a possibility to add redundancy through the so
IPv4/v6 addresses can be used directly. They are recommended, since they
called Redundant Ring Protocol. This protocol allows running a second totem
are static and usually not changed carelessly.
ring on another network, this network should be physically separated from the
Hostnames will be resolved using getaddrinfo, which means that by
other rings network to actually increase availability.
default, IPv6 addresses will be used first, if available (see also
RRP On Cluster Creation
man gai.conf). Keep this in mind, especially when upgrading an existing
The pvecm create command provides the additional parameters bindnetX_addr,
cluster to IPv6.
ringX_addr and rrp_mode, can be used for RRP configuration.
Hostnames should be used with care, since the addresses they
See the glossary if you do not know what each parameter means.
resolve to can be changed without touching corosync or the node it runs on -
So if you have two networks, one on the 10.10.10.1/24 and the other on the
which may lead to a situation where an address is changed without thinking
10.10.20.1/24 subnet you would execute:
about implications for corosync.
pvecm create CLUSTERNAME -bindnet0_addr 10.10.10.1 -ring0_addr 10.10.10.1 \
A separate, static hostname specifically for corosync is recommended, if
-bindnet1_addr 10.10.20.1 -ring1_addr 10.10.20.1
hostnames are preferred. Also, make sure that every node in the cluster can
RRP On A Created Cluster
resolve all hostnames correctly.
When enabling an already running cluster to use RRP you will take similar steps
Since Proxmox VE 5.1, while supported, hostnames will be resolved at the time of
as describe in
entry. Only the resolved IP is saved to the configuration.
separating the cluster network. You
Nodes that joined the cluster on earlier versions likely still use their
just do it on another ring.
unresolved hostname in corosync.conf. It might be a good idea to replace
First add a new interface subsection in the totem section, set its
them with IPs or a separate hostname, as mentioned above.
ringnumber property to 1. Set the interfaces bindnetaddr property to an
Corosync Redundancy
address of the subnet you have configured for your new ring.
Corosync supports redundant networking via its integrated Kronosnet layer by
Further set the rrp_mode to passive, this is the only stable mode.
default (it is not supported on the legacy udp/udpu transports). It can be
Then add to each node entry in the nodelist section its new ring1_addr
enabled by specifying more than one link address, either via the --linkX
property with the nodes additional ring address.
parameters of pvecm, in the GUI as Link 1 (while creating a cluster or
So if you have two networks, one on the 10.10.10.1/24 and the other on the
adding a new node) or by specifying more than one ringX_addr in
10.10.20.1/24 subnet, the final configuration file should look like:
corosync.conf.
totem {
To provide useful failover, every link should be on its own
   cluster_name: tweak
physical network connection.
   config_version: 9
Links are used according to a priority setting. You can configure this priority
  ip_version: ipv4
by setting knet_link_priority in the corresponding interface section in
   rrp_mode: passive
corosync.conf, or, preferably, using the priority parameter when creating
  secauth: on
your cluster with pvecm:
  version: 2
# pvecm create CLUSTERNAME --link0 10.10.10.1,priority=15 --link1 10.20.20.1,priority=20
  interface {
This would cause link1 to be used first, since it has the higher priority.
     bindnetaddr: 10.10.10.1
If no priorities are configured manually (or two links have the same priority),
     ringnumber: 0
links will be used in order of their number, with the lower number having higher
priority.
Even if all links are working, only the one with the highest priority will see
corosync traffic. Link priorities cannot be mixed, meaning that links with
different priorities will not be able to communicate with each other.
Since lower priority links will not see traffic unless all higher priorities
have failed, it becomes a useful strategy to specify networks used for
other tasks (VMs, storage, etc.) as low-priority links. If worst comes to
worst, a higher latency or more congested connection might be better than no
connection at all.
Adding Redundant Links To An Existing Cluster
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 the link number chosen above.
Assuming you added a link with number 1, the new configuration file could look
like this:
logging {
   debug: off
   to_syslog: yes
}
nodelist {
   node {
    name: due
    nodeid: 2
    quorum_votes: 1
     ring0_addr: 10.10.10.2
     ring1_addr: 10.20.20.2
   }
   }
   interface {
   node {
     bindnetaddr: 10.10.20.1
     name: tre
     ringnumber: 1
    nodeid: 3
    quorum_votes: 1
    ring0_addr: 10.10.10.3
     ring1_addr: 10.20.20.3
   }
   }
}
nodelist {
   node {
   node {
     name: pvecm1
     name: uno
     nodeid: 1
     nodeid: 1
     quorum_votes: 1
     quorum_votes: 1
     ring0_addr: 10.10.10.1
     ring0_addr: 10.10.10.1
     ring1_addr: 10.10.20.1
     ring1_addr: 10.20.20.1
  }
}
quorum {
  provider: corosync_votequorum
}
totem {
  cluster_name: testcluster
  config_version: 4
  ip_version: ipv4-6
  secauth: on
  version: 2
  interface {
    linknumber: 0
   }
   }
node {
  interface {
     name: pvecm2
     linknumber: 1
    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
The new link will be enabled as soon as you follow the last steps to
Bring it in effect like described in the
edit the corosync.conf file. A restart should not
edit the corosync.conf file section.
be necessary. You can check that corosync loaded the new link using:
This is a change which cannot take live in effect and needs at least a restart
journalctl -b -u corosync
of corosync. Recommended is a restart of the whole cluster.
It might be a good idea to test the new link by temporarily disconnecting the
If you cannot reboot the whole cluster ensure no High Availability services are
old link on one node and making sure that its status remains online while
configured and the stop the corosync service on all nodes. After corosync is
disconnected:
stopped on all nodes start it one after the other again.
pvecm status
If you see a healthy cluster state, it means that your new link is being used.
Role of SSH in Proxmox VE Clusters
Proxmox VE utilizes SSH tunnels for various features.
Proxying console/shell sessions (node and guests)
When using the shell for node B while being connected to node A, connects to a
terminal proxy on node A, which is in turn connected to the login shell on node
B via a non-interactive SSH tunnel.
VM and CT memory and local-storage migration in secure mode.
During the migration, one or more SSH tunnel(s) are established between the
source and target nodes, in order to exchange migration information and
transfer memory and disk contents.
Storage replication
Pitfalls due to automatic execution of .bashrc and siblings
In case you have a custom .bashrc, or similar files that get executed on
login by the configured shell, ssh will automatically run it once the session
is established successfully. This can cause some unexpected behavior, as those
commands may be executed with root permissions on any of the operations
described above. This can cause possible problematic side-effects!
In order to avoid such complications, it&#8217;s recommended to add a check in
/root/.bashrc to make sure the session is interactive, and only then run
.bashrc commands.
You can add this snippet at the beginning of your .bashrc file:
# Early exit if not running interactively to avoid side-effects!
case $- in
    *i*) ;;
      *) return;;
esac
Corosync External Vote Support
This section describes a way to deploy an external voter in a Proxmox VE cluster.
When configured, the cluster can sustain more node failures without
violating safety properties of the cluster communication.
For this to work, there are two services involved:
A QDevice daemon which runs on each Proxmox VE node
An external vote daemon which runs on an independent server
As a result, you can achieve higher availability, even in smaller setups (for
example 2+1 nodes).
QDevice Technical Overview
The Corosync Quorum Device (QDevice) is a daemon which runs on each cluster
node. It provides a configured number of votes to the cluster&#8217;s quorum
subsystem, based on an externally running third-party arbitrator&#8217;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) after
receiving the third-party vote.
Currently, only QDevice Net is supported as a third-party arbitrator. This is
a daemon which provides a vote to a cluster partition, if it can reach the
partition members over the network. It will only give votes to one partition
of a cluster at any time.
It&#8217;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 only requirements for the external host are that it needs network access to
the cluster and to have a corosync-qnetd package available. We provide a package
for Debian based hosts, and other Linux distributions should also have a package
available through their respective package manager.
Unlike corosync itself, a QDevice connects to the cluster over TCP/IP.
The daemon can also run outside the LAN of the cluster and isn&#8217;t limited to the
low latencies requirements of corosync.
Supported Setups
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 currently discourage the use of
QDevices. The reason for this is the difference in the votes which the QDevice
provides for each cluster type. Even numbered clusters get a single additional
vote, which only increases availability, because if the QDevice
itself fails, you are in the same position as with no QDevice at all.
On the other hand, with an odd numbered cluster size, the QDevice provides
(N-1) votes&#8201;&#8212;&#8201;where N corresponds to the cluster node count. This
alternative behavior makes sense; if it had only one additional vote, the
cluster could get into a split-brain situation. This algorithm allows for all
nodes but one (and naturally the QDevice itself) to fail. However, there are two
drawbacks to this:
If the QNet daemon itself fails, no other node may fail or the cluster
  immediately loses quorum. For example, in a cluster with 15 nodes, 7
  could fail before the cluster becomes inquorate. But, if a QDevice is
  configured here and it itself fails, no single node of the 15 may fail.
  The QDevice acts almost as a single point of failure in this case.
The fact that all but one node plus QDevice may fail sounds promising at
  first, but this may result in a mass recovery of HA services, which could
  overload the single remaining node. Furthermore, a Ceph server will stop
  providing services if only ((N-1)/2) nodes or less remain online.
If you understand the drawbacks and implications, you can decide yourself if
you want to use this technology in an odd numbered cluster setup.
QDevice-Net Setup
We recommend running 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 integration of the QDevice in Proxmox VE.
First, install the corosync-qnetd package on your external server
external# apt install corosync-qnetd
and the corosync-qdevice package on all cluster nodes
pve# apt install corosync-qdevice
After doing this, ensure that all the nodes in the cluster are online.
You can now set up your QDevice by running the following command on one
of the Proxmox VE nodes:
pve# pvecm qdevice setup &lt;QDEVICE-IP&gt;
The SSH key from the cluster will be automatically copied to the QDevice.
Make sure to setup key-based access for the root user on your external
server, or temporarily allow root login with password during the setup phase.
If you receive an error such as Host key verification failed. at this
stage, running pvecm updatecerts could fix the issue.
After all the steps have successfully completed, you will see "Done". You can
verify that the QDevice has been set up with:
pve# pvecm status
...
Votequorum information
~~~~~~~~~~~~~~~~~~~~~
Expected votes:  3
Highest expected: 3
Total votes:      3
Quorum:          2
Flags:            Quorate Qdevice
Membership information
~~~~~~~~~~~~~~~~~~~~~~
    Nodeid      Votes    Qdevice Name
    0x00000001      1    A,V,NMW 192.168.22.180 (local)
    0x00000002      1    A,V,NMW 192.168.22.181
    0x00000000      1            Qdevice
QDevice Status Flags
The status output of the QDevice, as seen above, will usually contain three
columns:
A / NA: Alive or Not Alive. Indicates if the communication to the external
    corosync-qnetd daemon works.
V / NV: If the QDevice will cast a vote for the node. In a split-brain
    situation, where the corosync connection between the nodes is down, but they
    both can still communicate with the external corosync-qnetd daemon,
    only one node will get the vote.
MW / NMW: Master wins (MV) or not (NMW). Default is NMW, see
  [votequorum_qdevice_master_wins manual page
  https://manpages.debian.org/bookworm/libvotequorum-dev/votequorum_qdevice_master_wins.3.en.html].
NR: QDevice is not registered.
If your QDevice is listed as Not Alive (NA in the output above),
ensure that port 5403 (the default port of the qnetd server) of your external
server is reachable via TCP/IP!
Frequently Asked Questions
Tie Breaking
In case of a tie, where two same-sized cluster partitions cannot see each other
but can see the QDevice, the QDevice chooses one of those partitions randomly
and provides a vote to it.
Possible Negative Implications
For clusters with an even node count, there are no negative implications when
using a QDevice. If it fails to work, it is the same as not having a QDevice
at all.
Adding/Deleting Nodes After QDevice Setup
If you want to add a new node or remove an existing one from a cluster with a
QDevice setup, you need to remove the QDevice first. After that, you can add or
remove nodes normally. Once you have a cluster with an even node count again,
you can set up the QDevice again as described previously.
Removing the QDevice
If you used the official pvecm tool to add the QDevice, you can remove it
by running:
pve# pvecm qdevice remove
Corosync Configuration
Corosync Configuration
The /ect/pve/corosync.conf file plays a central role in Proxmox VE cluster. It
The /etc/pve/corosync.conf file plays a central role in a Proxmox VE cluster. It
controls the cluster member ship and its network.
controls the cluster membership and its network.
For reading more about it check the corosync.conf man page:
For further information about it, check the corosync.conf man page:
man corosync.conf
man corosync.conf
For node membership you should always use the pvecm tool provided by Proxmox VE.
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.
You may have to edit the configuration file manually for other changes.
Here are a few best practice tips for doing this.
Here are a few best practice tips for doing this.
Edit corosync.conf
Edit corosync.conf
Editing the corosync.conf file can be not always straight forward. There are
Editing the corosync.conf file is not always very straightforward. There are
two on each cluster, one in /etc/pve/corosync.conf and the other in
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
/etc/corosync/corosync.conf. Editing the one in our cluster file system will
propagate the changes to the local one, but not vice versa.
propagate the changes to the local one, but not vice versa.
The configuration will get updated automatically as soon as the file changes.
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
This means that 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
effect immediately. Thus, you should always make a copy and edit that instead,
avoid triggering some unwanted changes by an in between safe.
to avoid triggering unintended changes when saving the file while editing.
cp /etc/pve/corosync.conf /etc/pve/corosync.conf.new
cp /etc/pve/corosync.conf /etc/pve/corosync.conf.new
Then open the Config file with your favorite editor, nano and vim.tiny are
Then, open the config file with your favorite editor, such as nano or
preinstalled on Proxmox VE for example.
vim.tiny, which come pre-installed on every Proxmox VE node.
Always increment the config_version number on configuration changes,
Always increment the config_version number after configuration changes;
omitting this can lead to problems.
omitting this can lead to problems.
After making the necessary changes create another copy of the current working
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
configuration file. This serves as a backup if the new configuration fails to
apply or makes problems in other ways.
apply or causes other issues.
cp /etc/pve/corosync.conf /etc/pve/corosync.conf.bak
cp /etc/pve/corosync.conf /etc/pve/corosync.conf.bak
Then move the new configuration file over the old one:
Then replace the old configuration file with the new one:
mv /etc/pve/corosync.conf.new /etc/pve/corosync.conf
mv /etc/pve/corosync.conf.new /etc/pve/corosync.conf
You may check with the commands
You can check if the changes could be applied automatically, using the following
commands:
systemctl status corosync
systemctl status corosync
journalctl -b -u corosync
journalctl -b -u corosync
If the change could applied automatically. If not you may have to restart the
If the changes could not be applied automatically, you may have to restart the
corosync service via:
corosync service via:
systemctl restart corosync
systemctl restart corosync
On errors check the troubleshooting section below.
On errors, check the troubleshooting section below.
Troubleshooting
Troubleshooting
Issue: quorum.expected_votes must be configured
Issue: quorum.expected_votes must be configured
Line 509: Line 767:
     'configuration error: nodelist or quorum.expected_votes must be configured!'
     'configuration error: nodelist or quorum.expected_votes must be configured!'
[...]
[...]
It means that the hostname you set for corosync ringX_addr in the
It means that the hostname you set for a corosync ringX_addr in the
configuration could not be resolved.
configuration could not be resolved.
Write Configuration When Not Quorate
Write Configuration When Not Quorate
If you need to change /etc/pve/corosync.conf on an node with no quorum, and you
If you need to change /etc/pve/corosync.conf on a node with no quorum, and you
know what you do, use:
understand what you are doing, use:
pvecm expected 1
pvecm expected 1
This sets the expected vote count to 1 and makes the cluster quorate. You can
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.
then 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
This is not enough if corosync cannot start anymore. In that case, it is best to
local copy of the corosync configuration in /etc/corosync/corosync.conf so
edit the local copy of the corosync configuration in
that corosync can start again. Ensure that on all nodes this configuration has
/etc/corosync/corosync.conf, so that corosync can start again. Ensure that on
the same content to avoid split brains. If you are not sure what went wrong
all nodes, this configuration has the same content to avoid split-brain
it’s best to ask the Proxmox Community to help you.
situations.
Corosync Configuration Glossary
Corosync Configuration Glossary
ringX_addr
ringX_addr
This names the different ring addresses for the corosync totem rings used for
This names the different link addresses for the Kronosnet connections between
the cluster communication.
nodes.
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
Cluster Cold Start
It is obvious that a cluster is not quorate when all nodes are
It is obvious that a cluster is not quorate when all nodes are
offline. This is a common case after a power failure.
offline. This is a common case after a power failure.
It is always a good idea to use an uninterruptible power supply
It is always a good idea to use an uninterruptible power supply
(“UPS”, also called “battery backup”) to avoid this state, especially if
(&#8220;UPS&#8221;, also called &#8220;battery backup&#8221;) to avoid this state, especially if
you want HA.
you want HA.
On node startup, service pve-manager is started and waits for
On node startup, the pve-guests service is started and waits for
quorum. Once quorate, it starts all guests which have the onboot
quorum. Once quorate, it starts all guests which have the onboot
flag set.
flag set.
When you turn on nodes, or when power comes back after power failure,
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
it is likely that some nodes will boot faster than others. Please keep in
mind that guest startup is delayed until you reach quorum.
mind that guest startup is delayed until you reach quorum.
Guest VMID Auto-Selection
When creating new guests the web interface will ask the backend for a free VMID
automatically. The default range for searching is 100 to 1000000 (lower
than the maximal allowed VMID enforced by the schema).
Sometimes admins either want to allocate new VMIDs in a separate range, for
example to easily separate temporary VMs with ones that choose a VMID manually.
Other times its just desired to provided a stable length VMID, for which
setting the lower boundary to, for example, 100000 gives much more room for.
To accommodate this use case one can set either lower, upper or both boundaries
via the datacenter.cfg configuration file, which can be edited in the web
interface under Datacenter &#8594; Options.
The range is only used for the next-id API call, so it isn&#8217;t a hard
limit.
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.
It makes a difference if a guest is online or offline, or if it has
local resources (like a local disk).
For details about virtual machine migration, see the
QEMU/KVM Migration Chapter.
For details about container migration, see the
Container Migration Chapter.
Migration Type
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 is 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.
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 insecure 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 both 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 all migration traffic. In addition to the memory,
this also affects the storage traffic for offline migrations.
The migration network is set as a network using CIDR notation. This
has the advantage that you don&#8217;t 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 exactly 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 eno1 inet manual
# public network
auto vmbr0
iface vmbr0 inet static
    address 192.X.Y.57/24
    gateway 192.X.Y.1
    bridge-ports eno1
    bridge-stp off
    bridge-fd 0
# cluster network
auto eno2
iface eno2 inet static
    address  10.1.1.1/24
# fast network
auto eno3
iface eno3 inet static
    address  10.1.2.1/24
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
The migration type must always be set when the migration network
is set in /etc/pve/datacenter.cfg.
</pvehide>
</pvehide>
<!--PVE_IMPORT_END_MARKER-->
<!--PVE_IMPORT_END_MARKER-->
[[Category:Proxmox VE 4.x]]

Latest revision as of 17:30, 6 March 2024

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. There’s no explicit limit for the number of nodes in a cluster. In practice, the actual possible node count may be limited by the host and network performance. Currently (2021), there are reports of clusters (using high-end enterprise hardware) with over 50 nodes in production.

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 tasks

  • Use of pmxcfs, a 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 able to connect to each other via UDP ports 5405-5412 for corosync to work.

  • Date and time must be synchronized.

  • An SSH tunnel on TCP port 22 between nodes is required.

  • 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.

  • The root password of a cluster node is required for adding nodes.

  • Online migration of virtual machines is only supported when nodes have CPUs from the same vendor. It might work otherwise, but this is never guaranteed.

Note It is not possible to mix Proxmox VE 3.x and earlier with Proxmox VE 4.X cluster nodes.
Note While it’s possible to mix Proxmox VE 4.4 and Proxmox VE 5.0 nodes, doing so is not supported as a production configuration and should only be done temporarily, during an upgrade of the whole cluster from one major version to another.
Note Running a cluster of Proxmox VE 6.x with earlier versions is not possible. The cluster protocol (corosync) between Proxmox VE 6.x and earlier versions changed fundamentally. The corosync 3 packages for Proxmox VE 5.4 are only intended for the upgrade procedure to Proxmox VE 6.0.

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.

While it’s common to reference all node names and their IPs in /etc/hosts (or make their names resolvable through other means), this is not necessary for a cluster to work. It may be useful however, as you can then connect from one node to another via SSH, using the easier to remember node name (see also Link Address Types). Note that we always recommend referencing nodes by their IP addresses in the cluster configuration.

Create a Cluster

You can either create a cluster on the console (login via ssh), or through the API using the Proxmox VE web interface (Datacenter → Cluster).

Note Use a unique name for your cluster. This name cannot be changed later. The cluster name follows the same rules as node names.

Create via Web GUI

screenshot/gui-cluster-create.png

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

As of Proxmox VE 6.2, up to 8 fallback links can be added to a cluster. To add a redundant link, click the Add button and select a link number and IP address from the respective fields. Prior to Proxmox VE 6.2, 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).

Note Ensure that the network selected for cluster communication is not used for any high traffic purposes, like network storage or live-migration. While the cluster network itself produces small amounts of data, it is very sensitive to latency. Check out full cluster network requirements.

Create via the Command Line

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

 hp1# pvecm create CLUSTERNAME

To check the state of the new cluster use:

 hp1# pvecm status

Multiple Clusters in the Same Network

It is possible to create multiple clusters in the same physical or logical network. In this case, each cluster must have a unique name to avoid possible clashes in the cluster communication stack. Furthermore, this 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.

Adding Nodes to the Cluster

Caution All existing configuration in /etc/pve is overwritten when joining a cluster. In particular, a joining node cannot hold any guests, since guest IDs could otherwise conflict, and the node will inherit the cluster’s storage configuration. To join a node with existing guest, as a workaround, you can create a backup of each guest (using vzdump) and restore it under a different ID after joining. If the node’s storage layout differs, you will need to re-add the node’s storages, and adapt each storage’s node restriction to reflect on which nodes the storage is actually available.

Join Node to Cluster via GUI

screenshot/gui-cluster-join-information.png

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

screenshot/gui-cluster-join.png

Next, log in 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.

Note To enter all required data manually, you can disable the Assisted Join checkbox.

After clicking the Join button, the cluster join process will start immediately. After the node has joined the cluster, its current node certificate will be replaced by one signed from the cluster certificate authority (CA). This means that the current session will stop working after a few seconds. You then might need to force-reload the web interface and log in again with the cluster credentials.

Now your node should be visible under Datacenter → Cluster.

Join Node to Cluster via Command Line

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

 # pvecm add IP-ADDRESS-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:

 # pvecm status
Cluster status after adding 4 nodes
 # pvecm status
Cluster information
~~~~~~~~~~~~~~~~~~~
Name:             prod-central
Config Version:   3
Transport:        knet
Secure auth:      on

Quorum information
~~~~~~~~~~~~~~~~~~
Date:             Tue Sep 14 11:06:47 2021
Quorum provider:  corosync_votequorum
Nodes:            4
Node ID:          0x00000001
Ring ID:          1.1a8
Quorate:          Yes

Votequorum information
~~~~~~~~~~~~~~~~~~~~~~
Expected votes:   4
Highest expected: 4
Total votes:      4
Quorum:           3
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 a list of all nodes, use:

 # pvecm nodes
List nodes in a cluster
 # 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 link0 parameter to set the nodes address on that network:

# pvecm add IP-ADDRESS-CLUSTER --link0 LOCAL-IP-ADDRESS-LINK0

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 X fields in the Cluster Join dialog.

Remove a Cluster Node

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

Move all virtual machines from the node. Ensure that you have made copies of any local data or backups that you want to keep. In addition, make sure to remove any scheduled replication jobs to the node to be removed.

Caution Failure to remove replication jobs to a node before removing said node will result in the replication job becoming irremovable. Especially note that replication automatically switches direction if a replicated VM is migrated, so by migrating a replicated VM from a node to be deleted, replication jobs will be set up to that node automatically.

In the following example, we will remove the node hp4 from the cluster.

Log in to a different cluster node (not hp4), and issue a pvecm nodes command to identify the node ID to remove:

 hp1# pvecm nodes

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

At this point, you must power off hp4 and ensure that it will not power on again (in the network) with its current configuration.

Important As mentioned above, it is critical to power off the node before removal, and make sure that it will not power on again (in the existing cluster network) with its current configuration. If you power on the node as it is, the cluster could end up broken, and it could be difficult to restore it to a functioning state.

After powering off the node hp4, we can safely remove it from the cluster.

 hp1# pvecm delnode hp4
 Killing node 4
Note At this point, it is possible that you will receive an error message stating Could not kill node (error = CS_ERR_NOT_EXIST). This does not signify an actual failure in the deletion of the node, but rather a failure in corosync trying to kill an offline node. Thus, it can be safely ignored.

Use pvecm nodes or pvecm status to check the node list again. It should look something like:

hp1# pvecm status

...

Votequorum information
~~~~~~~~~~~~~~~~~~~~~~
Expected votes:   3
Highest expected: 3
Total votes:      3
Quorum:           2
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

If, for whatever reason, you want this server to join the same cluster again, you have to:

  • do a fresh install of Proxmox VE on it,

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

The configuration files for the removed node will still reside in /etc/pve/nodes/hp4. Recover any configuration you still need and remove the directory afterwards.

Note After removal of the node, its SSH fingerprint will still reside in the known_hosts of the other nodes. If you receive an SSH error after rejoining a node with the same IP or hostname, run pvecm updatecerts once on the re-added node to update its fingerprint cluster wide.

Separate a Node Without Reinstalling

Caution This is not the recommended method, proceed with caution. Use the previous 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 any shared storage. 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. Furthermore, it may also lead to VMID conflicts.

It’s 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. It’s just important that the exact same storage does not get accessed by multiple clusters. After setting up this storage, move all data and VMs from the node to it. Then you are ready to separate the node from the cluster.

Warning Ensure that all shared resources are cleanly separated! Otherwise you will run into conflicts and problems.

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

systemctl stop pve-cluster
systemctl stop corosync

Start the cluster file system again in local mode:

pmxcfs -l

Delete the corosync configuration files:

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

You can now start the file system again as a normal service:

killall pmxcfs
systemctl start pve-cluster

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

pvecm delnode oldnode

If the command fails due to a loss of quorum in the remaining node, you can set the expected votes to 1 as a workaround:

pvecm expected 1

And then repeat the pvecm delnode command.

Now switch back to the separated node and delete all the remaining cluster files on it. 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 file system, you may want to clean those up too. After making absolutely sure that you have the correct node name, you can simply remove the entire directory recursively from /etc/pve/nodes/NODENAME.

Caution The node’s SSH keys will remain in the authorized_key file. This means that the nodes can still connect to each other with public key authentication. You should fix this 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 reliably 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

The Proxmox VE cluster stack requires a reliable network with latencies under 5 milliseconds (LAN performance) between all nodes to operate stably. While on setups with a small node count a network with higher latencies may work, this is not guaranteed and gets rather unlikely with more than three nodes and latencies above around 10 ms.

The network should not be used heavily by other members, as while corosync does not uses much bandwidth it is sensitive to latency jitters; ideally corosync runs on its own physically separated network. Especially 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 ensure that 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.

Note Corosync used Multicast before version 3.0 (introduced in Proxmox VE 6.0). Modern versions rely on Kronosnet for cluster communication, which, for now, only supports regular UDP unicast.
Caution You can still enable Multicast or legacy unicast by setting your transport to udp or udpu in your corosync.conf, but keep in mind that this will disable all cryptography and redundancy support. This is therefore not recommended.

Separate Cluster Network

When creating a cluster without any parameters, the corosync cluster network is generally shared with the web interface and the VMs' network. Depending on your setup, even storage traffic may get sent over the same network. It’s recommended to change that, as corosync is a time-critical, real-time application.

Setting Up a New Network

First, you have to set up a new network interface. It should be on a physically separate network. Ensure that your network fulfills the cluster network requirements.

Separate On Cluster Creation

This is possible via the linkX parameters of the pvecm create command, used for creating a new cluster.

If you have set up an 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 --link0 10.10.10.1

To check if everything is working properly, execute:

systemctl status corosync

Afterwards, proceed as described above to add nodes with a separated cluster network.

Separate After Cluster Creation

You can do this 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 periods 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. Then, 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: testcluster
  config_version: 3
  ip_version: ipv4-6
  secauth: on
  version: 2
  interface {
    linknumber: 0
  }

}
Note ringX_addr actually specifies a corosync link address. The name "ring" is a remnant of older corosync versions that is kept for backwards compatibility.

The first thing 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 all addresses from the ring0_addr properties of all nodes with the new addresses. You may use plain IP addresses or hostnames here. If you use hostnames, ensure that they are resolvable from all nodes (see also Link Address Types).

In this example, we want to switch cluster communication to the 10.10.10.0/25 network, so we change the ring0_addr of each node respectively.

Note The exact same procedure can be used to change other ringX_addr values as well. However, we recommend only changing one link address at a time, so that it’s easier to recover if something goes wrong.

After we increase 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: testcluster
  config_version: 4
  ip_version: ipv4-6
  secauth: on
  version: 2
  interface {
    linknumber: 0
  }

}

Then, after a final check to see that all changed information is correct, we save it and once again follow the edit corosync.conf file section to bring it into effect.

The changes will be applied live, so restarting corosync is not strictly necessary. If you changed other settings as well, or notice corosync complaining, you can optionally trigger a restart.

On a single node execute:

systemctl restart corosync

Now check if everything is okay:

systemctl status corosync

If corosync begins to work again, restart it on all other nodes too. They will then join the cluster membership one by one on the new network.

Corosync Addresses

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

  • IPv4/v6 addresses can be used directly. They are recommended, since they are static and usually not changed carelessly.

  • Hostnames will be resolved using getaddrinfo, which means that by default, IPv6 addresses will be used first, if available (see also man gai.conf). Keep this in mind, especially when upgrading an existing cluster to IPv6.

Caution Hostnames should be used with care, since the addresses they resolve to can be changed without touching corosync or the node it runs on - which may lead to a situation where an address is changed without thinking about implications for corosync.

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 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.

Corosync Redundancy

Corosync supports redundant networking via its integrated Kronosnet layer by default (it is not supported on the legacy udp/udpu transports). It can be enabled by specifying more than one link address, either via the --linkX parameters of pvecm, in the GUI as Link 1 (while creating a cluster or adding a new node) or by specifying more than one ringX_addr in corosync.conf.

Note To provide useful failover, every link should be on its own physical network connection.

Links are used according to a priority setting. You can configure this priority by setting knet_link_priority in the corresponding interface section in corosync.conf, or, preferably, using the priority parameter when creating your cluster with pvecm:

 # pvecm create CLUSTERNAME --link0 10.10.10.1,priority=15 --link1 10.20.20.1,priority=20

This would cause link1 to be used first, since it has the higher priority.

If no priorities are configured manually (or two links have the same priority), links will be used in order of their number, with the lower number having higher priority.

Even if all links are working, only the one with the highest priority will see corosync traffic. Link priorities cannot be mixed, meaning that links with different priorities will not be able to communicate with each other.

Since lower priority links will not see traffic unless all higher priorities have failed, it becomes a useful strategy to specify networks used for other tasks (VMs, storage, etc.) as low-priority links. If worst comes to worst, a higher latency or more congested connection might be better than no connection at all.

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 the link number chosen above.

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

logging {
  debug: off
  to_syslog: yes
}

nodelist {

  node {
    name: due
    nodeid: 2
    quorum_votes: 1
    ring0_addr: 10.10.10.2
    ring1_addr: 10.20.20.2
  }

  node {
    name: tre
    nodeid: 3
    quorum_votes: 1
    ring0_addr: 10.10.10.3
    ring1_addr: 10.20.20.3
  }

  node {
    name: uno
    nodeid: 1
    quorum_votes: 1
    ring0_addr: 10.10.10.1
    ring1_addr: 10.20.20.1
  }

}

quorum {
  provider: corosync_votequorum
}

totem {
  cluster_name: testcluster
  config_version: 4
  ip_version: ipv4-6
  secauth: on
  version: 2
  interface {
    linknumber: 0
  }
  interface {
    linknumber: 1
  }
}

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:

journalctl -b -u corosync

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:

pvecm status

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

Role of SSH in Proxmox VE Clusters

Proxmox VE utilizes SSH tunnels for various features.

  • Proxying console/shell sessions (node and guests)

    When using the shell for node B while being connected to node A, connects to a terminal proxy on node A, which is in turn connected to the login shell on node B via a non-interactive SSH tunnel.

  • VM and CT memory and local-storage migration in secure mode.

    During the migration, one or more SSH tunnel(s) are established between the source and target nodes, in order to exchange migration information and transfer memory and disk contents.

  • Storage replication

SSH setup

On Proxmox VE systems, the following changes are made to the SSH configuration/setup:

  • the root user’s SSH client config gets setup to prefer AES over ChaCha20

  • the root user’s authorized_keys file gets linked to /etc/pve/priv/authorized_keys, merging all authorized keys within a cluster

  • sshd is configured to allow logging in as root with a password

Note Older systems might also have /etc/ssh/ssh_known_hosts set up as symlink pointing to /etc/pve/priv/known_hosts, containing a merged version of all node host keys. This system was replaced with explicit host key pinning in pve-cluster <<INSERT VERSION>>, the symlink can be deconfigured if still in place by running pvecm updatecerts --unmerge-known-hosts.

Pitfalls due to automatic execution of .bashrc and siblings

In case you have a custom .bashrc, or similar files that get executed on login by the configured shell, ssh will automatically run it once the session is established successfully. This can cause some unexpected behavior, as those commands may be executed with root permissions on any of the operations described above. This can cause possible problematic side-effects!

In order to avoid such complications, it’s recommended to add a check in /root/.bashrc to make sure the session is interactive, and only then run .bashrc commands.

You can add this snippet at the beginning of your .bashrc file:

# Early exit if not running interactively to avoid side-effects!
case $- in
    *i*) ;;
      *) return;;
esac

Corosync External Vote Support

This section describes a way to deploy an external voter in a Proxmox VE cluster. When configured, the cluster can sustain more node failures without violating safety properties of the cluster communication.

For this to work, there are two services involved:

  • A QDevice daemon which runs on each Proxmox VE node

  • An external vote daemon which runs on an independent server

As a result, you can achieve higher availability, even in smaller setups (for example 2+1 nodes).

QDevice Technical Overview

The Corosync Quorum Device (QDevice) is a daemon which runs on each cluster node. It provides a configured number of votes to the cluster’s quorum subsystem, based on an externally 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) after receiving the third-party vote.

Currently, only QDevice Net is supported as a third-party arbitrator. This is a daemon which provides a vote to a cluster partition, if it can reach the partition members over the network. It will only give 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 only requirements for the external host are that it needs network access to the cluster and to have a corosync-qnetd package available. We provide a package for Debian based hosts, and other Linux distributions should also have a package available through their respective package manager.

Note Unlike corosync itself, a QDevice connects to the cluster over TCP/IP. The daemon can also run outside the LAN of the cluster and isn’t limited to the low latencies requirements of corosync.

Supported Setups

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 currently discourage the use of QDevices. The reason for this is the difference in the votes which the QDevice provides for each cluster type. Even numbered clusters get a single additional vote, which only increases availability, because if the QDevice itself fails, you are in the same position as with no QDevice at all.

On the other hand, with an odd numbered cluster size, the QDevice provides (N-1) votes — where N corresponds to the cluster node count. This alternative behavior makes sense; if it had only one additional vote, the cluster could get into a split-brain situation. This algorithm allows for all nodes but one (and naturally the QDevice itself) to fail. However, there are two drawbacks to this:

  • If the QNet daemon itself fails, no other node may fail or the cluster immediately loses quorum. For example, in a cluster with 15 nodes, 7 could fail before the cluster becomes inquorate. But, if a QDevice is configured here and it itself fails, no single node of the 15 may fail. The QDevice acts almost as a single point of failure in this case.

  • The fact that all but one node plus QDevice may fail sounds promising at first, but this may result in a mass recovery of HA services, which could overload the single remaining node. Furthermore, a Ceph server will stop providing services if only ((N-1)/2) nodes or less remain online.

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

QDevice-Net Setup

We recommend running 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 integration of the QDevice in Proxmox VE.

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

external# apt install corosync-qnetd

and the corosync-qdevice package on all cluster nodes

pve# apt install corosync-qdevice

After doing this, ensure that all the nodes in the cluster are online.

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

pve# pvecm qdevice setup <QDEVICE-IP>

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

Note Make sure to setup key-based access for the root user on your external server, or temporarily allow root login with password during the setup phase. If you receive an error such as Host key verification failed. at this stage, running pvecm updatecerts could fix the issue.

After all the steps have successfully completed, you will see "Done". You can verify that the QDevice has been set up with:

pve# pvecm status

...

Votequorum information
~~~~~~~~~~~~~~~~~~~~~
Expected votes:   3
Highest expected: 3
Total votes:      3
Quorum:           2
Flags:            Quorate Qdevice

Membership information
~~~~~~~~~~~~~~~~~~~~~~
    Nodeid      Votes    Qdevice Name
    0x00000001      1    A,V,NMW 192.168.22.180 (local)
    0x00000002      1    A,V,NMW 192.168.22.181
    0x00000000      1            Qdevice

QDevice Status Flags

The status output of the QDevice, as seen above, will usually contain three columns:

  • A / NA: Alive or Not Alive. Indicates if the communication to the external corosync-qnetd daemon works.

  • V / NV: If the QDevice will cast a vote for the node. In a split-brain situation, where the corosync connection between the nodes is down, but they both can still communicate with the external corosync-qnetd daemon, only one node will get the vote.

  • MW / NMW: Master wins (MV) or not (NMW). Default is NMW, see
    [votequorum_qdevice_master_wins manual page https://manpages.debian.org/bookworm/libvotequorum-dev/votequorum_qdevice_master_wins.3.en.html]
    .

  • NR: QDevice is not registered.

Note If your QDevice is listed as Not Alive (NA in the output above), ensure that port 5403 (the default port of the qnetd server) of your external server is reachable via TCP/IP!

Frequently Asked Questions

Tie Breaking

In case of a tie, where two same-sized cluster partitions cannot see each other but can see the QDevice, the QDevice chooses one of those partitions randomly and provides a vote to it.

Possible Negative Implications

For clusters with an even node count, there are no negative implications when using a QDevice. If it fails to work, it is the same as not having a QDevice at all.

Adding/Deleting Nodes After QDevice Setup

If you want to add a new node or remove an existing one from a cluster with a QDevice setup, you need to remove the QDevice first. After that, you can add or remove nodes normally. Once you have a cluster with an even node count again, you can set up the QDevice again as described previously.

Removing the QDevice

If you used the official pvecm tool to add the QDevice, you can remove it by running:

pve# pvecm qdevice remove

Corosync Configuration

The /etc/pve/corosync.conf file plays a central role in a Proxmox VE cluster. It controls the cluster membership and its network. For further information 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 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 that changes which can be integrated in a running corosync will take effect immediately. Thus, you should always make a copy and edit that instead, to avoid triggering unintended changes when saving the file while editing.

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

Then, open the config file with your favorite editor, such as nano or vim.tiny, which come pre-installed on every Proxmox VE node.

Note Always increment the config_version number after 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 causes other issues.

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

Then replace the old configuration file with the new one:

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

You can check if the changes could be applied automatically, using the following commands:

systemctl status corosync
journalctl -b -u corosync

If the changes could not be applied automatically, 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 a 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 a node with no quorum, and you understand what you are doing, use:

pvecm expected 1

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

This is not enough if corosync cannot start anymore. In that case, it is 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-brain situations.

Corosync Configuration Glossary

ringX_addr

This names the different link addresses for the Kronosnet connections between nodes.

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, the pve-guests service 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 will boot faster than others. Please keep in mind that guest startup is delayed until you reach quorum.

Guest VMID Auto-Selection

When creating new guests the web interface will ask the backend for a free VMID automatically. The default range for searching is 100 to 1000000 (lower than the maximal allowed VMID enforced by the schema).

Sometimes admins either want to allocate new VMIDs in a separate range, for example to easily separate temporary VMs with ones that choose a VMID manually. Other times its just desired to provided a stable length VMID, for which setting the lower boundary to, for example, 100000 gives much more room for.

To accommodate this use case one can set either lower, upper or both boundaries via the datacenter.cfg configuration file, which can be edited in the web interface under DatacenterOptions.

Note The range is only used for the next-id API call, so it isn’t a hard limit.

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.

It makes a difference if a guest is online or offline, or if it has local resources (like a local disk).

For details about virtual machine migration, see the QEMU/KVM Migration Chapter.

For details about container migration, see the Container Migration Chapter.

Migration Type

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 is 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.

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 insecure 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 both 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 all migration traffic. In addition to the memory, this also affects the storage traffic for offline migrations.

The migration network is set as a network using CIDR notation. This has the advantage that you don’t 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 exactly 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 eno1 inet manual

# public network
auto vmbr0
iface vmbr0 inet static
    address 192.X.Y.57/24
    gateway 192.X.Y.1
    bridge-ports eno1
    bridge-stp off
    bridge-fd 0

# cluster network
auto eno2
iface eno2 inet static
    address  10.1.1.1/24

# fast network
auto eno3
iface eno3 inet static
    address  10.1.2.1/24

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 is set in /etc/pve/datacenter.cfg.