Difference between revisions of "Cluster Manager"

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high-end enterprise hardware) with over 50 nodes in production.
 
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-related
+
leave the cluster, get status information, and do various other cluster-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 tasks
 
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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All nodes must be able to connect to each other via UDP ports 5404 and 5405
 
All nodes must be able to connect to each other via UDP ports 5404 and 5405
 
  for corosync to work.
 
  for corosync to work.
Date and time have to be synchronized.
+
Date and time must be synchronized.
SSH tunnel on TCP port 22 between nodes is used.
+
An SSH tunnel on TCP port 22 between nodes is required.
 
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.
Root password of a cluster node is required for adding nodes.
+
The root password of a cluster node is required for adding nodes.
 
It is not possible to mix Proxmox VE 3.x and earlier with Proxmox VE 4.X cluster
 
It is not possible to mix Proxmox VE 3.x and earlier with Proxmox VE 4.X cluster
 
nodes.
 
nodes.
While it’s possible to mix Proxmox VE 4.4 and Proxmox VE 5.0 nodes, doing so is
+
While it’s possible to mix Proxmox VE 4.4 and Proxmox VE 5.0 nodes, doing so is
not supported as production configuration and should only used temporarily
+
not supported as a production configuration and should only be done temporarily,
during upgrading the whole cluster from one to another major version.
+
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
 
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
 
cluster protocol (corosync) between Proxmox VE 6.x and earlier versions changed
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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.
While it’s common to reference all nodenames and their IPs in /etc/hosts (or
+
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
 
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
 
cluster to work. It may be useful however, as you can then connect from one node
to the other with SSH via the easier to remember node name (see also
+
to another via SSH, using the easier to remember node name (see also
 
Link Address Types). Note that we always
 
Link Address Types). Note that we always
recommend to reference nodes by their IP addresses in the cluster configuration.
+
recommend referencing nodes by their IP addresses in the cluster configuration.
 
Create a Cluster
 
Create a Cluster
 
You can either create a cluster on the console (login via ssh), or through
 
You can either create a cluster on the console (login via ssh), or through
the API using the Proxmox VE Webinterface (Datacenter → Cluster).
+
the API using the Proxmox VE web interface (Datacenter → Cluster).
 
Use a unique name for your cluster. This name cannot be changed later.
 
Use a unique name for your cluster. This name cannot be changed later.
 
The cluster name follows the same rules as node names.
 
The cluster name follows the same rules as node names.
 
Create via Web GUI
 
Create via Web GUI
 
Under Datacenter → Cluster, click on Create Cluster. Enter the cluster
 
Under Datacenter → Cluster, click on Create Cluster. Enter the cluster
name and select a network connection from the dropdown to serve as the main
+
name and select a network connection from the drop-down list to serve as the
cluster network (Link 0). It defaults to the IP resolved via the node’s
+
main cluster network (Link 0). It defaults to the IP resolved via the node’s
 
hostname.
 
hostname.
To add a second link as fallback, you can select the Advanced checkbox and
+
As of Proxmox VE 6.2, up to 8 fallback links can be added to a cluster. To add a
choose an additional network interface (Link 1, see also
+
redundant link, click the Add button and select a link number and IP address
Corosync Redundancy).
+
from the respective fields. Prior to Proxmox VE 6.2, to add a second link as
Ensure the network selected for the cluster communication is not used for
+
fallback, you can select the Advanced checkbox and choose an additional
any high traffic loads like those of (network) storages or live-migration.
+
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
 
While the cluster network itself produces small amounts of data, it is very
 
sensitive to latency. Check out full
 
sensitive to latency. Check out full
 
cluster network requirements.
 
cluster network requirements.
Create via Command Line
+
Create via the Command Line
 
Login via ssh to the first Proxmox VE node and run the following command:
 
Login via ssh to the first Proxmox VE node and run the following command:
 
  hp1# pvecm create CLUSTERNAME
 
  hp1# pvecm create CLUSTERNAME
 
To check the state of the new cluster use:
 
To check the state of the new cluster use:
 
  hp1# pvecm status
 
  hp1# pvecm status
Multiple Clusters In Same Network
+
Multiple Clusters in the Same Network
 
It is possible to create multiple clusters in the same physical or logical
 
It is possible to create multiple clusters in the same physical or logical
network. Each such cluster must have a unique name to avoid possible clashes in
+
network. In this case, each cluster must have a unique name to avoid possible
the cluster communication stack. This also helps avoid human confusion by making
+
clashes in the cluster communication stack. Furthermore, this helps avoid human
clusters clearly distinguishable.
+
confusion by making clusters clearly distinguishable.
 
While the bandwidth requirement of a corosync cluster is relatively low, the
 
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
 
latency of packages and the package per second (PPS) rate is the limiting
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A node that is about to be added to the cluster cannot hold any guests.
 
A node that is about to be added to the cluster cannot hold any guests.
 
All existing configuration in /etc/pve is overwritten when joining a cluster,
 
All existing configuration in /etc/pve is overwritten when joining a cluster,
since guest IDs could be conflicting. As a workaround create a backup of the
+
since guest IDs could otherwise conflict. As a workaround, you can create a
guest (vzdump) and restore it as a different ID after the node has been added
+
backup of the guest (vzdump) and restore it under a different ID, after the
to the cluster.
+
node has been added to the cluster.
 
Join Node to Cluster via GUI
 
Join Node to Cluster via GUI
Login to the web interface on an existing cluster node. Under Datacenter →
+
Log in to the web interface on an existing cluster node. Under Datacenter →
Cluster, click the button Join Information at the top. Then, click on the
+
Cluster, click the Join Information button at the top. Then, click on the
 
button Copy Information. Alternatively, copy the string from the Information
 
button Copy Information. Alternatively, copy the string from the Information
 
field manually.
 
field manually.
Next, login to the web interface on the node you want to add.
+
Next, log in to the web interface on the node you want to add.
 
Under Datacenter → Cluster, click on Join Cluster. Fill in the
 
Under Datacenter → Cluster, click on Join Cluster. Fill in the
 
Information field with the Join Information text you copied earlier.
 
Information field with the Join Information text you copied earlier.
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checkbox.
 
checkbox.
 
After clicking the Join button, the cluster join process will start
 
After clicking the Join button, the cluster join process will start
immediately. After the node joined the cluster its current node certificate
+
immediately. After the node has joined the cluster, its current node certificate
will be replaced by one signed from the cluster certificate authority (CA),
+
will be replaced by one signed from the cluster certificate authority (CA).
that means the current session will stop to work after a few seconds. You might
+
This means that the current session will stop working after a few seconds. You
then need to force-reload the webinterface and re-login with the cluster
+
then might need to force-reload the web interface and log in again with the
credentials.
+
cluster credentials.
 
Now your node should be visible under Datacenter → Cluster.
 
Now your node should be visible under Datacenter → Cluster.
 
Join Node to Cluster via Command Line
 
Join Node to Cluster via Command Line
Login via ssh to the node you want to join into an existing cluster.
+
Log in to the node you want to join into an existing cluster via ssh.
  hp2# pvecm add IP-ADDRESS-CLUSTER
+
  # pvecm add IP-ADDRESS-CLUSTER
For IP-ADDRESS-CLUSTER use the IP or hostname of an existing cluster node.
+
For IP-ADDRESS-CLUSTER, use the IP or hostname of an existing cluster node.
 
An IP address is recommended (see Link Address Types).
 
An IP address is recommended (see Link Address Types).
 
To check the state of the cluster use:
 
To check the state of the cluster use:
 
  # pvecm status
 
  # 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:          1/8
+
Ring ID:          1.1a8
 
Quorate:          Yes
 
Quorate:          Yes
 
Votequorum information
 
Votequorum 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 link0 parameter to set the nodes address on that network:
 
use the link0 parameter to set the nodes address on that network:
 
pvecm add IP-ADDRESS-CLUSTER -link0 LOCAL-IP-ADDRESS-LINK0
 
pvecm add IP-ADDRESS-CLUSTER -link0 LOCAL-IP-ADDRESS-LINK0
 
If you want to use the built-in redundancy of the
 
If you want to use the built-in redundancy of the
kronosnet transport layer, also use the link1 parameter.
+
Kronosnet transport layer, also use the link1 parameter.
Using the GUI, you can select the correct interface from the corresponding Link 0
+
Using the GUI, you can select the correct interface from the corresponding
and Link 1 fields in the Cluster Join dialog.
+
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
In the following example we will remove the node hp4 from the cluster.
+
any scheduled replication jobs to the node to be removed.
 +
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
 
Log in to a different cluster node (not hp4), and issue a pvecm nodes
 
command to identify the node ID to remove:
 
command to identify the node ID to remove:
hp1# pvecm nodes
+
hp1# pvecm nodes
 
Membership information
 
Membership information
 
~~~~~~~~~~~~~~~~~~~~~~
 
~~~~~~~~~~~~~~~~~~~~~~
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         3          1 hp3
 
         3          1 hp3
 
         4          1 hp4
 
         4          1 hp4
At this point you must power off hp4 and
+
At this point, you must power off hp4 and ensure that it will not power on
make sure that it will not power on again (in the network) as it
+
again (in the network) with its current configuration.
is.
+
As mentioned above, it is critical to power off the node
As said above, it is critical to power off the node
+
before removal, and make sure that it will not power on again
before removal, and make sure that it will never power on again
+
(in the existing cluster network) with its current configuration.
(in the existing cluster network) as it is.
+
If you power on the node as it is, the cluster could end up broken,
If you power on the node as it is, your cluster will be screwed up and
+
and it could be difficult to restore it to a functioning state.
it could be difficult to restore a clean cluster state.
 
 
After powering off the node hp4, we can safely remove it from the cluster.
 
After powering off the node hp4, we can safely remove it from the cluster.
 
  hp1# pvecm delnode hp4
 
  hp1# pvecm delnode hp4
 
  Killing node 4
 
  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
 
Use pvecm nodes or pvecm status to check the node list again. It should
 
look something like:
 
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:          1/8
 
Quorate:          Yes
 
 
Votequorum information
 
Votequorum information
 
~~~~~~~~~~~~~~~~~~~~~~
 
~~~~~~~~~~~~~~~~~~~~~~
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0x00000003          1 192.168.15.92
 
0x00000003          1 192.168.15.92
 
If, for whatever reason, you want this server to join the same cluster again,
 
If, for whatever reason, you want this server to join the same cluster again,
you have to
+
you have to:
reinstall Proxmox VE on it from scratch
+
do a fresh install of Proxmox VE on it,
 
then join it, as explained in the previous section.
 
then join it, as explained in the previous section.
 
After removal of the node, its SSH fingerprint will still reside in the
 
After removal of the node, its SSH fingerprint will still reside in the
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a node with the same IP or hostname, run pvecm updatecerts once on the
 
a node with the same IP or hostname, run pvecm updatecerts once on the
 
re-added node to update its fingerprint cluster wide.
 
re-added node to update its fingerprint cluster wide.
Separate A Node Without Reinstalling
+
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 storage locking doesn’t work over the cluster
 
storage with another cluster, as storage locking doesn’t work over the cluster
boundary. Further, it may also lead to VMID conflicts.
+
boundary. Furthermore, it may also lead to VMID conflicts.
Its suggested that you create a new storage where only the node which you want
+
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
 
to separate has access. This can be a new export on your NFS or a new Ceph
pool, to name a few examples. Its just important that the exact same storage
+
pool, to name a few examples. It’s just important that the exact same storage
does not gets accessed by multiple clusters. After setting this storage up move
+
does not get accessed by multiple clusters. After setting up this storage, move
all data from the node and its VMs to it. Then you are ready to separate the
+
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! Otherwise you will
+
Ensure that all shared resources are cleanly separated! Otherwise you
run into conflicts and problems.
+
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 -r /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 then 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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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 reliably 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
 
This needs a reliable network with latencies under 2 milliseconds (LAN
 
performance) to work properly. The network should not be used heavily by other
 
performance) to work properly. The network should not be used heavily by other
members, ideally corosync runs on its own network. Do not use a shared network
+
members; ideally corosync runs on its own network. Do not use a shared network
 
for corosync and storage (except as a potential low-priority fallback in a
 
for corosync and storage (except as a potential low-priority fallback in a
 
redundant configuration).
 
redundant configuration).
 
Before setting up a cluster, it is good practice to check if the network is fit
 
Before setting up a cluster, it is good practice to check if the network is fit
for that purpose. To make sure the nodes can connect to each other on the
+
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
 
cluster network, you can test the connectivity between them with the ping
 
tool.
 
tool.
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This is therefore not recommended.
 
This is therefore not recommended.
 
Separate Cluster Network
 
Separate Cluster Network
When creating a cluster without any parameters the corosync cluster network is
+
When creating a cluster without any parameters, the corosync cluster network is
generally shared with the Web UI and the VMs and their traffic. Depending on
+
generally shared with the web interface and the VMs' network. Depending on
your setup, even storage traffic may get sent over the same network. Its
+
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
+
recommended to change that, as corosync is a time-critical, real-time
 
application.
 
application.
Setting Up A New Network
+
Setting Up a New Network
 
First, you have to set up a new network interface. It should be on a physically
 
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
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Separate On Cluster Creation
 
Separate On Cluster Creation
 
This is possible via the linkX parameters of the pvecm create
 
This is possible via the linkX parameters of the pvecm create
command used for creating a new cluster.
+
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,
 
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 --link0 10.10.10.1
 
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
 
Afterwards, proceed as described above to
Line 331: Line 341:
 
You can do this 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.
Line 372: Line 382:
 
   }
 
   }
 
}
 
}
ringX_addr actually specifies a corosync link address, the name "ring"
+
ringX_addr actually specifies a corosync link address. The name "ring"
 
is a remnant of older corosync versions that is kept for backwards
 
is a remnant of older corosync versions that is kept for backwards
 
compatibility.
 
compatibility.
The first thing you want to do is add the name properties in the node entries
+
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.
 
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
 
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
 
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
+
hostnames, ensure that they are resolvable from all nodes (see also
Link Address Types)
+
Link Address Types).
In this example, we want to switch the cluster communication to the
+
In this example, we want to switch cluster communication to the
10.10.10.1/25 network. So we replace all ring0_addr respectively.
+
10.10.10.1/25 network, so we change the ring0_addr of each node respectively.
 
The exact same procedure can be used to change other ringX_addr values
 
The exact same procedure can be used to change other ringX_addr values
as well, although we recommend to not change multiple addresses at once, to make
+
as well. However, we recommend only changing one link address at a time, so
it easier to recover if something goes wrong.
+
that it’s easier to recover if something goes wrong.
 
After we increase the config_version property, the new configuration file
 
After we increase the config_version property, the new configuration file
 
should look like:
 
should look like:
Line 425: Line 435:
 
   }
 
   }
 
}
 
}
Then, after a final check if all changed information is correct, we save it and
+
Then, after a final check to see that all changed information is correct, we
once again follow the edit corosync.conf file
+
save it and once again follow the
section to bring it into effect.
+
edit corosync.conf file section to bring it into
 +
effect.
 
The changes will be applied live, so restarting corosync is not strictly
 
The changes will be applied live, so restarting corosync is not strictly
 
necessary. If you changed other settings as well, or notice corosync
 
necessary. If you changed other settings as well, or notice corosync
Line 433: Line 444:
 
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.
Corosync addresses
+
Corosync Addresses
 
A corosync link address (for backwards compatibility denoted by ringX_addr in
 
A corosync link address (for backwards compatibility denoted by ringX_addr in
 
corosync.conf) can be specified in two ways:
 
corosync.conf) can be specified in two ways:
IPv4/v6 addresses will be used directly. They are recommended, since they
+
IPv4/v6 addresses can be used directly. They are recommended, since they
 
are static and usually not changed carelessly.
 
are static and usually not changed carelessly.
Hostnames will be resolved using getaddrinfo, which means that per
+
Hostnames will be resolved using getaddrinfo, which means that by
 
default, IPv6 addresses will be used first, if available (see also
 
default, IPv6 addresses will be used first, if available (see also
 
man gai.conf). Keep this in mind, especially when upgrading an existing
 
man gai.conf). Keep this in mind, especially when upgrading an existing
 
cluster to IPv6.
 
cluster to IPv6.
Hostnames should be used with care, since the address they
+
Hostnames should be used with care, since the addresses they
 
resolve to can be changed without touching corosync or the node it runs on -
 
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
 
which may lead to a situation where an address is changed without thinking
Line 454: Line 465:
 
resolve all hostnames correctly.
 
resolve all hostnames correctly.
 
Since Proxmox VE 5.1, while supported, hostnames will be resolved at the time of
 
Since Proxmox VE 5.1, while supported, hostnames will be resolved at the time of
entry. Only the resolved IP is then saved to the configuration.
+
entry. Only the resolved IP is saved to the configuration.
 
Nodes that joined the cluster on earlier versions likely still use their
 
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
 
unresolved hostname in corosync.conf. It might be a good idea to replace
 
them with IPs or a separate hostname, as mentioned above.
 
them with IPs or a separate hostname, as mentioned above.
 
Corosync Redundancy
 
Corosync Redundancy
Corosync supports redundant networking via its integrated kronosnet layer by
+
Corosync supports redundant networking via its integrated Kronosnet layer by
 
default (it is not supported on the legacy udp/udpu transports). It can be
 
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
 
enabled by specifying more than one link address, either via the --linkX
Line 477: Line 488:
 
priority.
 
priority.
 
Even if all links are working, only the one with the highest priority will see
 
Even if all links are working, only the one with the highest priority will see
corosync traffic. Link priorities cannot be mixed, i.e. links with different
+
corosync traffic. Link priorities cannot be mixed, meaning that links with
priorities will not be able to communicate with each other.
+
different priorities will not be able to communicate with each other.
 
Since lower priority links will not see traffic unless all higher priorities
 
Since lower priority links will not see traffic unless all higher priorities
have failed, it becomes a useful strategy to specify even networks used for
+
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
+
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
+
worst, a higher latency or more congested connection might be better than no
 
connection at all.
 
connection at all.
 
Adding Redundant Links To An Existing Cluster
 
Adding Redundant Links To An Existing Cluster
Line 491: Line 502:
 
unique for each node.
 
unique for each node.
 
Lastly, add a new interface, as shown below, to your totem
 
Lastly, add a new interface, as shown below, to your totem
section, replacing X with your link number chosen above.
+
section, replacing X with the link number chosen above.
 
Assuming you added a link with number 1, the new configuration file could look
 
Assuming you added a link with number 1, the new configuration file could look
 
like this:
 
like this:
Line 553: Line 564:
 
B via a non-interactive SSH tunnel.
 
B via a non-interactive SSH tunnel.
 
VM and CT memory and local-storage migration in secure mode.
 
VM and CT memory and local-storage migration in secure mode.
During the migration one or more SSH tunnel(s) are established between the
+
During the migration, one or more SSH tunnel(s) are established between the
 
source and target nodes, in order to exchange migration information and
 
source and target nodes, in order to exchange migration information and
 
transfer memory and disk contents.
 
transfer memory and disk contents.
Line 561: Line 572:
 
login by the configured shell, ssh will automatically run it once the session
 
login by the configured shell, ssh will automatically run it once the session
 
is established successfully. This can cause some unexpected behavior, as those
 
is established successfully. This can cause some unexpected behavior, as those
commands may be executed with root permissions on any above described
+
commands may be executed with root permissions on any of the operations
operation. That can cause possible problematic side-effects!
+
described above. This can cause possible problematic side-effects!
 
In order to avoid such complications, it’s recommended to add a check in
 
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
 
/root/.bashrc to make sure the session is interactive, and only then run
Line 576: Line 587:
 
When configured, the cluster can sustain more node failures without
 
When configured, the cluster can sustain more node failures without
 
violating safety properties of the cluster communication.
 
violating safety properties of the cluster communication.
For this to work there are two services involved:
+
For this to work, there are two services involved:
a so called qdevice daemon which runs on each Proxmox VE node
+
A QDevice daemon which runs on each Proxmox VE node
an external vote daemon which runs on an independent server.
+
An external vote daemon which runs on an independent server
As a result you can achieve higher availability even in smaller setups (for
+
As a result, you can achieve higher availability, even in smaller setups (for
 
example 2+1 nodes).
 
example 2+1 nodes).
 
QDevice Technical Overview
 
QDevice Technical Overview
 
The Corosync Quorum Device (QDevice) is a daemon which runs on each cluster
 
The Corosync Quorum Device (QDevice) is a daemon which runs on each cluster
node. It provides a configured number of votes to the clusters quorum
+
node. It provides a configured number of votes to the cluster’s quorum
subsystem based on an external running third-party arbitrator’s decision.
+
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
 
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
 
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.
 
can see all nodes and thus choose only one set of nodes to give its vote.
This will only be done if said set of nodes can have quorum (again) when
+
This will only be done if said set of nodes can have quorum (again) after
 
receiving the third-party vote.
 
receiving the third-party vote.
Currently only QDevice Net is supported as a third-party arbitrator. It is
+
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
+
a daemon which provides a vote to a cluster partition, if it can reach the
partition members over the network. It will give only votes to one partition
+
partition members over the network. It will only give votes to one partition
 
of a cluster at any time.
 
of a cluster at any time.
 
It’s designed to support multiple clusters and is almost configuration and
 
It’s designed to support multiple clusters and is almost configuration and
 
state free. New clusters are handled dynamically and no configuration file
 
state free. New clusters are handled dynamically and no configuration file
 
is needed on the host running a QDevice.
 
is needed on the host running a QDevice.
The external host has the only requirement that it needs network access to the
+
The only requirements for the external host are that it needs network access to
cluster and a corosync-qnetd package available. We provide such a package
+
the cluster and to have a corosync-qnetd package available. We provide a package
for Debian based hosts, other Linux distributions should also have a package
+
for Debian based hosts, and other Linux distributions should also have a package
 
available through their respective package manager.
 
available through their respective package manager.
 
In contrast to corosync itself, a QDevice connects to the cluster over
 
In contrast to corosync itself, a QDevice connects to the cluster over
TCP/IP. The daemon may even run outside of the clusters LAN and can have longer
+
TCP/IP. The daemon may even run outside of the cluster’s LAN and can have longer
 
latencies than 2 ms.
 
latencies than 2 ms.
 
Supported Setups
 
Supported Setups
 
We support QDevices for clusters with an even number of nodes and recommend
 
We support QDevices for clusters with an even number of nodes and recommend
 
it for 2 node clusters, if they should provide higher availability.
 
it for 2 node clusters, if they should provide higher availability.
For clusters with an odd node count we discourage the use of QDevices
+
For clusters with an odd node count, we currently discourage the use of
currently. The reason for this, is the difference of the votes the QDevice
+
QDevices. The reason for this is the difference in the votes which the QDevice
provides for each cluster type. Even numbered clusters get single additional
+
provides for each cluster type. Even numbered clusters get a single additional
vote, with this we can only increase availability, i.e. if the QDevice
+
vote, which only increases availability, because if the QDevice
itself fails we are in the same situation as with no QDevice at all.
+
itself fails, you are in the same position as with no QDevice at all.
Now, with an odd numbered cluster size the QDevice provides (N-1) votes — where N corresponds to the cluster node count. This difference makes
+
On the other hand, with an odd numbered cluster size, the QDevice provides
sense, if we had only one additional vote the cluster can get into a split
+
(N-1) votes — where N corresponds to the cluster node count. This
brain situation.
+
alternative behavior makes sense; if it had only one additional vote, the
This algorithm would allow that all nodes but one (and naturally the
+
cluster could get into a split-brain situation. This algorithm allows for all
QDevice itself) could fail.
+
nodes but one (and naturally the QDevice itself) to fail. However, there are two
There are two drawbacks with this:
+
drawbacks to this:
 
If the QNet daemon itself fails, no other node may fail or the cluster
 
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
+
   immediately loses quorum. For example, in a cluster with 15 nodes, 7
 
   could fail before the cluster becomes inquorate. But, if a QDevice is
 
   could fail before the cluster becomes inquorate. But, if a QDevice is
   configured here and said QDevice fails itself no single node of
+
   configured here and it itself fails, no single node of the 15 may fail.
  the 15 may fail. The QDevice acts almost as a single point of failure in
+
  The QDevice acts almost as a single point of failure in this case.
  this case.
+
The fact that all but one node plus QDevice may fail sounds promising at
The fact that all but one node plus QDevice may fail sound promising at
+
   first, but this may result in a mass recovery of HA services, which could
   first, but this may result in a mass recovery of HA services that would
+
   overload the single remaining node. Furthermore, a Ceph server will stop
   overload the single node left. Also ceph server will stop to provide
+
   providing services if only ((N-1)/2) nodes or less remain online.
   services after only ((N-1)/2) nodes are online.
+
If you understand the drawbacks and implications, you can decide yourself if
If you understand the drawbacks and implications you can decide yourself if
+
you want to use this technology in an odd numbered cluster setup.
you should use this technology in an odd numbered cluster setup.
 
 
QDevice-Net Setup
 
QDevice-Net Setup
We recommend to run any daemon which provides votes to corosync-qdevice as an
+
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
 
unprivileged user. Proxmox VE and Debian provide a package which is already
 
configured to do so.
 
configured to do so.
 
The traffic between the daemon and the cluster must be encrypted to ensure a
 
The traffic between the daemon and the cluster must be encrypted to ensure a
safe and secure QDevice integration in Proxmox VE.
+
safe and secure integration of the QDevice in Proxmox VE.
 
First, install the corosync-qnetd package on your external server
 
First, install the corosync-qnetd package on your external server
 
external# apt install corosync-qnetd
 
external# apt install corosync-qnetd
 
and the corosync-qdevice package on all cluster nodes
 
and the corosync-qdevice package on all cluster nodes
 
pve# apt install corosync-qdevice
 
pve# apt install corosync-qdevice
After that, ensure that all your nodes on the cluster are online.
+
After doing this, ensure that all the nodes in the cluster are online.
You can now easily set up your QDevice by running the following command on one
+
You can now set up your QDevice by running the following command on one
 
of the Proxmox VE nodes:
 
of the Proxmox VE nodes:
 
pve# pvecm qdevice setup <QDEVICE-IP>
 
pve# pvecm qdevice setup <QDEVICE-IP>
Line 647: Line 657:
 
Make sure that the SSH configuration on your external server allows root
 
Make sure that the SSH configuration on your external server allows root
 
login via password, if you are asked for a password during this step.
 
login via password, if you are asked for a password during this step.
After you enter the password and all the steps are successfully completed, you
+
After you enter the password and all the steps have successfully completed, you
will see "Done". You can check the status now:
+
will see "Done". You can verify that the QDevice has been set up with:
 
pve# pvecm status
 
pve# pvecm status
 
...
 
...
Line 664: Line 674:
 
     0x00000002          1    A,V,NMW 192.168.22.181
 
     0x00000002          1    A,V,NMW 192.168.22.181
 
     0x00000000          1            Qdevice
 
     0x00000000          1            Qdevice
which means the QDevice is set up.
 
 
Frequently Asked Questions
 
Frequently Asked Questions
 
Tie Breaking
 
Tie Breaking
 
In case of a tie, where two same-sized cluster partitions cannot see each other
 
In case of a tie, where two same-sized cluster partitions cannot see each other
but the QDevice, the QDevice chooses randomly one of those partitions and
+
but can see the QDevice, the QDevice chooses one of those partitions randomly
provides a vote to it.
+
and provides a vote to it.
 
Possible Negative Implications
 
Possible Negative Implications
For clusters with an even node count there are no negative implications when
+
For clusters with an even node count, there are no negative implications when
setting up a QDevice. If it fails to work, you are as good as without QDevice at
+
using a QDevice. If it fails to work, it is the same as not having a QDevice
all.
+
at all.
 
Adding/Deleting Nodes After QDevice Setup
 
Adding/Deleting Nodes After QDevice Setup
 
If you want to add a new node or remove an existing one from a cluster with a
 
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
 
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,
 
remove nodes normally. Once you have a cluster with an even node count again,
you can set up the QDevice again as described above.
+
you can set up the QDevice again as described previously.
 
Removing the QDevice
 
Removing the QDevice
 
If you used the official pvecm tool to add the QDevice, you can remove it
 
If you used the official pvecm tool to add the QDevice, you can remove it
trivially by running:
+
by running:
 
pve# pvecm qdevice remove
 
pve# pvecm qdevice remove
 
Corosync Configuration
 
Corosync Configuration
Line 688: Line 697:
 
For further information 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.
Line 696: Line 705:
 
/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
effect immediately. 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 any Proxmox VE node 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 be 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 726: Line 736:
 
     '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 it is 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 link addresses for the kronosnet connections between
+
This names the different link addresses for the Kronosnet connections between
 
nodes.
 
nodes.
 
Cluster Cold Start
 
Cluster Cold Start
Line 753: Line 763:
 
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 Migration
 
Guest Migration
Line 761: Line 771:
 
datacenter.cfg or for a specific migration via API or command line
 
datacenter.cfg or for a specific migration via API or command line
 
parameters.
 
parameters.
It makes a difference if a Guest is online or offline, or if it has
+
It makes a difference if a guest is online or offline, or if it has
 
local resources (like a local disk).
 
local resources (like a local disk).
For Details about Virtual Machine Migration see the
+
For details about virtual machine migration, see the
 
QEMU/KVM Migration Chapter.
 
QEMU/KVM Migration Chapter.
For Details about Container Migration see the
+
For details about container migration, see the
 
Container Migration Chapter.
 
Container Migration Chapter.
 
Migration Type
 
Migration Type
Line 771: Line 781:
 
encrypted (secure) channel or an unencrypted (insecure) one.
 
encrypted (secure) channel or an unencrypted (insecure) one.
 
Setting the migration type to insecure means that the RAM content of a
 
Setting the migration type to insecure means that the RAM content of a
virtual guest gets also transferred unencrypted, which can lead to
+
virtual guest is also transferred unencrypted, which can lead to
 
information disclosure of critical data from inside the guest (for
 
information disclosure of critical data from inside the guest (for
example passwords or encryption keys).
+
example, passwords or encryption keys).
 
Therefore, we strongly recommend using the secure channel if you do
 
Therefore, we strongly recommend using the secure channel if you do
 
not have full control over the network and can not guarantee that no
 
not have full control over the network and can not guarantee that no
Line 783: Line 793:
 
modern systems is lower because they implement AES encryption in
 
modern systems is lower because they implement AES encryption in
 
hardware. The performance impact is particularly evident in fast
 
hardware. The performance impact is particularly evident in fast
networks where you can transfer 10 Gbps or more.
+
networks, where you can transfer 10 Gbps or more.
 
Migration Network
 
Migration Network
 
By default, Proxmox VE uses the network in which cluster communication
 
By default, Proxmox VE uses the network in which cluster communication
takes place to send the migration traffic. This is not optimal because
+
takes place to send the migration traffic. This is not optimal both because
 
sensitive cluster traffic can be disrupted and this network may not
 
sensitive cluster traffic can be disrupted and this network may not
 
have the best bandwidth available on the node.
 
have the best bandwidth available on the node.
 
Setting the migration network parameter allows the use of a dedicated
 
Setting the migration network parameter allows the use of a dedicated
network for the entire migration traffic. In addition to the memory,
+
network for all migration traffic. In addition to the memory,
 
this also affects the storage traffic for offline migrations.
 
this also affects the storage traffic for offline migrations.
The migration network is set as a network in the CIDR notation. This
+
The migration network is set as a network using CIDR notation. This
has the advantage that you do not have to set individual IP addresses
+
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
+
for each node. Proxmox VE can determine the real address on the
destination node from the network specified in the CIDR form. To
+
destination node from the network specified in the CIDR form. To
enable this, the network must be specified so that each node has one,
+
enable this, the network must be specified so that each node has exactly one
but only one IP in the respective network.
+
IP in the respective network.
 
Example
 
Example
We assume that we have a three-node setup with three separate
+
We assume that we have a three-node setup, with three separate
 
networks. One for public communication with the Internet, one for
 
networks. One for public communication with the Internet, one for
cluster communication and a very fast one, which we want to use as a
+
cluster communication, and a very fast one, which we want to use as a
 
dedicated network for migration.
 
dedicated network for migration.
 
A network configuration for such a setup might look as follows:
 
A network configuration for such a setup might look as follows:
Line 808: Line 818:
 
auto vmbr0
 
auto vmbr0
 
iface vmbr0 inet static
 
iface vmbr0 inet static
     address 192.X.Y.57
+
     address 192.X.Y.57/24
    netmask 255.255.250.0
 
 
     gateway 192.X.Y.1
 
     gateway 192.X.Y.1
 
     bridge-ports eno1
 
     bridge-ports eno1
Line 817: Line 826:
 
auto eno2
 
auto eno2
 
iface eno2 inet static
 
iface eno2 inet static
     address  10.1.1.1
+
     address  10.1.1.1/24
    netmask  255.255.255.0
 
 
# fast network
 
# fast network
 
auto eno3
 
auto eno3
 
iface eno3 inet static
 
iface eno3 inet static
     address  10.1.2.1
+
     address  10.1.2.1/24
    netmask  255.255.255.0
 
 
Here, we will use the network 10.1.2.0/24 as a migration network. For
 
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
 
a single migration, you can do this using the migration_network
Line 834: Line 841:
 
migration: secure,network=10.1.2.0/24
 
migration: secure,network=10.1.2.0/24
 
The migration type must always be set when the migration network
 
The migration type must always be set when the migration network
gets set in /etc/pve/datacenter.cfg.
+
is set in /etc/pve/datacenter.cfg.
 
</pvehide>
 
</pvehide>
 
<!--PVE_IMPORT_END_MARKER-->
 
<!--PVE_IMPORT_END_MARKER-->

Revision as of 11:27, 17 November 2021

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 5404 and 5405 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 A node that is about to be added to the cluster cannot hold any guests. All existing configuration in /etc/pve is overwritten when joining a cluster, since guest IDs could otherwise conflict. As a workaround, you can create a backup of the guest (vzdump) and restore it under a different ID, after the node has been added to the cluster.

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.

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 10.10.10.1/25 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

Important
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 that the SSH configuration on your external server allows root login via password, if you are asked for a password during this step. If you receive an error such as Host key verification failed. at this stage, running pvecm updatecerts could fix the issue.

After you enter the password and 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

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.