pvecm: explain role of ssh in PVE stack

[pve-docs.git] / pvecm.adoc

[[chapter_pvecm]]
ifdef::manvolnum[]
pvecm(1)
========
:pve-toplevel:

NAME
----

pvecm - Proxmox VE Cluster Manager

SYNOPSIS
--------

include::pvecm.1-synopsis.adoc[]

DESCRIPTION
-----------
endif::manvolnum[]

ifndef::manvolnum[]
Cluster Manager
===============
:pve-toplevel:
endif::manvolnum[]

The {PVE} cluster manager `pvecm` is a tool to create a group of
physical servers. Such a group is called a *cluster*. We use the
http://www.corosync.org[Corosync Cluster Engine] for reliable group
communication, and such clusters can consist of up to 32 physical nodes
(probably more, dependent on network latency).

`pvecm` can be used to create a new cluster, join nodes to a cluster,
leave the cluster, get status information and do various other cluster
related tasks. The **P**rox**m**o**x** **C**luster **F**ile **S**ystem (``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

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

* Easy migration of virtual machines and containers between physical
  hosts

* Fast deployment

* Cluster-wide services like firewall and HA


Requirements
------------

* All nodes must be able to connect to each other via UDP ports 5404 and 5405
 for corosync to work.

* Date and time have to be synchronized.

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

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

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

* Root password of a cluster node is required for adding nodes.

NOTE: It is not possible to mix {pve} 3.x and earlier with {pve} 4.X cluster
nodes.

NOTE: While it's possible to mix {pve} 4.4 and {pve} 5.0  nodes, doing so is
not supported as production configuration and should only used temporarily
during upgrading the whole cluster from one to another major version.

NOTE: Running a cluster of {pve} 6.x with earlier versions is not possible. The
cluster protocol (corosync) between {pve} 6.x and earlier versions changed
fundamentally. The corosync 3 packages for {pve} 5.4 are only intended for the
upgrade procedure to {pve} 6.0.


Preparing Nodes
---------------

First, install {PVE} 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 nodenames 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 the other with SSH via the easier to remember node name (see also
xref:pvecm_corosync_addresses[Link Address Types]). Note that we always
recommend to reference nodes by their IP addresses in the cluster configuration.


[[pvecm_create_cluster]]
Create a Cluster
----------------

You can either create a cluster on the console (login via `ssh`), or through
the API using the {pve} Webinterface (__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.

[[pvecm_cluster_create_via_gui]]
Create via Web GUI
~~~~~~~~~~~~~~~~~~

[thumbnail="screenshot/gui-cluster-create.png"]

Under __Datacenter -> Cluster__, click on *Create Cluster*. Enter the cluster
name and select a network connection from the dropdown to serve as the main
cluster network (Link 0). It defaults to the IP resolved via the node's
hostname.

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

NOTE: Ensure the network selected for the cluster communication is not used for
any high traffic loads like those of (network) storages or live-migration.
While the cluster network itself produces small amounts of data, it is very
sensitive to latency. Check out full
xref:pvecm_cluster_network_requirements[cluster network requirements].

[[pvecm_cluster_create_via_cli]]
Create via Command Line
~~~~~~~~~~~~~~~~~~~~~~~

Login via `ssh` to the first {pve} 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 Same Network
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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

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

[[pvecm_join_node_to_cluster]]
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 be conflicting. As a workaround create a backup of the
guest (`vzdump`) and restore it as a different ID after the node has been added
to the cluster.

Join Node to Cluster via GUI
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[thumbnail="screenshot/gui-cluster-join-information.png"]

Login to the web interface on an existing cluster node. Under __Datacenter ->
Cluster__, click the button *Join Information* at the top. Then, click on the
button *Copy Information*. Alternatively, copy the string from the 'Information'
field manually.

[thumbnail="screenshot/gui-cluster-join.png"]

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

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

Now your node should be visible under __Datacenter -> Cluster__.

Join Node to Cluster via Command Line
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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

----
 hp2# 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 xref:pvecm_corosync_addresses[Link Address Types]).


To check the state of the cluster use:

----
 # pvecm status
----

.Cluster status after adding 4 nodes
----
hp2# pvecm status
Quorum information
~~~~~~~~~~~~~~~~~~
Date:             Mon Apr 20 12:30:13 2015
Quorum provider:  corosync_votequorum
Nodes:            4
Node ID:          0x00000001
Ring ID:          1/8
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 the list of all nodes use:

----
 # pvecm nodes
----

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

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

[[pvecm_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
use the 'link0' parameter to set the nodes address on that network:

[source,bash]
----
pvecm add IP-ADDRESS-CLUSTER -link0 LOCAL-IP-ADDRESS-LINK0
----

If you want to use the built-in xref:pvecm_redundancy[redundancy] of the
kronosnet transport layer, also use the 'link1' parameter.

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

Remove a Cluster Node
---------------------

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

Move all virtual machines from the node. Make sure you have no local
data or backups you want to keep, or save them accordingly.
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
make sure that it will not power on again (in the network) as it
is.

IMPORTANT: As said above, it is critical to power off the node
*before* removal, and make sure that it will *never* power on again
(in the existing cluster network) as it is.
If you power on the node as it is, your cluster will be screwed up and
it could be difficult to restore a clean cluster state.

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

----
 hp1# pvecm delnode hp4
 Killing node 4
----

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

----
hp1# pvecm status

Quorum information
~~~~~~~~~~~~~~~~~~
Date:             Mon Apr 20 12:44:28 2015
Quorum provider:  corosync_votequorum
Nodes:            3
Node ID:          0x00000001
Ring ID:          1/8
Quorate:          Yes

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

* reinstall {pve} on it from scratch

* 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.

[[pvecm_separate_node_without_reinstall]]
Separate A Node Without Reinstalling
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

CAUTION: This is *not* the recommended method, proceed with caution. Use the
above mentioned method if you're unsure.

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

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

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

First, stop the corosync and the pve-cluster services on the node:
[source,bash]
----
systemctl stop pve-cluster
systemctl stop corosync
----

Start the cluster filesystem again in local mode:
[source,bash]
----
pmxcfs -l
----

Delete the corosync configuration files:
[source,bash]
----
rm /etc/pve/corosync.conf
rm -r /etc/corosync/*
----

You can now start the filesystem again as normal service:
[source,bash]
----
killall pmxcfs
systemctl start pve-cluster
----

The node is now separated from the cluster. You can deleted it from a remaining
node of the cluster with:
[source,bash]
----
pvecm delnode oldnode
----

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

And then repeat the 'pvecm delnode' command.

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

[source,bash]
----
rm /var/lib/corosync/*
----

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

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


Quorum
------

{pve} use a quorum-based technique to provide a consistent state among
all cluster nodes.

[quote, from Wikipedia, Quorum (distributed computing)]
____
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.
____

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: {pve} 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 {pve} 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`).

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

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

If the {pve} 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 {pve} 6.0).
Modern versions rely on https://kronosnet.org/[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 xref:pvecm_edit_corosync_conf[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 UI and the VMs and their traffic. Depending on
your setup, even storage traffic may get sent over the same network. Its
recommended to change that, as corosync is a time critical real time
application.

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
xref:pvecm_cluster_network_requirements[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:

[source,bash]
----
pvecm create test --link0 10.10.10.1
----

To check if everything is working properly execute:
[source,bash]
----
systemctl status corosync
----

Afterwards, proceed as described above to
xref:pvecm_adding_nodes_with_separated_cluster_network[add nodes with a separated cluster network].

[[pvecm_separate_cluster_net_after_creation]]
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 durations of quorum loss in the cluster, as nodes
have to restart corosync and come up one after the other on the new network.

Check how to xref:pvecm_edit_corosync_conf[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
xref:pvecm_corosync_addresses[Link Address Types])

In this example, we want to switch the cluster communication to the
10.10.10.1/25 network. So we replace all 'ring0_addr' respectively.

NOTE: 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
it 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 if all changed information is correct, we save it and
once again follow the xref:pvecm_edit_corosync_conf[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:

[source,bash]
----
systemctl restart corosync
----

Now check if everything is fine:

[source,bash]
----
systemctl status corosync
----

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

[[pvecm_corosync_addresses]]
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** will be used directly. They are recommended, since they
are static and usually not changed carelessly.

* **Hostnames** will be resolved using `getaddrinfo`, which means that per
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 address 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 {pve} 5.1, while supported, hostnames will be resolved at the time of
entry. Only the resolved IP is then saved to the configuration.

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


[[pvecm_redundancy]]
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, i.e. 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 even networks used for
other tasks (VMs, storage, etc...) as low-priority links. If worst comes to
worst, a higher-latency or more congested connection might be better than no
connection at all.

Adding Redundant Links To An Existing Cluster
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To add a new link to a running configuration, first check how to
xref:pvecm_edit_corosync_conf[edit the corosync.conf file].

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

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

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

----
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
xref:pvecm_edit_corosync_conf[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 {PVE} Clustering
-------------------------------

{PVE} utilizes SSH tunnels for various operations:

* Proxying terminal sessions on the GUI

* VM/CT Migrations (if not configured 'insecure' mode)

* Storage replications

For example when you connect another nodes shell through the interface, a
non-interactive SSH tunnel is started in order to forward the necessary ports
for the VNC connection.

Similarly during a VM migration an SSH tunnel is established between the target
and source nodes. This way the local `qemu` socket can be used for the migration.

IMPORTANT: In case you have a custom `.bashrc` or similar file that gets
executed on login, `ssh` will automatically run it once the session is
established. This can cause some unexpected behavior (as commands may be
executed as a side-effect).

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:

----
# If not running interactively, don't do anything
case $- in
    *i*) ;;
      *) return;;
esac
----


Corosync External Vote Support
------------------------------

This section describes a way to deploy an external voter in a {pve} 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 so called qdevice daemon which runs on each {pve} 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 clusters quorum
subsystem based on an external running third-party arbitrator's decision.
Its primary use is to allow a cluster to sustain more node failures than
standard quorum rules allow. This can be done safely as the external device
can see all nodes and thus choose only one set of nodes to give its vote.
This will only be done if said set of nodes can have quorum (again) when
receiving the third-party vote.

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

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

NOTE: 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
latencies than 2 ms.

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 discourage the use of QDevices
currently. The reason for this, is the difference of the votes the QDevice
provides for each cluster type. Even numbered clusters get single additional
vote, with this we can only increase availability, i.e. if the QDevice
itself fails we are in the same situation as with no QDevice at all.

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

* If 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 said QDevice fails itself **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 sound promising at
  first, but this may result in a mass recovery of HA services that would
  overload the single node left. Also ceph server will stop to provide
  services after only '((N-1)/2)' nodes are online.

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

QDevice-Net Setup
~~~~~~~~~~~~~~~~~

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

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

You can now easily set up your QDevice by running the following command on one
of the {pve} 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.

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

----
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

----

which means the QDevice is set up.

Frequently Asked Questions
~~~~~~~~~~~~~~~~~~~~~~~~~~

Tie Breaking
^^^^^^^^^^^^

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
provides a vote to it.

Possible Negative Implications
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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
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 above.

Removing the QDevice
^^^^^^^^^^^^^^^^^^^^

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

----
pve# pvecm qdevice remove
----

//Still TODO
//^^^^^^^^^^
//There is still stuff to add here


Corosync Configuration
----------------------

The `/etc/pve/corosync.conf` file plays a central role in a {pve} cluster. It
controls the cluster membership and its network.
For further information about it, check the corosync.conf man page:
[source,bash]
----
man corosync.conf
----

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

[[pvecm_edit_corosync_conf]]
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 changes which can be integrated in a running corosync will take
effect immediately. So you should always make a copy and edit that instead, to
avoid triggering some unwanted changes by an in-between safe.

[source,bash]
----
cp /etc/pve/corosync.conf /etc/pve/corosync.conf.new
----

Then open the config file with your favorite editor, `nano` and `vim.tiny` are
preinstalled on any {pve} node for example.

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

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

[source,bash]
----
cp /etc/pve/corosync.conf /etc/pve/corosync.conf.bak
----

Then move the new configuration file over the old one:
[source,bash]
----
mv /etc/pve/corosync.conf.new /etc/pve/corosync.conf
----

You may check with the commands
[source,bash]
----
systemctl status corosync
journalctl -b -u corosync
----

If the change could be applied automatically. If not you may have to restart the
corosync service via:
[source,bash]
----
systemctl restart corosync
----

On errors check the troubleshooting section below.

Troubleshooting
~~~~~~~~~~~~~~~

Issue: 'quorum.expected_votes must be configured'
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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

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

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

Write Configuration When Not Quorate
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If you need to change '/etc/pve/corosync.conf' on an node with no quorum, and you
know what you do, use:
[source,bash]
----
pvecm expected 1
----

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

This is not enough if corosync cannot start anymore. Here 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 brains. If you are not sure what went wrong
it's best to ask the Proxmox Community to help you.


[[pvecm_corosync_conf_glossary]]
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 boots faster than others. Please keep in
mind that guest startup is delayed until you reach quorum.


Guest Migration
---------------

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

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
xref:qm_migration[QEMU/KVM Migration Chapter].

For Details about Container Migration see the
xref:pct_migration[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 gets also transferred unencrypted, which can lead to
information disclosure of critical data from inside the guest (for
example passwords or encryption keys).

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

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

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

Migration Network
~~~~~~~~~~~~~~~~~

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

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

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

Example
^^^^^^^

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

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

----
iface eno1 inet manual

# public network
auto vmbr0
iface vmbr0 inet static
    address 192.X.Y.57
    netmask 255.255.250.0
    gateway 192.X.Y.1
    bridge-ports eno1
    bridge-stp off
    bridge-fd 0

# cluster network
auto eno2
iface eno2 inet static
    address  10.1.1.1
    netmask  255.255.255.0

# fast network
auto eno3
iface eno3 inet static
    address  10.1.2.1
    netmask  255.255.255.0
----

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

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

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

----
# use dedicated migration network
migration: secure,network=10.1.2.0/24
----

NOTE: The migration type must always be set when the migration network
gets set in `/etc/pve/datacenter.cfg`.


ifdef::manvolnum[]
include::pve-copyright.adoc[]
endif::manvolnum[]