Requirements
------------
-* 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 5405-5412
for corosync to work.
* Date and time must be synchronized.
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.
+CAUTION: All existing configuration in `/etc/pve` is overwritten when joining a
+cluster. In particular, a joining node cannot hold any guests, since guest IDs
+could otherwise conflict, and the node will inherit the cluster's storage
+configuration. To join a node with existing guest, as a workaround, you can
+create a backup of each guest (using `vzdump`) and restore it under a different
+ID after joining. If the node's storage layout differs, you will need to re-add
+the node's storages, and adapt each storage's node restriction to reflect on
+which nodes the storage is actually available.
Join Node to Cluster via GUI
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[source,bash]
----
-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 xref:pvecm_redundancy[redundancy] of the
[[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).
+
+The {pve} 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 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 ensure that the nodes can connect to each other on the
for Debian based hosts, and 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 cluster's LAN and can have longer
-latencies than 2 ms.
+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
~~~~~~~~~~~~~~~~
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:
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
+ 0x00000001 1 A,V,NMW 192.168.22.180 (local)
+ 0x00000002 1 A,V,NMW 192.168.22.181
+ 0x00000000 1 Qdevice
----
+[[pvecm_qdevice_status_flags]]
+QDevice Status Flags
+^^^^^^^^^^^^^^^^^^^^
+
+The status output of the QDevice, as seen above, will usually contain three
+columns:
+
+* `A` / `NA`: Alive or Not Alive. Indicates if the communication to the external
+ `corosync-qndetd` daemon works.
+* `V` / `NV`: If the QDevice will cast a vote for the node. In a split-brain
+ situation, where the corosync connection between the nodes is down, but they
+ both can still communicate with the external `corosync-qnetd` daemon,
+ only one node will get the vote.
+* `MW` / `NMW`: Master wins (`MV`) or not (`NMW`). Default is `NMW`, see
+ footnote:[`votequorum_qdevice_master_wins` manual page
+ https://manpages.debian.org/bookworm/libvotequorum-dev/votequorum_qdevice_master_wins.3.en.html].
+* `NR`: QDevice is not registered.
+
Frequently Asked Questions
~~~~~~~~~~~~~~~~~~~~~~~~~~
mind that guest startup is delayed until you reach quorum.
+[[pvecm_next_id_range]]
+Guest VMID Auto-Selection
+------------------------
+
+When creating new guests the web interface will ask the backend for a free VMID
+automatically. The default range for searching is `100` to `1000000` (lower
+than the maximal allowed VMID enforced by the schema).
+
+Sometimes admins either want to allocate new VMIDs in a separate range, for
+example to easily separate temporary VMs with ones that choose a VMID manually.
+Other times its just desired to provided a stable length VMID, for which
+setting the lower boundary to, for example, `100000` gives much more room for.
+
+To accommodate this use case one can set either lower, upper or both boundaries
+via the `datacenter.cfg` configuration file, which can be edited in the web
+interface under 'Datacenter' -> 'Options'.
+
+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
+`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
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:
+parameter of the command-line tool:
----
# qm migrate 106 tre --online --migration_network 10.1.2.0/24
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