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1 [[chapter_pvecm]]
2 ifdef::manvolnum[]
3 pvecm(1)
4 ========
5 :pve-toplevel:
6
7 NAME
8 ----
9
10 pvecm - Proxmox VE Cluster Manager
11
12 SYNOPSIS
13 --------
14
15 include::pvecm.1-synopsis.adoc[]
16
17 DESCRIPTION
18 -----------
19 endif::manvolnum[]
20
21 ifndef::manvolnum[]
22 Cluster Manager
23 ===============
24 :pve-toplevel:
25 endif::manvolnum[]
26
27 The {pve} cluster manager `pvecm` is a tool to create a group of
28 physical servers. Such a group is called a *cluster*. We use the
29 http://www.corosync.org[Corosync Cluster Engine] for reliable group
30 communication. There's no explicit limit for the number of nodes in a cluster.
31 In practice, the actual possible node count may be limited by the host and
32 network performance. Currently (2021), there are reports of clusters (using
33 high-end enterprise hardware) with over 50 nodes in production.
34
35 `pvecm` can be used to create a new cluster, join nodes to a cluster,
36 leave the cluster, get status information, and do various other cluster-related
37 tasks. The **P**rox**m**o**x** **C**luster **F**ile **S**ystem (``pmxcfs'')
38 is used to transparently distribute the cluster configuration to all cluster
39 nodes.
40
41 Grouping nodes into a cluster has the following advantages:
42
43 * Centralized, web-based management
44
45 * Multi-master clusters: each node can do all management tasks
46
47 * Use of `pmxcfs`, a database-driven file system, for storing configuration
48 files, replicated in real-time on all nodes using `corosync`
49
50 * Easy migration of virtual machines and containers between physical
51 hosts
52
53 * Fast deployment
54
55 * Cluster-wide services like firewall and HA
56
57
58 Requirements
59 ------------
60
61 * All nodes must be able to connect to each other via UDP ports 5404 and 5405
62 for corosync to work.
63
64 * Date and time must be synchronized.
65
66 * An SSH tunnel on TCP port 22 between nodes is required.
67
68 * If you are interested in High Availability, you need to have at
69 least three nodes for reliable quorum. All nodes should have the
70 same version.
71
72 * We recommend a dedicated NIC for the cluster traffic, especially if
73 you use shared storage.
74
75 * The root password of a cluster node is required for adding nodes.
76
77 * Online migration of virtual machines is only supported when nodes have CPUs
78 from the same vendor. It might work otherwise, but this is never guaranteed.
79
80 NOTE: It is not possible to mix {pve} 3.x and earlier with {pve} 4.X cluster
81 nodes.
82
83 NOTE: While it's possible to mix {pve} 4.4 and {pve} 5.0 nodes, doing so is
84 not supported as a production configuration and should only be done temporarily,
85 during an upgrade of the whole cluster from one major version to another.
86
87 NOTE: Running a cluster of {pve} 6.x with earlier versions is not possible. The
88 cluster protocol (corosync) between {pve} 6.x and earlier versions changed
89 fundamentally. The corosync 3 packages for {pve} 5.4 are only intended for the
90 upgrade procedure to {pve} 6.0.
91
92
93 Preparing Nodes
94 ---------------
95
96 First, install {pve} on all nodes. Make sure that each node is
97 installed with the final hostname and IP configuration. Changing the
98 hostname and IP is not possible after cluster creation.
99
100 While it's common to reference all node names and their IPs in `/etc/hosts` (or
101 make their names resolvable through other means), this is not necessary for a
102 cluster to work. It may be useful however, as you can then connect from one node
103 to another via SSH, using the easier to remember node name (see also
104 xref:pvecm_corosync_addresses[Link Address Types]). Note that we always
105 recommend referencing nodes by their IP addresses in the cluster configuration.
106
107
108 [[pvecm_create_cluster]]
109 Create a Cluster
110 ----------------
111
112 You can either create a cluster on the console (login via `ssh`), or through
113 the API using the {pve} web interface (__Datacenter -> Cluster__).
114
115 NOTE: Use a unique name for your cluster. This name cannot be changed later.
116 The cluster name follows the same rules as node names.
117
118 [[pvecm_cluster_create_via_gui]]
119 Create via Web GUI
120 ~~~~~~~~~~~~~~~~~~
121
122 [thumbnail="screenshot/gui-cluster-create.png"]
123
124 Under __Datacenter -> Cluster__, click on *Create Cluster*. Enter the cluster
125 name and select a network connection from the drop-down list to serve as the
126 main cluster network (Link 0). It defaults to the IP resolved via the node's
127 hostname.
128
129 As of {pve} 6.2, up to 8 fallback links can be added to a cluster. To add a
130 redundant link, click the 'Add' button and select a link number and IP address
131 from the respective fields. Prior to {pve} 6.2, to add a second link as
132 fallback, you can select the 'Advanced' checkbox and choose an additional
133 network interface (Link 1, see also xref:pvecm_redundancy[Corosync Redundancy]).
134
135 NOTE: Ensure that the network selected for cluster communication is not used for
136 any high traffic purposes, like network storage or live-migration.
137 While the cluster network itself produces small amounts of data, it is very
138 sensitive to latency. Check out full
139 xref:pvecm_cluster_network_requirements[cluster network requirements].
140
141 [[pvecm_cluster_create_via_cli]]
142 Create via the Command Line
143 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
144
145 Login via `ssh` to the first {pve} node and run the following command:
146
147 ----
148 hp1# pvecm create CLUSTERNAME
149 ----
150
151 To check the state of the new cluster use:
152
153 ----
154 hp1# pvecm status
155 ----
156
157 Multiple Clusters in the Same Network
158 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
159
160 It is possible to create multiple clusters in the same physical or logical
161 network. In this case, each cluster must have a unique name to avoid possible
162 clashes in the cluster communication stack. Furthermore, this helps avoid human
163 confusion by making clusters clearly distinguishable.
164
165 While the bandwidth requirement of a corosync cluster is relatively low, the
166 latency of packages and the package per second (PPS) rate is the limiting
167 factor. Different clusters in the same network can compete with each other for
168 these resources, so it may still make sense to use separate physical network
169 infrastructure for bigger clusters.
170
171 [[pvecm_join_node_to_cluster]]
172 Adding Nodes to the Cluster
173 ---------------------------
174
175 CAUTION: A node that is about to be added to the cluster cannot hold any guests.
176 All existing configuration in `/etc/pve` is overwritten when joining a cluster,
177 since guest IDs could otherwise conflict. As a workaround, you can create a
178 backup of the guest (`vzdump`) and restore it under a different ID, after the
179 node has been added to the cluster.
180
181 Join Node to Cluster via GUI
182 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
183
184 [thumbnail="screenshot/gui-cluster-join-information.png"]
185
186 Log in to the web interface on an existing cluster node. Under __Datacenter ->
187 Cluster__, click the *Join Information* button at the top. Then, click on the
188 button *Copy Information*. Alternatively, copy the string from the 'Information'
189 field manually.
190
191 [thumbnail="screenshot/gui-cluster-join.png"]
192
193 Next, log in to the web interface on the node you want to add.
194 Under __Datacenter -> Cluster__, click on *Join Cluster*. Fill in the
195 'Information' field with the 'Join Information' text you copied earlier.
196 Most settings required for joining the cluster will be filled out
197 automatically. For security reasons, the cluster password has to be entered
198 manually.
199
200 NOTE: To enter all required data manually, you can disable the 'Assisted Join'
201 checkbox.
202
203 After clicking the *Join* button, the cluster join process will start
204 immediately. After the node has joined the cluster, its current node certificate
205 will be replaced by one signed from the cluster certificate authority (CA).
206 This means that the current session will stop working after a few seconds. You
207 then might need to force-reload the web interface and log in again with the
208 cluster credentials.
209
210 Now your node should be visible under __Datacenter -> Cluster__.
211
212 Join Node to Cluster via Command Line
213 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
214
215 Log in to the node you want to join into an existing cluster via `ssh`.
216
217 ----
218 # pvecm add IP-ADDRESS-CLUSTER
219 ----
220
221 For `IP-ADDRESS-CLUSTER`, use the IP or hostname of an existing cluster node.
222 An IP address is recommended (see xref:pvecm_corosync_addresses[Link Address Types]).
223
224
225 To check the state of the cluster use:
226
227 ----
228 # pvecm status
229 ----
230
231 .Cluster status after adding 4 nodes
232 ----
233 # pvecm status
234 Cluster information
235 ~~~~~~~~~~~~~~~~~~~
236 Name: prod-central
237 Config Version: 3
238 Transport: knet
239 Secure auth: on
240
241 Quorum information
242 ~~~~~~~~~~~~~~~~~~
243 Date: Tue Sep 14 11:06:47 2021
244 Quorum provider: corosync_votequorum
245 Nodes: 4
246 Node ID: 0x00000001
247 Ring ID: 1.1a8
248 Quorate: Yes
249
250 Votequorum information
251 ~~~~~~~~~~~~~~~~~~~~~~
252 Expected votes: 4
253 Highest expected: 4
254 Total votes: 4
255 Quorum: 3
256 Flags: Quorate
257
258 Membership information
259 ~~~~~~~~~~~~~~~~~~~~~~
260 Nodeid Votes Name
261 0x00000001 1 192.168.15.91
262 0x00000002 1 192.168.15.92 (local)
263 0x00000003 1 192.168.15.93
264 0x00000004 1 192.168.15.94
265 ----
266
267 If you only want a list of all nodes, use:
268
269 ----
270 # pvecm nodes
271 ----
272
273 .List nodes in a cluster
274 ----
275 # pvecm nodes
276
277 Membership information
278 ~~~~~~~~~~~~~~~~~~~~~~
279 Nodeid Votes Name
280 1 1 hp1
281 2 1 hp2 (local)
282 3 1 hp3
283 4 1 hp4
284 ----
285
286 [[pvecm_adding_nodes_with_separated_cluster_network]]
287 Adding Nodes with Separated Cluster Network
288 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
289
290 When adding a node to a cluster with a separated cluster network, you need to
291 use the 'link0' parameter to set the nodes address on that network:
292
293 [source,bash]
294 ----
295 pvecm add IP-ADDRESS-CLUSTER -link0 LOCAL-IP-ADDRESS-LINK0
296 ----
297
298 If you want to use the built-in xref:pvecm_redundancy[redundancy] of the
299 Kronosnet transport layer, also use the 'link1' parameter.
300
301 Using the GUI, you can select the correct interface from the corresponding
302 'Link X' fields in the *Cluster Join* dialog.
303
304 Remove a Cluster Node
305 ---------------------
306
307 CAUTION: Read the procedure carefully before proceeding, as it may
308 not be what you want or need.
309
310 Move all virtual machines from the node. Ensure that you have made copies of any
311 local data or backups that you want to keep. In addition, make sure to remove
312 any scheduled replication jobs to the node to be removed.
313
314 CAUTION: Failure to remove replication jobs to a node before removing said node
315 will result in the replication job becoming irremovable. Especially note that
316 replication automatically switches direction if a replicated VM is migrated, so
317 by migrating a replicated VM from a node to be deleted, replication jobs will be
318 set up to that node automatically.
319
320 In the following example, we will remove the node hp4 from the cluster.
321
322 Log in to a *different* cluster node (not hp4), and issue a `pvecm nodes`
323 command to identify the node ID to remove:
324
325 ----
326 hp1# pvecm nodes
327
328 Membership information
329 ~~~~~~~~~~~~~~~~~~~~~~
330 Nodeid Votes Name
331 1 1 hp1 (local)
332 2 1 hp2
333 3 1 hp3
334 4 1 hp4
335 ----
336
337
338 At this point, you must power off hp4 and ensure that it will not power on
339 again (in the network) with its current configuration.
340
341 IMPORTANT: As mentioned above, it is critical to power off the node
342 *before* removal, and make sure that it will *not* power on again
343 (in the existing cluster network) with its current configuration.
344 If you power on the node as it is, the cluster could end up broken,
345 and it could be difficult to restore it to a functioning state.
346
347 After powering off the node hp4, we can safely remove it from the cluster.
348
349 ----
350 hp1# pvecm delnode hp4
351 Killing node 4
352 ----
353
354 NOTE: At this point, it is possible that you will receive an error message
355 stating `Could not kill node (error = CS_ERR_NOT_EXIST)`. This does not
356 signify an actual failure in the deletion of the node, but rather a failure in
357 corosync trying to kill an offline node. Thus, it can be safely ignored.
358
359 Use `pvecm nodes` or `pvecm status` to check the node list again. It should
360 look something like:
361
362 ----
363 hp1# pvecm status
364
365 ...
366
367 Votequorum information
368 ~~~~~~~~~~~~~~~~~~~~~~
369 Expected votes: 3
370 Highest expected: 3
371 Total votes: 3
372 Quorum: 2
373 Flags: Quorate
374
375 Membership information
376 ~~~~~~~~~~~~~~~~~~~~~~
377 Nodeid Votes Name
378 0x00000001 1 192.168.15.90 (local)
379 0x00000002 1 192.168.15.91
380 0x00000003 1 192.168.15.92
381 ----
382
383 If, for whatever reason, you want this server to join the same cluster again,
384 you have to:
385
386 * do a fresh install of {pve} on it,
387
388 * then join it, as explained in the previous section.
389
390 NOTE: After removal of the node, its SSH fingerprint will still reside in the
391 'known_hosts' of the other nodes. If you receive an SSH error after rejoining
392 a node with the same IP or hostname, run `pvecm updatecerts` once on the
393 re-added node to update its fingerprint cluster wide.
394
395 [[pvecm_separate_node_without_reinstall]]
396 Separate a Node Without Reinstalling
397 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
398
399 CAUTION: This is *not* the recommended method, proceed with caution. Use the
400 previous method if you're unsure.
401
402 You can also separate a node from a cluster without reinstalling it from
403 scratch. But after removing the node from the cluster, it will still have
404 access to any shared storage. This must be resolved before you start removing
405 the node from the cluster. A {pve} cluster cannot share the exact same
406 storage with another cluster, as storage locking doesn't work over the cluster
407 boundary. Furthermore, it may also lead to VMID conflicts.
408
409 It's suggested that you create a new storage, where only the node which you want
410 to separate has access. This can be a new export on your NFS or a new Ceph
411 pool, to name a few examples. It's just important that the exact same storage
412 does not get accessed by multiple clusters. After setting up this storage, move
413 all data and VMs from the node to it. Then you are ready to separate the
414 node from the cluster.
415
416 WARNING: Ensure that all shared resources are cleanly separated! Otherwise you
417 will run into conflicts and problems.
418
419 First, stop the corosync and pve-cluster services on the node:
420 [source,bash]
421 ----
422 systemctl stop pve-cluster
423 systemctl stop corosync
424 ----
425
426 Start the cluster file system again in local mode:
427 [source,bash]
428 ----
429 pmxcfs -l
430 ----
431
432 Delete the corosync configuration files:
433 [source,bash]
434 ----
435 rm /etc/pve/corosync.conf
436 rm -r /etc/corosync/*
437 ----
438
439 You can now start the file system again as a normal service:
440 [source,bash]
441 ----
442 killall pmxcfs
443 systemctl start pve-cluster
444 ----
445
446 The node is now separated from the cluster. You can deleted it from any
447 remaining node of the cluster with:
448 [source,bash]
449 ----
450 pvecm delnode oldnode
451 ----
452
453 If the command fails due to a loss of quorum in the remaining node, you can set
454 the expected votes to 1 as a workaround:
455 [source,bash]
456 ----
457 pvecm expected 1
458 ----
459
460 And then repeat the 'pvecm delnode' command.
461
462 Now switch back to the separated node and delete all the remaining cluster
463 files on it. This ensures that the node can be added to another cluster again
464 without problems.
465
466 [source,bash]
467 ----
468 rm /var/lib/corosync/*
469 ----
470
471 As the configuration files from the other nodes are still in the cluster
472 file system, you may want to clean those up too. After making absolutely sure
473 that you have the correct node name, you can simply remove the entire
474 directory recursively from '/etc/pve/nodes/NODENAME'.
475
476 CAUTION: The node's SSH keys will remain in the 'authorized_key' file. This
477 means that the nodes can still connect to each other with public key
478 authentication. You should fix this by removing the respective keys from the
479 '/etc/pve/priv/authorized_keys' file.
480
481
482 Quorum
483 ------
484
485 {pve} use a quorum-based technique to provide a consistent state among
486 all cluster nodes.
487
488 [quote, from Wikipedia, Quorum (distributed computing)]
489 ____
490 A quorum is the minimum number of votes that a distributed transaction
491 has to obtain in order to be allowed to perform an operation in a
492 distributed system.
493 ____
494
495 In case of network partitioning, state changes requires that a
496 majority of nodes are online. The cluster switches to read-only mode
497 if it loses quorum.
498
499 NOTE: {pve} assigns a single vote to each node by default.
500
501
502 Cluster Network
503 ---------------
504
505 The cluster network is the core of a cluster. All messages sent over it have to
506 be delivered reliably to all nodes in their respective order. In {pve} this
507 part is done by corosync, an implementation of a high performance, low overhead,
508 high availability development toolkit. It serves our decentralized configuration
509 file system (`pmxcfs`).
510
511 [[pvecm_cluster_network_requirements]]
512 Network Requirements
513 ~~~~~~~~~~~~~~~~~~~~
514 This needs a reliable network with latencies under 2 milliseconds (LAN
515 performance) to work properly. The network should not be used heavily by other
516 members; ideally corosync runs on its own network. Do not use a shared network
517 for corosync and storage (except as a potential low-priority fallback in a
518 xref:pvecm_redundancy[redundant] configuration).
519
520 Before setting up a cluster, it is good practice to check if the network is fit
521 for that purpose. To ensure that the nodes can connect to each other on the
522 cluster network, you can test the connectivity between them with the `ping`
523 tool.
524
525 If the {pve} firewall is enabled, ACCEPT rules for corosync will automatically
526 be generated - no manual action is required.
527
528 NOTE: Corosync used Multicast before version 3.0 (introduced in {pve} 6.0).
529 Modern versions rely on https://kronosnet.org/[Kronosnet] for cluster
530 communication, which, for now, only supports regular UDP unicast.
531
532 CAUTION: You can still enable Multicast or legacy unicast by setting your
533 transport to `udp` or `udpu` in your xref:pvecm_edit_corosync_conf[corosync.conf],
534 but keep in mind that this will disable all cryptography and redundancy support.
535 This is therefore not recommended.
536
537 Separate Cluster Network
538 ~~~~~~~~~~~~~~~~~~~~~~~~
539
540 When creating a cluster without any parameters, the corosync cluster network is
541 generally shared with the web interface and the VMs' network. Depending on
542 your setup, even storage traffic may get sent over the same network. It's
543 recommended to change that, as corosync is a time-critical, real-time
544 application.
545
546 Setting Up a New Network
547 ^^^^^^^^^^^^^^^^^^^^^^^^
548
549 First, you have to set up a new network interface. It should be on a physically
550 separate network. Ensure that your network fulfills the
551 xref:pvecm_cluster_network_requirements[cluster network requirements].
552
553 Separate On Cluster Creation
554 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
555
556 This is possible via the 'linkX' parameters of the 'pvecm create'
557 command, used for creating a new cluster.
558
559 If you have set up an additional NIC with a static address on 10.10.10.1/25,
560 and want to send and receive all cluster communication over this interface,
561 you would execute:
562
563 [source,bash]
564 ----
565 pvecm create test --link0 10.10.10.1
566 ----
567
568 To check if everything is working properly, execute:
569 [source,bash]
570 ----
571 systemctl status corosync
572 ----
573
574 Afterwards, proceed as described above to
575 xref:pvecm_adding_nodes_with_separated_cluster_network[add nodes with a separated cluster network].
576
577 [[pvecm_separate_cluster_net_after_creation]]
578 Separate After Cluster Creation
579 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
580
581 You can do this if you have already created a cluster and want to switch
582 its communication to another network, without rebuilding the whole cluster.
583 This change may lead to short periods of quorum loss in the cluster, as nodes
584 have to restart corosync and come up one after the other on the new network.
585
586 Check how to xref:pvecm_edit_corosync_conf[edit the corosync.conf file] first.
587 Then, open it and you should see a file similar to:
588
589 ----
590 logging {
591 debug: off
592 to_syslog: yes
593 }
594
595 nodelist {
596
597 node {
598 name: due
599 nodeid: 2
600 quorum_votes: 1
601 ring0_addr: due
602 }
603
604 node {
605 name: tre
606 nodeid: 3
607 quorum_votes: 1
608 ring0_addr: tre
609 }
610
611 node {
612 name: uno
613 nodeid: 1
614 quorum_votes: 1
615 ring0_addr: uno
616 }
617
618 }
619
620 quorum {
621 provider: corosync_votequorum
622 }
623
624 totem {
625 cluster_name: testcluster
626 config_version: 3
627 ip_version: ipv4-6
628 secauth: on
629 version: 2
630 interface {
631 linknumber: 0
632 }
633
634 }
635 ----
636
637 NOTE: `ringX_addr` actually specifies a corosync *link address*. The name "ring"
638 is a remnant of older corosync versions that is kept for backwards
639 compatibility.
640
641 The first thing you want to do is add the 'name' properties in the node entries,
642 if you do not see them already. Those *must* match the node name.
643
644 Then replace all addresses from the 'ring0_addr' properties of all nodes with
645 the new addresses. You may use plain IP addresses or hostnames here. If you use
646 hostnames, ensure that they are resolvable from all nodes (see also
647 xref:pvecm_corosync_addresses[Link Address Types]).
648
649 In this example, we want to switch cluster communication to the
650 10.10.10.1/25 network, so we change the 'ring0_addr' of each node respectively.
651
652 NOTE: The exact same procedure can be used to change other 'ringX_addr' values
653 as well. However, we recommend only changing one link address at a time, so
654 that it's easier to recover if something goes wrong.
655
656 After we increase the 'config_version' property, the new configuration file
657 should look like:
658
659 ----
660 logging {
661 debug: off
662 to_syslog: yes
663 }
664
665 nodelist {
666
667 node {
668 name: due
669 nodeid: 2
670 quorum_votes: 1
671 ring0_addr: 10.10.10.2
672 }
673
674 node {
675 name: tre
676 nodeid: 3
677 quorum_votes: 1
678 ring0_addr: 10.10.10.3
679 }
680
681 node {
682 name: uno
683 nodeid: 1
684 quorum_votes: 1
685 ring0_addr: 10.10.10.1
686 }
687
688 }
689
690 quorum {
691 provider: corosync_votequorum
692 }
693
694 totem {
695 cluster_name: testcluster
696 config_version: 4
697 ip_version: ipv4-6
698 secauth: on
699 version: 2
700 interface {
701 linknumber: 0
702 }
703
704 }
705 ----
706
707 Then, after a final check to see that all changed information is correct, we
708 save it and once again follow the
709 xref:pvecm_edit_corosync_conf[edit corosync.conf file] section to bring it into
710 effect.
711
712 The changes will be applied live, so restarting corosync is not strictly
713 necessary. If you changed other settings as well, or notice corosync
714 complaining, you can optionally trigger a restart.
715
716 On a single node execute:
717
718 [source,bash]
719 ----
720 systemctl restart corosync
721 ----
722
723 Now check if everything is okay:
724
725 [source,bash]
726 ----
727 systemctl status corosync
728 ----
729
730 If corosync begins to work again, restart it on all other nodes too.
731 They will then join the cluster membership one by one on the new network.
732
733 [[pvecm_corosync_addresses]]
734 Corosync Addresses
735 ~~~~~~~~~~~~~~~~~~
736
737 A corosync link address (for backwards compatibility denoted by 'ringX_addr' in
738 `corosync.conf`) can be specified in two ways:
739
740 * **IPv4/v6 addresses** can be used directly. They are recommended, since they
741 are static and usually not changed carelessly.
742
743 * **Hostnames** will be resolved using `getaddrinfo`, which means that by
744 default, IPv6 addresses will be used first, if available (see also
745 `man gai.conf`). Keep this in mind, especially when upgrading an existing
746 cluster to IPv6.
747
748 CAUTION: Hostnames should be used with care, since the addresses they
749 resolve to can be changed without touching corosync or the node it runs on -
750 which may lead to a situation where an address is changed without thinking
751 about implications for corosync.
752
753 A separate, static hostname specifically for corosync is recommended, if
754 hostnames are preferred. Also, make sure that every node in the cluster can
755 resolve all hostnames correctly.
756
757 Since {pve} 5.1, while supported, hostnames will be resolved at the time of
758 entry. Only the resolved IP is saved to the configuration.
759
760 Nodes that joined the cluster on earlier versions likely still use their
761 unresolved hostname in `corosync.conf`. It might be a good idea to replace
762 them with IPs or a separate hostname, as mentioned above.
763
764
765 [[pvecm_redundancy]]
766 Corosync Redundancy
767 -------------------
768
769 Corosync supports redundant networking via its integrated Kronosnet layer by
770 default (it is not supported on the legacy udp/udpu transports). It can be
771 enabled by specifying more than one link address, either via the '--linkX'
772 parameters of `pvecm`, in the GUI as **Link 1** (while creating a cluster or
773 adding a new node) or by specifying more than one 'ringX_addr' in
774 `corosync.conf`.
775
776 NOTE: To provide useful failover, every link should be on its own
777 physical network connection.
778
779 Links are used according to a priority setting. You can configure this priority
780 by setting 'knet_link_priority' in the corresponding interface section in
781 `corosync.conf`, or, preferably, using the 'priority' parameter when creating
782 your cluster with `pvecm`:
783
784 ----
785 # pvecm create CLUSTERNAME --link0 10.10.10.1,priority=15 --link1 10.20.20.1,priority=20
786 ----
787
788 This would cause 'link1' to be used first, since it has the higher priority.
789
790 If no priorities are configured manually (or two links have the same priority),
791 links will be used in order of their number, with the lower number having higher
792 priority.
793
794 Even if all links are working, only the one with the highest priority will see
795 corosync traffic. Link priorities cannot be mixed, meaning that links with
796 different priorities will not be able to communicate with each other.
797
798 Since lower priority links will not see traffic unless all higher priorities
799 have failed, it becomes a useful strategy to specify networks used for
800 other tasks (VMs, storage, etc.) as low-priority links. If worst comes to
801 worst, a higher latency or more congested connection might be better than no
802 connection at all.
803
804 Adding Redundant Links To An Existing Cluster
805 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
806
807 To add a new link to a running configuration, first check how to
808 xref:pvecm_edit_corosync_conf[edit the corosync.conf file].
809
810 Then, add a new 'ringX_addr' to every node in the `nodelist` section. Make
811 sure that your 'X' is the same for every node you add it to, and that it is
812 unique for each node.
813
814 Lastly, add a new 'interface', as shown below, to your `totem`
815 section, replacing 'X' with the link number chosen above.
816
817 Assuming you added a link with number 1, the new configuration file could look
818 like this:
819
820 ----
821 logging {
822 debug: off
823 to_syslog: yes
824 }
825
826 nodelist {
827
828 node {
829 name: due
830 nodeid: 2
831 quorum_votes: 1
832 ring0_addr: 10.10.10.2
833 ring1_addr: 10.20.20.2
834 }
835
836 node {
837 name: tre
838 nodeid: 3
839 quorum_votes: 1
840 ring0_addr: 10.10.10.3
841 ring1_addr: 10.20.20.3
842 }
843
844 node {
845 name: uno
846 nodeid: 1
847 quorum_votes: 1
848 ring0_addr: 10.10.10.1
849 ring1_addr: 10.20.20.1
850 }
851
852 }
853
854 quorum {
855 provider: corosync_votequorum
856 }
857
858 totem {
859 cluster_name: testcluster
860 config_version: 4
861 ip_version: ipv4-6
862 secauth: on
863 version: 2
864 interface {
865 linknumber: 0
866 }
867 interface {
868 linknumber: 1
869 }
870 }
871 ----
872
873 The new link will be enabled as soon as you follow the last steps to
874 xref:pvecm_edit_corosync_conf[edit the corosync.conf file]. A restart should not
875 be necessary. You can check that corosync loaded the new link using:
876
877 ----
878 journalctl -b -u corosync
879 ----
880
881 It might be a good idea to test the new link by temporarily disconnecting the
882 old link on one node and making sure that its status remains online while
883 disconnected:
884
885 ----
886 pvecm status
887 ----
888
889 If you see a healthy cluster state, it means that your new link is being used.
890
891
892 Role of SSH in {pve} Clusters
893 -----------------------------
894
895 {pve} utilizes SSH tunnels for various features.
896
897 * Proxying console/shell sessions (node and guests)
898 +
899 When using the shell for node B while being connected to node A, connects to a
900 terminal proxy on node A, which is in turn connected to the login shell on node
901 B via a non-interactive SSH tunnel.
902
903 * VM and CT memory and local-storage migration in 'secure' mode.
904 +
905 During the migration, one or more SSH tunnel(s) are established between the
906 source and target nodes, in order to exchange migration information and
907 transfer memory and disk contents.
908
909 * Storage replication
910
911 .Pitfalls due to automatic execution of `.bashrc` and siblings
912 [IMPORTANT]
913 ====
914 In case you have a custom `.bashrc`, or similar files that get executed on
915 login by the configured shell, `ssh` will automatically run it once the session
916 is established successfully. This can cause some unexpected behavior, as those
917 commands may be executed with root permissions on any of the operations
918 described above. This can cause possible problematic side-effects!
919
920 In order to avoid such complications, it's recommended to add a check in
921 `/root/.bashrc` to make sure the session is interactive, and only then run
922 `.bashrc` commands.
923
924 You can add this snippet at the beginning of your `.bashrc` file:
925
926 ----
927 # Early exit if not running interactively to avoid side-effects!
928 case $- in
929 *i*) ;;
930 *) return;;
931 esac
932 ----
933 ====
934
935
936 Corosync External Vote Support
937 ------------------------------
938
939 This section describes a way to deploy an external voter in a {pve} cluster.
940 When configured, the cluster can sustain more node failures without
941 violating safety properties of the cluster communication.
942
943 For this to work, there are two services involved:
944
945 * A QDevice daemon which runs on each {pve} node
946
947 * An external vote daemon which runs on an independent server
948
949 As a result, you can achieve higher availability, even in smaller setups (for
950 example 2+1 nodes).
951
952 QDevice Technical Overview
953 ~~~~~~~~~~~~~~~~~~~~~~~~~~
954
955 The Corosync Quorum Device (QDevice) is a daemon which runs on each cluster
956 node. It provides a configured number of votes to the cluster's quorum
957 subsystem, based on an externally running third-party arbitrator's decision.
958 Its primary use is to allow a cluster to sustain more node failures than
959 standard quorum rules allow. This can be done safely as the external device
960 can see all nodes and thus choose only one set of nodes to give its vote.
961 This will only be done if said set of nodes can have quorum (again) after
962 receiving the third-party vote.
963
964 Currently, only 'QDevice Net' is supported as a third-party arbitrator. This is
965 a daemon which provides a vote to a cluster partition, if it can reach the
966 partition members over the network. It will only give votes to one partition
967 of a cluster at any time.
968 It's designed to support multiple clusters and is almost configuration and
969 state free. New clusters are handled dynamically and no configuration file
970 is needed on the host running a QDevice.
971
972 The only requirements for the external host are that it needs network access to
973 the cluster and to have a corosync-qnetd package available. We provide a package
974 for Debian based hosts, and other Linux distributions should also have a package
975 available through their respective package manager.
976
977 NOTE: In contrast to corosync itself, a QDevice connects to the cluster over
978 TCP/IP. The daemon may even run outside of the cluster's LAN and can have longer
979 latencies than 2 ms.
980
981 Supported Setups
982 ~~~~~~~~~~~~~~~~
983
984 We support QDevices for clusters with an even number of nodes and recommend
985 it for 2 node clusters, if they should provide higher availability.
986 For clusters with an odd node count, we currently discourage the use of
987 QDevices. The reason for this is the difference in the votes which the QDevice
988 provides for each cluster type. Even numbered clusters get a single additional
989 vote, which only increases availability, because if the QDevice
990 itself fails, you are in the same position as with no QDevice at all.
991
992 On the other hand, with an odd numbered cluster size, the QDevice provides
993 '(N-1)' votes -- where 'N' corresponds to the cluster node count. This
994 alternative behavior makes sense; if it had only one additional vote, the
995 cluster could get into a split-brain situation. This algorithm allows for all
996 nodes but one (and naturally the QDevice itself) to fail. However, there are two
997 drawbacks to this:
998
999 * If the QNet daemon itself fails, no other node may fail or the cluster
1000 immediately loses quorum. For example, in a cluster with 15 nodes, 7
1001 could fail before the cluster becomes inquorate. But, if a QDevice is
1002 configured here and it itself fails, **no single node** of the 15 may fail.
1003 The QDevice acts almost as a single point of failure in this case.
1004
1005 * The fact that all but one node plus QDevice may fail sounds promising at
1006 first, but this may result in a mass recovery of HA services, which could
1007 overload the single remaining node. Furthermore, a Ceph server will stop
1008 providing services if only '((N-1)/2)' nodes or less remain online.
1009
1010 If you understand the drawbacks and implications, you can decide yourself if
1011 you want to use this technology in an odd numbered cluster setup.
1012
1013 QDevice-Net Setup
1014 ~~~~~~~~~~~~~~~~~
1015
1016 We recommend running any daemon which provides votes to corosync-qdevice as an
1017 unprivileged user. {pve} and Debian provide a package which is already
1018 configured to do so.
1019 The traffic between the daemon and the cluster must be encrypted to ensure a
1020 safe and secure integration of the QDevice in {pve}.
1021
1022 First, install the 'corosync-qnetd' package on your external server
1023
1024 ----
1025 external# apt install corosync-qnetd
1026 ----
1027
1028 and the 'corosync-qdevice' package on all cluster nodes
1029
1030 ----
1031 pve# apt install corosync-qdevice
1032 ----
1033
1034 After doing this, ensure that all the nodes in the cluster are online.
1035
1036 You can now set up your QDevice by running the following command on one
1037 of the {pve} nodes:
1038
1039 ----
1040 pve# pvecm qdevice setup <QDEVICE-IP>
1041 ----
1042
1043 The SSH key from the cluster will be automatically copied to the QDevice.
1044
1045 NOTE: Make sure that the SSH configuration on your external server allows root
1046 login via password, if you are asked for a password during this step.
1047
1048 After you enter the password and all the steps have successfully completed, you
1049 will see "Done". You can verify that the QDevice has been set up with:
1050
1051 ----
1052 pve# pvecm status
1053
1054 ...
1055
1056 Votequorum information
1057 ~~~~~~~~~~~~~~~~~~~~~
1058 Expected votes: 3
1059 Highest expected: 3
1060 Total votes: 3
1061 Quorum: 2
1062 Flags: Quorate Qdevice
1063
1064 Membership information
1065 ~~~~~~~~~~~~~~~~~~~~~~
1066 Nodeid Votes Qdevice Name
1067 0x00000001 1 A,V,NMW 192.168.22.180 (local)
1068 0x00000002 1 A,V,NMW 192.168.22.181
1069 0x00000000 1 Qdevice
1070
1071 ----
1072
1073
1074 Frequently Asked Questions
1075 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1076
1077 Tie Breaking
1078 ^^^^^^^^^^^^
1079
1080 In case of a tie, where two same-sized cluster partitions cannot see each other
1081 but can see the QDevice, the QDevice chooses one of those partitions randomly
1082 and provides a vote to it.
1083
1084 Possible Negative Implications
1085 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1086
1087 For clusters with an even node count, there are no negative implications when
1088 using a QDevice. If it fails to work, it is the same as not having a QDevice
1089 at all.
1090
1091 Adding/Deleting Nodes After QDevice Setup
1092 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1093
1094 If you want to add a new node or remove an existing one from a cluster with a
1095 QDevice setup, you need to remove the QDevice first. After that, you can add or
1096 remove nodes normally. Once you have a cluster with an even node count again,
1097 you can set up the QDevice again as described previously.
1098
1099 Removing the QDevice
1100 ^^^^^^^^^^^^^^^^^^^^
1101
1102 If you used the official `pvecm` tool to add the QDevice, you can remove it
1103 by running:
1104
1105 ----
1106 pve# pvecm qdevice remove
1107 ----
1108
1109 //Still TODO
1110 //^^^^^^^^^^
1111 //There is still stuff to add here
1112
1113
1114 Corosync Configuration
1115 ----------------------
1116
1117 The `/etc/pve/corosync.conf` file plays a central role in a {pve} cluster. It
1118 controls the cluster membership and its network.
1119 For further information about it, check the corosync.conf man page:
1120 [source,bash]
1121 ----
1122 man corosync.conf
1123 ----
1124
1125 For node membership, you should always use the `pvecm` tool provided by {pve}.
1126 You may have to edit the configuration file manually for other changes.
1127 Here are a few best practice tips for doing this.
1128
1129 [[pvecm_edit_corosync_conf]]
1130 Edit corosync.conf
1131 ~~~~~~~~~~~~~~~~~~
1132
1133 Editing the corosync.conf file is not always very straightforward. There are
1134 two on each cluster node, one in `/etc/pve/corosync.conf` and the other in
1135 `/etc/corosync/corosync.conf`. Editing the one in our cluster file system will
1136 propagate the changes to the local one, but not vice versa.
1137
1138 The configuration will get updated automatically, as soon as the file changes.
1139 This means that changes which can be integrated in a running corosync will take
1140 effect immediately. Thus, you should always make a copy and edit that instead,
1141 to avoid triggering unintended changes when saving the file while editing.
1142
1143 [source,bash]
1144 ----
1145 cp /etc/pve/corosync.conf /etc/pve/corosync.conf.new
1146 ----
1147
1148 Then, open the config file with your favorite editor, such as `nano` or
1149 `vim.tiny`, which come pre-installed on every {pve} node.
1150
1151 NOTE: Always increment the 'config_version' number after configuration changes;
1152 omitting this can lead to problems.
1153
1154 After making the necessary changes, create another copy of the current working
1155 configuration file. This serves as a backup if the new configuration fails to
1156 apply or causes other issues.
1157
1158 [source,bash]
1159 ----
1160 cp /etc/pve/corosync.conf /etc/pve/corosync.conf.bak
1161 ----
1162
1163 Then replace the old configuration file with the new one:
1164 [source,bash]
1165 ----
1166 mv /etc/pve/corosync.conf.new /etc/pve/corosync.conf
1167 ----
1168
1169 You can check if the changes could be applied automatically, using the following
1170 commands:
1171 [source,bash]
1172 ----
1173 systemctl status corosync
1174 journalctl -b -u corosync
1175 ----
1176
1177 If the changes could not be applied automatically, you may have to restart the
1178 corosync service via:
1179 [source,bash]
1180 ----
1181 systemctl restart corosync
1182 ----
1183
1184 On errors, check the troubleshooting section below.
1185
1186 Troubleshooting
1187 ~~~~~~~~~~~~~~~
1188
1189 Issue: 'quorum.expected_votes must be configured'
1190 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1191
1192 When corosync starts to fail and you get the following message in the system log:
1193
1194 ----
1195 [...]
1196 corosync[1647]: [QUORUM] Quorum provider: corosync_votequorum failed to initialize.
1197 corosync[1647]: [SERV ] Service engine 'corosync_quorum' failed to load for reason
1198 'configuration error: nodelist or quorum.expected_votes must be configured!'
1199 [...]
1200 ----
1201
1202 It means that the hostname you set for a corosync 'ringX_addr' in the
1203 configuration could not be resolved.
1204
1205 Write Configuration When Not Quorate
1206 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1207
1208 If you need to change '/etc/pve/corosync.conf' on a node with no quorum, and you
1209 understand what you are doing, use:
1210 [source,bash]
1211 ----
1212 pvecm expected 1
1213 ----
1214
1215 This sets the expected vote count to 1 and makes the cluster quorate. You can
1216 then fix your configuration, or revert it back to the last working backup.
1217
1218 This is not enough if corosync cannot start anymore. In that case, it is best to
1219 edit the local copy of the corosync configuration in
1220 '/etc/corosync/corosync.conf', so that corosync can start again. Ensure that on
1221 all nodes, this configuration has the same content to avoid split-brain
1222 situations.
1223
1224
1225 [[pvecm_corosync_conf_glossary]]
1226 Corosync Configuration Glossary
1227 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1228
1229 ringX_addr::
1230 This names the different link addresses for the Kronosnet connections between
1231 nodes.
1232
1233
1234 Cluster Cold Start
1235 ------------------
1236
1237 It is obvious that a cluster is not quorate when all nodes are
1238 offline. This is a common case after a power failure.
1239
1240 NOTE: It is always a good idea to use an uninterruptible power supply
1241 (``UPS'', also called ``battery backup'') to avoid this state, especially if
1242 you want HA.
1243
1244 On node startup, the `pve-guests` service is started and waits for
1245 quorum. Once quorate, it starts all guests which have the `onboot`
1246 flag set.
1247
1248 When you turn on nodes, or when power comes back after power failure,
1249 it is likely that some nodes will boot faster than others. Please keep in
1250 mind that guest startup is delayed until you reach quorum.
1251
1252
1253 Guest Migration
1254 ---------------
1255
1256 Migrating virtual guests to other nodes is a useful feature in a
1257 cluster. There are settings to control the behavior of such
1258 migrations. This can be done via the configuration file
1259 `datacenter.cfg` or for a specific migration via API or command line
1260 parameters.
1261
1262 It makes a difference if a guest is online or offline, or if it has
1263 local resources (like a local disk).
1264
1265 For details about virtual machine migration, see the
1266 xref:qm_migration[QEMU/KVM Migration Chapter].
1267
1268 For details about container migration, see the
1269 xref:pct_migration[Container Migration Chapter].
1270
1271 Migration Type
1272 ~~~~~~~~~~~~~~
1273
1274 The migration type defines if the migration data should be sent over an
1275 encrypted (`secure`) channel or an unencrypted (`insecure`) one.
1276 Setting the migration type to insecure means that the RAM content of a
1277 virtual guest is also transferred unencrypted, which can lead to
1278 information disclosure of critical data from inside the guest (for
1279 example, passwords or encryption keys).
1280
1281 Therefore, we strongly recommend using the secure channel if you do
1282 not have full control over the network and can not guarantee that no
1283 one is eavesdropping on it.
1284
1285 NOTE: Storage migration does not follow this setting. Currently, it
1286 always sends the storage content over a secure channel.
1287
1288 Encryption requires a lot of computing power, so this setting is often
1289 changed to "unsafe" to achieve better performance. The impact on
1290 modern systems is lower because they implement AES encryption in
1291 hardware. The performance impact is particularly evident in fast
1292 networks, where you can transfer 10 Gbps or more.
1293
1294 Migration Network
1295 ~~~~~~~~~~~~~~~~~
1296
1297 By default, {pve} uses the network in which cluster communication
1298 takes place to send the migration traffic. This is not optimal both because
1299 sensitive cluster traffic can be disrupted and this network may not
1300 have the best bandwidth available on the node.
1301
1302 Setting the migration network parameter allows the use of a dedicated
1303 network for all migration traffic. In addition to the memory,
1304 this also affects the storage traffic for offline migrations.
1305
1306 The migration network is set as a network using CIDR notation. This
1307 has the advantage that you don't have to set individual IP addresses
1308 for each node. {pve} can determine the real address on the
1309 destination node from the network specified in the CIDR form. To
1310 enable this, the network must be specified so that each node has exactly one
1311 IP in the respective network.
1312
1313 Example
1314 ^^^^^^^
1315
1316 We assume that we have a three-node setup, with three separate
1317 networks. One for public communication with the Internet, one for
1318 cluster communication, and a very fast one, which we want to use as a
1319 dedicated network for migration.
1320
1321 A network configuration for such a setup might look as follows:
1322
1323 ----
1324 iface eno1 inet manual
1325
1326 # public network
1327 auto vmbr0
1328 iface vmbr0 inet static
1329 address 192.X.Y.57/24
1330 gateway 192.X.Y.1
1331 bridge-ports eno1
1332 bridge-stp off
1333 bridge-fd 0
1334
1335 # cluster network
1336 auto eno2
1337 iface eno2 inet static
1338 address 10.1.1.1/24
1339
1340 # fast network
1341 auto eno3
1342 iface eno3 inet static
1343 address 10.1.2.1/24
1344 ----
1345
1346 Here, we will use the network 10.1.2.0/24 as a migration network. For
1347 a single migration, you can do this using the `migration_network`
1348 parameter of the command line tool:
1349
1350 ----
1351 # qm migrate 106 tre --online --migration_network 10.1.2.0/24
1352 ----
1353
1354 To configure this as the default network for all migrations in the
1355 cluster, set the `migration` property of the `/etc/pve/datacenter.cfg`
1356 file:
1357
1358 ----
1359 # use dedicated migration network
1360 migration: secure,network=10.1.2.0/24
1361 ----
1362
1363 NOTE: The migration type must always be set when the migration network
1364 is set in `/etc/pve/datacenter.cfg`.
1365
1366
1367 ifdef::manvolnum[]
1368 include::pve-copyright.adoc[]
1369 endif::manvolnum[]