]>
Commit | Line | Data |
---|---|---|
1 | [[chapter_ha_manager]] | |
2 | ifdef::manvolnum[] | |
3 | ha-manager(1) | |
4 | ============= | |
5 | :pve-toplevel: | |
6 | ||
7 | NAME | |
8 | ---- | |
9 | ||
10 | ha-manager - Proxmox VE HA Manager | |
11 | ||
12 | SYNOPSIS | |
13 | -------- | |
14 | ||
15 | include::ha-manager.1-synopsis.adoc[] | |
16 | ||
17 | DESCRIPTION | |
18 | ----------- | |
19 | endif::manvolnum[] | |
20 | ifndef::manvolnum[] | |
21 | High Availability | |
22 | ================= | |
23 | :pve-toplevel: | |
24 | endif::manvolnum[] | |
25 | ||
26 | Our modern society depends heavily on information provided by | |
27 | computers over the network. Mobile devices amplified that dependency, | |
28 | because people can access the network any time from anywhere. If you | |
29 | provide such services, it is very important that they are available | |
30 | most of the time. | |
31 | ||
32 | We can mathematically define the availability as the ratio of (A) the | |
33 | total time a service is capable of being used during a given interval | |
34 | to (B) the length of the interval. It is normally expressed as a | |
35 | percentage of uptime in a given year. | |
36 | ||
37 | .Availability - Downtime per Year | |
38 | [width="60%",cols="<d,d",options="header"] | |
39 | |=========================================================== | |
40 | |Availability % |Downtime per year | |
41 | |99 |3.65 days | |
42 | |99.9 |8.76 hours | |
43 | |99.99 |52.56 minutes | |
44 | |99.999 |5.26 minutes | |
45 | |99.9999 |31.5 seconds | |
46 | |99.99999 |3.15 seconds | |
47 | |=========================================================== | |
48 | ||
49 | There are several ways to increase availability. The most elegant | |
50 | solution is to rewrite your software, so that you can run it on | |
51 | several host at the same time. The software itself need to have a way | |
52 | to detect errors and do failover. This is relatively easy if you just | |
53 | want to serve read-only web pages. But in general this is complex, and | |
54 | sometimes impossible because you cannot modify the software | |
55 | yourself. The following solutions works without modifying the | |
56 | software: | |
57 | ||
58 | * Use reliable ``server'' components | |
59 | + | |
60 | NOTE: Computer components with same functionality can have varying | |
61 | reliability numbers, depending on the component quality. Most vendors | |
62 | sell components with higher reliability as ``server'' components - | |
63 | usually at higher price. | |
64 | ||
65 | * Eliminate single point of failure (redundant components) | |
66 | ** use an uninterruptible power supply (UPS) | |
67 | ** use redundant power supplies on the main boards | |
68 | ** use ECC-RAM | |
69 | ** use redundant network hardware | |
70 | ** use RAID for local storage | |
71 | ** use distributed, redundant storage for VM data | |
72 | ||
73 | * Reduce downtime | |
74 | ** rapidly accessible administrators (24/7) | |
75 | ** availability of spare parts (other nodes in a {pve} cluster) | |
76 | ** automatic error detection (provided by `ha-manager`) | |
77 | ** automatic failover (provided by `ha-manager`) | |
78 | ||
79 | Virtualization environments like {pve} make it much easier to reach | |
80 | high availability because they remove the ``hardware'' dependency. They | |
81 | also support to setup and use redundant storage and network | |
82 | devices. So if one host fail, you can simply start those services on | |
83 | another host within your cluster. | |
84 | ||
85 | Even better, {pve} provides a software stack called `ha-manager`, | |
86 | which can do that automatically for you. It is able to automatically | |
87 | detect errors and do automatic failover. | |
88 | ||
89 | {pve} `ha-manager` works like an ``automated'' administrator. First, you | |
90 | configure what resources (VMs, containers, ...) it should | |
91 | manage. `ha-manager` then observes correct functionality, and handles | |
92 | service failover to another node in case of errors. `ha-manager` can | |
93 | also handle normal user requests which may start, stop, relocate and | |
94 | migrate a service. | |
95 | ||
96 | But high availability comes at a price. High quality components are | |
97 | more expensive, and making them redundant duplicates the costs at | |
98 | least. Additional spare parts increase costs further. So you should | |
99 | carefully calculate the benefits, and compare with those additional | |
100 | costs. | |
101 | ||
102 | TIP: Increasing availability from 99% to 99.9% is relatively | |
103 | simply. But increasing availability from 99.9999% to 99.99999% is very | |
104 | hard and costly. `ha-manager` has typical error detection and failover | |
105 | times of about 2 minutes, so you can get no more than 99.999% | |
106 | availability. | |
107 | ||
108 | ||
109 | Requirements | |
110 | ------------ | |
111 | ||
112 | You must meet the following requirements before you start with HA: | |
113 | ||
114 | * at least three cluster nodes (to get reliable quorum) | |
115 | ||
116 | * shared storage for VMs and containers | |
117 | ||
118 | * hardware redundancy (everywhere) | |
119 | ||
120 | * use reliable “server” components | |
121 | ||
122 | * hardware watchdog - if not available we fall back to the | |
123 | linux kernel software watchdog (`softdog`) | |
124 | ||
125 | * optional hardware fencing devices | |
126 | ||
127 | ||
128 | [[ha_manager_resources]] | |
129 | Resources | |
130 | --------- | |
131 | ||
132 | We call the primary management unit handled by `ha-manager` a | |
133 | resource. A resource (also called ``service'') is uniquely | |
134 | identified by a service ID (SID), which consists of the resource type | |
135 | and an type specific ID, e.g.: `vm:100`. That example would be a | |
136 | resource of type `vm` (virtual machine) with the ID 100. | |
137 | ||
138 | For now we have two important resources types - virtual machines and | |
139 | containers. One basic idea here is that we can bundle related software | |
140 | into such VM or container, so there is no need to compose one big | |
141 | service from other services, like it was done with `rgmanager`. In | |
142 | general, a HA enabled resource should not depend on other resources. | |
143 | ||
144 | ||
145 | How It Works | |
146 | ------------ | |
147 | ||
148 | This section provides a detailed description of the {PVE} HA manager | |
149 | internals. It describes all involved daemons and how they work | |
150 | together. To provide HA, two daemons run on each node: | |
151 | ||
152 | `pve-ha-lrm`:: | |
153 | ||
154 | The local resource manager (LRM), which controls the services running on | |
155 | the local node. It reads the requested states for its services from | |
156 | the current manager status file and executes the respective commands. | |
157 | ||
158 | `pve-ha-crm`:: | |
159 | ||
160 | The cluster resource manager (CRM), which makes the cluster wide | |
161 | decisions. It sends commands to the LRM, processes the results, | |
162 | and moves resources to other nodes if something fails. The CRM also | |
163 | handles node fencing. | |
164 | ||
165 | ||
166 | .Locks in the LRM & CRM | |
167 | [NOTE] | |
168 | Locks are provided by our distributed configuration file system (pmxcfs). | |
169 | They are used to guarantee that each LRM is active once and working. As a | |
170 | LRM only executes actions when it holds its lock we can mark a failed node | |
171 | as fenced if we can acquire its lock. This lets us then recover any failed | |
172 | HA services securely without any interference from the now unknown failed node. | |
173 | This all gets supervised by the CRM which holds currently the manager master | |
174 | lock. | |
175 | ||
176 | ||
177 | Service States | |
178 | ~~~~~~~~~~~~~~ | |
179 | ||
180 | [thumbnail="gui-ha-manager-status.png"] | |
181 | ||
182 | The CRM use a service state enumeration to record the current service | |
183 | state. We display this state on the GUI and you can query it using | |
184 | the `ha-manager` command line tool: | |
185 | ||
186 | ---- | |
187 | # ha-manager status | |
188 | quorum OK | |
189 | master elsa (active, Mon Nov 21 07:23:29 2016) | |
190 | lrm elsa (active, Mon Nov 21 07:23:22 2016) | |
191 | service ct:100 (elsa, stopped) | |
192 | service ct:102 (elsa, started) | |
193 | service vm:501 (elsa, started) | |
194 | ---- | |
195 | ||
196 | Here is the list of possible states: | |
197 | ||
198 | stopped:: | |
199 | ||
200 | Service is stopped (confirmed by LRM). If the LRM detects a stopped | |
201 | service is still running, it will stop it again. | |
202 | ||
203 | request_stop:: | |
204 | ||
205 | Service should be stopped. The CRM waits for confirmation from the | |
206 | LRM. | |
207 | ||
208 | started:: | |
209 | ||
210 | Service is active an LRM should start it ASAP if not already running. | |
211 | If the Service fails and is detected to be not running the LRM | |
212 | restarts it | |
213 | (see xref:ha_manager_start_failure_policy[Start Failure Policy]). | |
214 | ||
215 | fence:: | |
216 | ||
217 | Wait for node fencing (service node is not inside quorate cluster | |
218 | partition). As soon as node gets fenced successfully the service will | |
219 | be recovered to another node, if possible | |
220 | (see xref:ha_manager_fencing[Fencing]). | |
221 | ||
222 | freeze:: | |
223 | ||
224 | Do not touch the service state. We use this state while we reboot a | |
225 | node, or when we restart the LRM daemon | |
226 | (see xref:ha_manager_package_updates[Package Updates]). | |
227 | ||
228 | migrate:: | |
229 | ||
230 | Migrate service (live) to other node. | |
231 | ||
232 | error:: | |
233 | ||
234 | Service is disabled because of LRM errors. Needs manual intervention | |
235 | (see xref:ha_manager_error_recovery[Error Recovery]). | |
236 | ||
237 | ||
238 | Local Resource Manager | |
239 | ~~~~~~~~~~~~~~~~~~~~~~ | |
240 | ||
241 | The local resource manager (`pve-ha-lrm`) is started as a daemon on | |
242 | boot and waits until the HA cluster is quorate and thus cluster wide | |
243 | locks are working. | |
244 | ||
245 | It can be in three states: | |
246 | ||
247 | wait for agent lock:: | |
248 | ||
249 | The LRM waits for our exclusive lock. This is also used as idle state if no | |
250 | service is configured. | |
251 | ||
252 | active:: | |
253 | ||
254 | The LRM holds its exclusive lock and has services configured. | |
255 | ||
256 | lost agent lock:: | |
257 | ||
258 | The LRM lost its lock, this means a failure happened and quorum was lost. | |
259 | ||
260 | After the LRM gets in the active state it reads the manager status | |
261 | file in `/etc/pve/ha/manager_status` and determines the commands it | |
262 | has to execute for the services it owns. | |
263 | For each command a worker gets started, this workers are running in | |
264 | parallel and are limited to at most 4 by default. This default setting | |
265 | may be changed through the datacenter configuration key `max_worker`. | |
266 | When finished the worker process gets collected and its result saved for | |
267 | the CRM. | |
268 | ||
269 | .Maximum Concurrent Worker Adjustment Tips | |
270 | [NOTE] | |
271 | The default value of at most 4 concurrent workers may be unsuited for | |
272 | a specific setup. For example may 4 live migrations happen at the same | |
273 | time, which can lead to network congestions with slower networks and/or | |
274 | big (memory wise) services. Ensure that also in the worst case no congestion | |
275 | happens and lower the `max_worker` value if needed. In the contrary, if you | |
276 | have a particularly powerful high end setup you may also want to increase it. | |
277 | ||
278 | Each command requested by the CRM is uniquely identifiable by an UID, when | |
279 | the worker finished its result will be processed and written in the LRM | |
280 | status file `/etc/pve/nodes/<nodename>/lrm_status`. There the CRM may collect | |
281 | it and let its state machine - respective the commands output - act on it. | |
282 | ||
283 | The actions on each service between CRM and LRM are normally always synced. | |
284 | This means that the CRM requests a state uniquely marked by an UID, the LRM | |
285 | then executes this action *one time* and writes back the result, also | |
286 | identifiable by the same UID. This is needed so that the LRM does not | |
287 | executes an outdated command. | |
288 | With the exception of the `stop` and the `error` command, | |
289 | those two do not depend on the result produced and are executed | |
290 | always in the case of the stopped state and once in the case of | |
291 | the error state. | |
292 | ||
293 | .Read the Logs | |
294 | [NOTE] | |
295 | The HA Stack logs every action it makes. This helps to understand what | |
296 | and also why something happens in the cluster. Here its important to see | |
297 | what both daemons, the LRM and the CRM, did. You may use | |
298 | `journalctl -u pve-ha-lrm` on the node(s) where the service is and | |
299 | the same command for the pve-ha-crm on the node which is the current master. | |
300 | ||
301 | Cluster Resource Manager | |
302 | ~~~~~~~~~~~~~~~~~~~~~~~~ | |
303 | ||
304 | The cluster resource manager (`pve-ha-crm`) starts on each node and | |
305 | waits there for the manager lock, which can only be held by one node | |
306 | at a time. The node which successfully acquires the manager lock gets | |
307 | promoted to the CRM master. | |
308 | ||
309 | It can be in three states: | |
310 | ||
311 | wait for agent lock:: | |
312 | ||
313 | The CRM waits for our exclusive lock. This is also used as idle state if no | |
314 | service is configured | |
315 | ||
316 | active:: | |
317 | ||
318 | The CRM holds its exclusive lock and has services configured | |
319 | ||
320 | lost agent lock:: | |
321 | ||
322 | The CRM lost its lock, this means a failure happened and quorum was lost. | |
323 | ||
324 | It main task is to manage the services which are configured to be highly | |
325 | available and try to always enforce them to the wanted state, e.g.: a | |
326 | enabled service will be started if its not running, if it crashes it will | |
327 | be started again. Thus it dictates the LRM the actions it needs to execute. | |
328 | ||
329 | When an node leaves the cluster quorum, its state changes to unknown. | |
330 | If the current CRM then can secure the failed nodes lock, the services | |
331 | will be 'stolen' and restarted on another node. | |
332 | ||
333 | When a cluster member determines that it is no longer in the cluster | |
334 | quorum, the LRM waits for a new quorum to form. As long as there is no | |
335 | quorum the node cannot reset the watchdog. This will trigger a reboot | |
336 | after the watchdog then times out, this happens after 60 seconds. | |
337 | ||
338 | ||
339 | Configuration | |
340 | ------------- | |
341 | ||
342 | The HA stack is well integrated into the {pve} API. So, for example, | |
343 | HA can be configured via the `ha-manager` command line interface, or | |
344 | the {pve} web interface - both interfaces provide an easy way to | |
345 | manage HA. Automation tools can use the API directly. | |
346 | ||
347 | All HA configuration files are within `/etc/pve/ha/`, so they get | |
348 | automatically distributed to the cluster nodes, and all nodes share | |
349 | the same HA configuration. | |
350 | ||
351 | ||
352 | Resources | |
353 | ~~~~~~~~~ | |
354 | ||
355 | [thumbnail="gui-ha-manager-resources-view.png"] | |
356 | ||
357 | The resource configuration file `/etc/pve/ha/resources.cfg` stores | |
358 | the list of resources managed by `ha-manager`. A resource configuration | |
359 | inside that list look like this: | |
360 | ||
361 | ---- | |
362 | <type>: <name> | |
363 | <property> <value> | |
364 | ... | |
365 | ---- | |
366 | ||
367 | It starts with a resource type followed by a resource specific name, | |
368 | separated with colon. Together this forms the HA resource ID, which is | |
369 | used by all `ha-manager` commands to uniquely identify a resource | |
370 | (example: `vm:100` or `ct:101`). The next lines contain additional | |
371 | properties: | |
372 | ||
373 | include::ha-resources-opts.adoc[] | |
374 | ||
375 | Here is a real world example with one VM and one container. As you see, | |
376 | the syntax of those files is really simple, so it is even posiible to | |
377 | read or edit those files using your favorite editor: | |
378 | ||
379 | .Configuration Example (`/etc/pve/ha/resources.cfg`) | |
380 | ---- | |
381 | vm: 501 | |
382 | state started | |
383 | max_relocate 2 | |
384 | ||
385 | ct: 102 | |
386 | # Note: use default settings for everything | |
387 | ---- | |
388 | ||
389 | [thumbnail="gui-ha-manager-add-resource.png"] | |
390 | ||
391 | Above config was generated using the `ha-manager` command line tool: | |
392 | ||
393 | ---- | |
394 | # ha-manager add vm:501 --state started --max_relocate 2 | |
395 | # ha-manager add ct:102 | |
396 | ---- | |
397 | ||
398 | ||
399 | [[ha_manager_groups]] | |
400 | Groups | |
401 | ~~~~~~ | |
402 | ||
403 | [thumbnail="gui-ha-manager-groups-view.png"] | |
404 | ||
405 | The HA group configuration file `/etc/pve/ha/groups.cfg` is used to | |
406 | define groups of cluster nodes. A resource can be restricted to run | |
407 | only on the members of such group. A group configuration look like | |
408 | this: | |
409 | ||
410 | ---- | |
411 | group: <group> | |
412 | nodes <node_list> | |
413 | <property> <value> | |
414 | ... | |
415 | ---- | |
416 | ||
417 | include::ha-groups-opts.adoc[] | |
418 | ||
419 | [thumbnail="gui-ha-manager-add-group.png"] | |
420 | ||
421 | A commom requirement is that a resource should run on a specific | |
422 | node. Usually the resource is able to run on other nodes, so you can define | |
423 | an unrestricted group with a single member: | |
424 | ||
425 | ---- | |
426 | # ha-manager groupadd prefer_node1 --nodes node1 | |
427 | ---- | |
428 | ||
429 | For bigger clusters, it makes sense to define a more detailed failover | |
430 | behavior. For example, you may want to run a set of services on | |
431 | `node1` if possible. If `node1` is not available, you want to run them | |
432 | equally splitted on `node2` and `node3`. If those nodes also fail the | |
433 | services should run on `node4`. To achieve this you could set the node | |
434 | list to: | |
435 | ||
436 | ---- | |
437 | # ha-manager groupadd mygroup1 -nodes "node1:2,node2:1,node3:1,node4" | |
438 | ---- | |
439 | ||
440 | Another use case is if a resource uses other resources only available | |
441 | on specific nodes, lets say `node1` and `node2`. We need to make sure | |
442 | that HA manager does not use other nodes, so we need to create a | |
443 | restricted group with said nodes: | |
444 | ||
445 | ---- | |
446 | # ha-manager groupadd mygroup2 -nodes "node1,node2" -restricted | |
447 | ---- | |
448 | ||
449 | Above commands created the following group configuration fils: | |
450 | ||
451 | .Configuration Example (`/etc/pve/ha/groups.cfg`) | |
452 | ---- | |
453 | group: prefer_node1 | |
454 | nodes node1 | |
455 | ||
456 | group: mygroup1 | |
457 | nodes node2:1,node4,node1:2,node3:1 | |
458 | ||
459 | group: mygroup2 | |
460 | nodes node2,node1 | |
461 | restricted 1 | |
462 | ---- | |
463 | ||
464 | ||
465 | The `nofailback` options is mostly useful to avoid unwanted resource | |
466 | movements during administartion tasks. For example, if you need to | |
467 | migrate a service to a node which hasn't the highest priority in the | |
468 | group, you need to tell the HA manager to not move this service | |
469 | instantly back by setting the `nofailback` option. | |
470 | ||
471 | Another scenario is when a service was fenced and it got recovered to | |
472 | another node. The admin tries to repair the fenced node and brings it | |
473 | up online again to investigate the failure cause and check if it runs | |
474 | stable again. Setting the `nofailback` flag prevents that the | |
475 | recovered services move straight back to the fenced node. | |
476 | ||
477 | ||
478 | [[ha_manager_fencing]] | |
479 | Fencing | |
480 | ------- | |
481 | ||
482 | On node failures, fencing ensures that the erroneous node is | |
483 | guaranteed to be offline. This is required to make sure that no | |
484 | resource runs twice when it gets recovered on another node. This is a | |
485 | really important task, because without, it would not be possible to | |
486 | recover a resource on another node. | |
487 | ||
488 | If a node would not get fenced, it would be in an unknown state where | |
489 | it may have still access to shared resources. This is really | |
490 | dangerous! Imagine that every network but the storage one broke. Now, | |
491 | while not reachable from the public network, the VM still runs and | |
492 | writes to the shared storage. | |
493 | ||
494 | If we then simply start up this VM on another node, we would get a | |
495 | dangerous race conditions because we write from both nodes. Such | |
496 | condition can destroy all VM data and the whole VM could be rendered | |
497 | unusable. The recovery could also fail if the storage protects from | |
498 | multiple mounts. | |
499 | ||
500 | ||
501 | How {pve} Fences | |
502 | ~~~~~~~~~~~~~~~~ | |
503 | ||
504 | There are different methods to fence a node, for example, fence | |
505 | devices which cut off the power from the node or disable their | |
506 | communication completely. Those are often quite expensive and bring | |
507 | additional critical components into a system, because if they fail you | |
508 | cannot recover any service. | |
509 | ||
510 | We thus wanted to integrate a simpler fencing method, which does not | |
511 | require additional external hardware. This can be done using | |
512 | watchdog timers. | |
513 | ||
514 | .Possible Fencing Methods | |
515 | - external power switches | |
516 | - isolate nodes by disabling complete network traffic on the switch | |
517 | - self fencing using watchdog timers | |
518 | ||
519 | Watchdog timers are widely used in critical and dependable systems | |
520 | since the beginning of micro controllers. They are often independent | |
521 | and simple integrated circuits which are used to detect and recover | |
522 | from computer malfunctions. | |
523 | ||
524 | During normal operation, `ha-manager` regularly resets the watchdog | |
525 | timer to prevent it from elapsing. If, due to a hardware fault or | |
526 | program error, the computer fails to reset the watchdog, the timer | |
527 | will elapse and triggers a reset of the whole server (reboot). | |
528 | ||
529 | Recent server motherboards often include such hardware watchdogs, but | |
530 | these need to be configured. If no watchdog is available or | |
531 | configured, we fall back to the Linux Kernel 'softdog'. While still | |
532 | reliable, it is not independent of the servers hardware, and thus has | |
533 | a lower reliability than a hardware watchdog. | |
534 | ||
535 | ||
536 | Configure Hardware Watchdog | |
537 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
538 | ||
539 | By default, all hardware watchdog modules are blocked for security | |
540 | reasons. They are like a loaded gun if not correctly initialized. To | |
541 | enable a hardware watchdog, you need to specify the module to load in | |
542 | '/etc/default/pve-ha-manager', for example: | |
543 | ||
544 | ---- | |
545 | # select watchdog module (default is softdog) | |
546 | WATCHDOG_MODULE=iTCO_wdt | |
547 | ---- | |
548 | ||
549 | This configuration is read by the 'watchdog-mux' service, which load | |
550 | the specified module at startup. | |
551 | ||
552 | ||
553 | Recover Fenced Services | |
554 | ~~~~~~~~~~~~~~~~~~~~~~~ | |
555 | ||
556 | After a node failed and its fencing was successful, the CRM tries to | |
557 | move services from the failed node to nodes which are still online. | |
558 | ||
559 | The selection of nodes, on which those services gets recovered, is | |
560 | influenced by the resource `group` settings, the list of currently active | |
561 | nodes, and their respective active service count. | |
562 | ||
563 | The CRM first builds a set out of the intersection between user selected | |
564 | nodes (from `group` setting) and available nodes. It then choose the | |
565 | subset of nodes with the highest priority, and finally select the node | |
566 | with the lowest active service count. This minimizes the possibility | |
567 | of an overloaded node. | |
568 | ||
569 | CAUTION: On node failure, the CRM distributes services to the | |
570 | remaining nodes. This increase the service count on those nodes, and | |
571 | can lead to high load, especially on small clusters. Please design | |
572 | your cluster so that it can handle such worst case scenarios. | |
573 | ||
574 | ||
575 | [[ha_manager_start_failure_policy]] | |
576 | Start Failure Policy | |
577 | --------------------- | |
578 | ||
579 | The start failure policy comes in effect if a service failed to start on a | |
580 | node once ore more times. It can be used to configure how often a restart | |
581 | should be triggered on the same node and how often a service should be | |
582 | relocated so that it gets a try to be started on another node. | |
583 | The aim of this policy is to circumvent temporary unavailability of shared | |
584 | resources on a specific node. For example, if a shared storage isn't available | |
585 | on a quorate node anymore, e.g. network problems, but still on other nodes, | |
586 | the relocate policy allows then that the service gets started nonetheless. | |
587 | ||
588 | There are two service start recover policy settings which can be configured | |
589 | specific for each resource. | |
590 | ||
591 | max_restart:: | |
592 | ||
593 | Maximum number of tries to restart an failed service on the actual | |
594 | node. The default is set to one. | |
595 | ||
596 | max_relocate:: | |
597 | ||
598 | Maximum number of tries to relocate the service to a different node. | |
599 | A relocate only happens after the max_restart value is exceeded on the | |
600 | actual node. The default is set to one. | |
601 | ||
602 | NOTE: The relocate count state will only reset to zero when the | |
603 | service had at least one successful start. That means if a service is | |
604 | re-enabled without fixing the error only the restart policy gets | |
605 | repeated. | |
606 | ||
607 | ||
608 | [[ha_manager_error_recovery]] | |
609 | Error Recovery | |
610 | -------------- | |
611 | ||
612 | If after all tries the service state could not be recovered it gets | |
613 | placed in an error state. In this state the service won't get touched | |
614 | by the HA stack anymore. To recover from this state you should follow | |
615 | these steps: | |
616 | ||
617 | * bring the resource back into a safe and consistent state (e.g., | |
618 | killing its process) | |
619 | ||
620 | * disable the ha resource to place it in an stopped state | |
621 | ||
622 | * fix the error which led to this failures | |
623 | ||
624 | * *after* you fixed all errors you may enable the service again | |
625 | ||
626 | ||
627 | Node Maintenance | |
628 | ---------------- | |
629 | ||
630 | It is sometimes possible to shutdown or reboot a node to do | |
631 | maintenance tasks. Either to replace hardware, or simply to install a | |
632 | new kernel image. | |
633 | ||
634 | ||
635 | Shutdown | |
636 | ~~~~~~~~ | |
637 | ||
638 | A shutdown ('poweroff') is usually done if the node is planned to stay | |
639 | down for some time. The LRM stops all managed services in that | |
640 | case. This means that other nodes will take over those service | |
641 | afterwards. | |
642 | ||
643 | NOTE: Recent hardware has large amounts of RAM. So we stop all | |
644 | resources, then restart them to avoid online migration of all that | |
645 | RAM. If you want to use online migration, you need to invoke that | |
646 | manually before you shutdown the node. | |
647 | ||
648 | ||
649 | Reboot | |
650 | ~~~~~~ | |
651 | ||
652 | Node reboots are initiated with the 'reboot' command. This is usually | |
653 | done after installing a new kernel. Please note that this is different | |
654 | from ``shutdown'', because the node immediately starts again. | |
655 | ||
656 | The LRM tells the CRM that it wants to restart, and waits until the | |
657 | CRM puts all resources into the `freeze` state. This prevents that | |
658 | those resources are moved to other nodes. Instead, the CRM start the | |
659 | resources after the reboot on the same node. | |
660 | ||
661 | ||
662 | Manual Resource Movement | |
663 | ~~~~~~~~~~~~~~~~~~~~~~~~ | |
664 | ||
665 | Last but not least, you can also move resources manually to other | |
666 | nodes before you shutdown or restart a node. The advantage is that you | |
667 | have full control, and you can decide if you want to use online | |
668 | migration or not. | |
669 | ||
670 | NOTE: Please do not 'kill' services like `pve-ha-crm`, `pve-ha-lrm` or | |
671 | `watchdog-mux`. They manage and use the watchdog, so this can result | |
672 | in a node reboot. | |
673 | ||
674 | ||
675 | [[ha_manager_package_updates]] | |
676 | Package Updates | |
677 | --------------- | |
678 | ||
679 | When updating the ha-manager you should do one node after the other, never | |
680 | all at once for various reasons. First, while we test our software | |
681 | thoughtfully, a bug affecting your specific setup cannot totally be ruled out. | |
682 | Upgrading one node after the other and checking the functionality of each node | |
683 | after finishing the update helps to recover from an eventual problems, while | |
684 | updating all could render you in a broken cluster state and is generally not | |
685 | good practice. | |
686 | ||
687 | Also, the {pve} HA stack uses a request acknowledge protocol to perform | |
688 | actions between the cluster and the local resource manager. For restarting, | |
689 | the LRM makes a request to the CRM to freeze all its services. This prevents | |
690 | that they get touched by the Cluster during the short time the LRM is restarting. | |
691 | After that the LRM may safely close the watchdog during a restart. | |
692 | Such a restart happens on a update and as already stated a active master | |
693 | CRM is needed to acknowledge the requests from the LRM, if this is not the case | |
694 | the update process can be too long which, in the worst case, may result in | |
695 | a watchdog reset. | |
696 | ||
697 | ||
698 | [[ha_manager_service_operations]] | |
699 | Service Operations | |
700 | ------------------ | |
701 | ||
702 | This are how the basic user-initiated service operations (via | |
703 | `ha-manager`) work. | |
704 | ||
705 | enable:: | |
706 | ||
707 | The service will be started by the LRM if not already running. | |
708 | ||
709 | disable:: | |
710 | ||
711 | The service will be stopped by the LRM if running. | |
712 | ||
713 | migrate/relocate:: | |
714 | ||
715 | The service will be relocated (live) to another node. | |
716 | ||
717 | remove:: | |
718 | ||
719 | The service will be removed from the HA managed resource list. Its | |
720 | current state will not be touched. | |
721 | ||
722 | start/stop:: | |
723 | ||
724 | `start` and `stop` commands can be issued to the resource specific tools | |
725 | (like `qm` or `pct`), they will forward the request to the | |
726 | `ha-manager` which then will execute the action and set the resulting | |
727 | service state (enabled, disabled). | |
728 | ||
729 | ||
730 | ifdef::manvolnum[] | |
731 | include::pve-copyright.adoc[] | |
732 | endif::manvolnum[] | |
733 |