ifdef::manvolnum[]
ha-manager(1)
=============
-include::attributes.txt[]
:pve-toplevel:
NAME
ifndef::manvolnum[]
High Availability
=================
-include::attributes.txt[]
:pve-toplevel:
endif::manvolnum[]
provide such services, it is very important that they are available
most of the time.
-We can mathematically define the availability as the ratio of (A) the
+We can mathematically define the availability as the ratio of (A), the
total time a service is capable of being used during a given interval
-to (B) the length of the interval. It is normally expressed as a
+to (B), the length of the interval. It is normally expressed as a
percentage of uptime in a given year.
.Availability - Downtime per Year
There are several ways to increase availability. The most elegant
solution is to rewrite your software, so that you can run it on
-several host at the same time. The software itself need to have a way
-to detect errors and do failover. This is relatively easy if you just
-want to serve read-only web pages. But in general this is complex, and
-sometimes impossible because you cannot modify the software
-yourself. The following solutions works without modifying the
-software:
+several hosts at the same time. The software itself needs to have a way
+to detect errors and do failover. If you only want to serve read-only
+web pages, then this is relatively simple. However, this is generally complex
+and sometimes impossible, because you cannot modify the software yourself. The
+following solutions works without modifying the software:
* Use reliable ``server'' components
-
-NOTE: Computer components with same functionality can have varying
++
+NOTE: Computer components with the same functionality can have varying
reliability numbers, depending on the component quality. Most vendors
sell components with higher reliability as ``server'' components -
usually at higher price.
* Eliminate single point of failure (redundant components)
** use an uninterruptible power supply (UPS)
-** use redundant power supplies on the main boards
+** use redundant power supplies in your servers
** use ECC-RAM
** use redundant network hardware
** use RAID for local storage
Virtualization environments like {pve} make it much easier to reach
high availability because they remove the ``hardware'' dependency. They
-also support to setup and use redundant storage and network
-devices. So if one host fail, you can simply start those services on
+also support the setup and use of redundant storage and network
+devices, so if one host fails, you can simply start those services on
another host within your cluster.
-Even better, {pve} provides a software stack called `ha-manager`,
+Better still, {pve} provides a software stack called `ha-manager`,
which can do that automatically for you. It is able to automatically
detect errors and do automatic failover.
{pve} `ha-manager` works like an ``automated'' administrator. First, you
configure what resources (VMs, containers, ...) it should
-manage. `ha-manager` then observes correct functionality, and handles
+manage. Then, `ha-manager` observes the correct functionality, and handles
service failover to another node in case of errors. `ha-manager` can
also handle normal user requests which may start, stop, relocate and
migrate a service.
But high availability comes at a price. High quality components are
-more expensive, and making them redundant duplicates the costs at
+more expensive, and making them redundant doubles the costs at
least. Additional spare parts increase costs further. So you should
carefully calculate the benefits, and compare with those additional
costs.
TIP: Increasing availability from 99% to 99.9% is relatively
-simply. But increasing availability from 99.9999% to 99.99999% is very
+simple. But increasing availability from 99.9999% to 99.99999% is very
hard and costly. `ha-manager` has typical error detection and failover
times of about 2 minutes, so you can get no more than 99.999%
availability.
+
Requirements
------------
+You must meet the following requirements before you start with HA:
+
* at least three cluster nodes (to get reliable quorum)
* shared storage for VMs and containers
* hardware redundancy (everywhere)
+* use reliable “server” components
+
* hardware watchdog - if not available we fall back to the
linux kernel software watchdog (`softdog`)
We call the primary management unit handled by `ha-manager` a
resource. A resource (also called ``service'') is uniquely
identified by a service ID (SID), which consists of the resource type
-and an type specific ID, e.g.: `vm:100`. That example would be a
+and a type specific ID, for example `vm:100`. That example would be a
resource of type `vm` (virtual machine) with the ID 100.
For now we have two important resources types - virtual machines and
containers. One basic idea here is that we can bundle related software
-into such VM or container, so there is no need to compose one big
-service from other services, like it was done with `rgmanager`. In
-general, a HA enabled resource should not depend on other resources.
+into such a VM or container, so there is no need to compose one big
+service from other services, as was done with `rgmanager`. In
+general, a HA managed resource should not depend on other resources.
+
+
+Management Tasks
+----------------
+
+This section provides a short overview of common management tasks. The
+first step is to enable HA for a resource. This is done by adding the
+resource to the HA resource configuration. You can do this using the
+GUI, or simply use the command-line tool, for example:
+
+----
+# ha-manager add vm:100
+----
+
+The HA stack now tries to start the resources and keep them
+running. Please note that you can configure the ``requested''
+resources state. For example you may want the HA stack to stop the
+resource:
+
+----
+# ha-manager set vm:100 --state stopped
+----
+
+and start it again later:
+
+----
+# ha-manager set vm:100 --state started
+----
+
+You can also use the normal VM and container management commands. They
+automatically forward the commands to the HA stack, so
+
+----
+# qm start 100
+----
+
+simply sets the requested state to `started`. The same applies to `qm
+stop`, which sets the requested state to `stopped`.
+
+NOTE: The HA stack works fully asynchronous and needs to communicate
+with other cluster members. Therefore, it takes some seconds until you see
+the result of such actions.
+
+To view the current HA resource configuration use:
+
+----
+# ha-manager config
+vm:100
+ state stopped
+----
+
+And you can view the actual HA manager and resource state with:
+
+----
+# ha-manager status
+quorum OK
+master node1 (active, Wed Nov 23 11:07:23 2016)
+lrm elsa (active, Wed Nov 23 11:07:19 2016)
+service vm:100 (node1, started)
+----
+
+You can also initiate resource migration to other nodes:
+
+----
+# ha-manager migrate vm:100 node2
+----
+
+This uses online migration and tries to keep the VM running. Online
+migration needs to transfer all used memory over the network, so it is
+sometimes faster to stop the VM, then restart it on the new node. This can be
+done using the `relocate` command:
+
+----
+# ha-manager relocate vm:100 node2
+----
+
+Finally, you can remove the resource from the HA configuration using
+the following command:
+
+----
+# ha-manager remove vm:100
+----
+
+NOTE: This does not start or stop the resource.
+
+But all HA related tasks can be done in the GUI, so there is no need to
+use the command line at all.
How It Works
------------
-This section provides an in detail description of the {PVE} HA-manager
-internals. It describes how the CRM and the LRM work together.
-
-To provide High Availability two daemons run on each node:
+This section provides a detailed description of the {PVE} HA manager
+internals. It describes all involved daemons and how they work
+together. To provide HA, two daemons run on each node:
`pve-ha-lrm`::
-The local resource manager (LRM), it controls the services running on
-the local node.
-It reads the requested states for its services from the current manager
-status file and executes the respective commands.
+The local resource manager (LRM), which controls the services running on
+the local node. It reads the requested states for its services from
+the current manager status file and executes the respective commands.
`pve-ha-crm`::
-The cluster resource manager (CRM), it controls the cluster wide
-actions of the services, processes the LRM results and includes the state
-machine which controls the state of each service.
+The cluster resource manager (CRM), which makes the cluster-wide
+decisions. It sends commands to the LRM, processes the results,
+and moves resources to other nodes if something fails. The CRM also
+handles node fencing.
+
.Locks in the LRM & CRM
[NOTE]
Locks are provided by our distributed configuration file system (pmxcfs).
-They are used to guarantee that each LRM is active once and working. As a
-LRM only executes actions when it holds its lock we can mark a failed node
-as fenced if we can acquire its lock. This lets us then recover any failed
+They are used to guarantee that each LRM is active once and working. As an
+LRM only executes actions when it holds its lock, we can mark a failed node
+as fenced if we can acquire its lock. This then lets us recover any failed
HA services securely without any interference from the now unknown failed node.
-This all gets supervised by the CRM which holds currently the manager master
+This all gets supervised by the CRM which currently holds the manager master
lock.
+
+[[ha_manager_service_states]]
+Service States
+~~~~~~~~~~~~~~
+
+The CRM uses a service state enumeration to record the current service
+state. This state is displayed on the GUI and can be queried using
+the `ha-manager` command-line tool:
+
+----
+# ha-manager status
+quorum OK
+master elsa (active, Mon Nov 21 07:23:29 2016)
+lrm elsa (active, Mon Nov 21 07:23:22 2016)
+service ct:100 (elsa, stopped)
+service ct:102 (elsa, started)
+service vm:501 (elsa, started)
+----
+
+Here is the list of possible states:
+
+stopped::
+
+Service is stopped (confirmed by LRM). If the LRM detects a stopped
+service is still running, it will stop it again.
+
+request_stop::
+
+Service should be stopped. The CRM waits for confirmation from the
+LRM.
+
+stopping::
+
+Pending stop request. But the CRM did not get the request so far.
+
+started::
+
+Service is active an LRM should start it ASAP if not already running.
+If the Service fails and is detected to be not running the LRM
+restarts it
+(see xref:ha_manager_start_failure_policy[Start Failure Policy]).
+
+starting::
+
+Pending start request. But the CRM has not got any confirmation from the
+LRM that the service is running.
+
+fence::
+
+Wait for node fencing as the service node is not inside the quorate cluster
+partition (see xref:ha_manager_fencing[Fencing]).
+As soon as node gets fenced successfully the service will be placed into the
+recovery state.
+
+recovery::
+
+Wait for recovery of the service. The HA manager tries to find a new node where
+the service can run on. This search depends not only on the list of online and
+quorate nodes, but also if the service is a group member and how such a group
+is limited.
+As soon as a new available node is found, the service will be moved there and
+initially placed into stopped state. If it's configured to run the new node
+will do so.
+
+freeze::
+
+Do not touch the service state. We use this state while we reboot a
+node, or when we restart the LRM daemon
+(see xref:ha_manager_package_updates[Package Updates]).
+
+ignored::
+
+Act as if the service were not managed by HA at all.
+Useful, when full control over the service is desired temporarily, without
+removing it from the HA configuration.
+
+migrate::
+
+Migrate service (live) to other node.
+
+error::
+
+Service is disabled because of LRM errors. Needs manual intervention
+(see xref:ha_manager_error_recovery[Error Recovery]).
+
+queued::
+
+Service is newly added, and the CRM has not seen it so far.
+
+disabled::
+
+Service is stopped and marked as `disabled`
+
+
+[[ha_manager_lrm]]
Local Resource Manager
~~~~~~~~~~~~~~~~~~~~~~
The local resource manager (`pve-ha-lrm`) is started as a daemon on
-boot and waits until the HA cluster is quorate and thus cluster wide
+boot and waits until the HA cluster is quorate and thus cluster-wide
locks are working.
It can be in three states:
After the LRM gets in the active state it reads the manager status
file in `/etc/pve/ha/manager_status` and determines the commands it
has to execute for the services it owns.
-For each command a worker gets started, this workers are running in
+For each command a worker gets started, these workers are running in
parallel and are limited to at most 4 by default. This default setting
may be changed through the datacenter configuration key `max_worker`.
When finished the worker process gets collected and its result saved for
.Maximum Concurrent Worker Adjustment Tips
[NOTE]
The default value of at most 4 concurrent workers may be unsuited for
-a specific setup. For example may 4 live migrations happen at the same
+a specific setup. For example, 4 live migrations may occur at the same
time, which can lead to network congestions with slower networks and/or
-big (memory wise) services. Ensure that also in the worst case no congestion
-happens and lower the `max_worker` value if needed. In the contrary, if you
-have a particularly powerful high end setup you may also want to increase it.
+big (memory wise) services. Also, ensure that in the worst case, congestion is
+at a minimum, even if this means lowering the `max_worker` value. On the
+contrary, if you have a particularly powerful, high-end setup you may also want
+to increase it.
-Each command requested by the CRM is uniquely identifiable by an UID, when
-the worker finished its result will be processed and written in the LRM
+Each command requested by the CRM is uniquely identifiable by a UID. When
+the worker finishes, its result will be processed and written in the LRM
status file `/etc/pve/nodes/<nodename>/lrm_status`. There the CRM may collect
-it and let its state machine - respective the commands output - act on it.
+it and let its state machine - respective to the commands output - act on it.
The actions on each service between CRM and LRM are normally always synced.
-This means that the CRM requests a state uniquely marked by an UID, the LRM
-then executes this action *one time* and writes back the result, also
+This means that the CRM requests a state uniquely marked by a UID, the LRM
+then executes this action *one time* and writes back the result, which is also
identifiable by the same UID. This is needed so that the LRM does not
-executes an outdated command.
-With the exception of the `stop` and the `error` command,
-those two do not depend on the result produced and are executed
+execute an outdated command.
+The only exceptions to this behaviour are the `stop` and `error` commands;
+these two do not depend on the result produced and are executed
always in the case of the stopped state and once in the case of
the error state.
`journalctl -u pve-ha-lrm` on the node(s) where the service is and
the same command for the pve-ha-crm on the node which is the current master.
+
+[[ha_manager_crm]]
Cluster Resource Manager
~~~~~~~~~~~~~~~~~~~~~~~~
The CRM lost its lock, this means a failure happened and quorum was lost.
-It main task is to manage the services which are configured to be highly
-available and try to always enforce them to the wanted state, e.g.: a
-enabled service will be started if its not running, if it crashes it will
-be started again. Thus it dictates the LRM the actions it needs to execute.
+Its main task is to manage the services which are configured to be highly
+available and try to always enforce the requested state. For example, a
+service with the requested state 'started' will be started if its not
+already running. If it crashes it will be automatically started again.
+Thus the CRM dictates the actions the LRM needs to execute.
-When an node leaves the cluster quorum, its state changes to unknown.
-If the current CRM then can secure the failed nodes lock, the services
+When a node leaves the cluster quorum, its state changes to unknown.
+If the current CRM can then secure the failed node's lock, the services
will be 'stolen' and restarted on another node.
When a cluster member determines that it is no longer in the cluster
quorum, the LRM waits for a new quorum to form. As long as there is no
quorum the node cannot reset the watchdog. This will trigger a reboot
-after the watchdog then times out, this happens after 60 seconds.
+after the watchdog times out (this happens after 60 seconds).
+
+
+HA Simulator
+------------
+
+[thumbnail="screenshot/gui-ha-manager-status.png"]
+
+By using the HA simulator you can test and learn all functionalities of the
+Proxmox VE HA solutions.
+
+By default, the simulator allows you to watch and test the behaviour of a
+real-world 3 node cluster with 6 VMs. You can also add or remove additional VMs
+or Container.
+
+You do not have to setup or configure a real cluster, the HA simulator runs out
+of the box.
+
+Install with apt:
+
+----
+apt install pve-ha-simulator
+----
+
+You can even install the package on any Debian-based system without any
+other Proxmox VE packages. For that you will need to download the package and
+copy it to the system you want to run it on for installation. When you install
+the package with apt from the local file system it will also resolve the
+required dependencies for you.
+
+
+To start the simulator on a remote machine you must have an X11 redirection to
+your current system.
+
+If you are on a Linux machine you can use:
+
+----
+ssh root@<IPofPVE> -Y
+----
+
+On Windows it works with https://mobaxterm.mobatek.net/[mobaxterm].
+
+After connecting to an existing {pve} with the simulator installed or
+installing it on your local Debian-based system manually, you can try it out as
+follows.
+
+First you need to create a working directory where the simulator saves its
+current state and writes its default config:
+
+----
+mkdir working
+----
+
+Then, simply pass the created directory as a parameter to 'pve-ha-simulator':
+
+----
+pve-ha-simulator working/
+----
+
+You can then start, stop, migrate the simulated HA services, or even check out
+what happens on a node failure.
Configuration
-------------
-The HA stack is well integrated in the Proxmox VE API2. So, for
-example, HA can be configured via `ha-manager` or the PVE web
-interface, which both provide an easy to use tool.
+The HA stack is well integrated into the {pve} API. So, for example,
+HA can be configured via the `ha-manager` command-line interface, or
+the {pve} web interface - both interfaces provide an easy way to
+manage HA. Automation tools can use the API directly.
-The resource configuration file can be located at
-`/etc/pve/ha/resources.cfg` and the group configuration file at
-`/etc/pve/ha/groups.cfg`. Use the provided tools to make changes,
-there shouldn't be any need to edit them manually.
+All HA configuration files are within `/etc/pve/ha/`, so they get
+automatically distributed to the cluster nodes, and all nodes share
+the same HA configuration.
-Node Power Status
------------------
-If a node needs maintenance you should migrate and or relocate all
-services which are required to run always on another node first.
-After that you can stop the LRM and CRM services. But note that the
-watchdog triggers if you stop it with active services.
+[[ha_manager_resource_config]]
+Resources
+~~~~~~~~~
-Package Updates
----------------
+[thumbnail="screenshot/gui-ha-manager-status.png"]
-When updating the ha-manager you should do one node after the other, never
-all at once for various reasons. First, while we test our software
-thoughtfully, a bug affecting your specific setup cannot totally be ruled out.
-Upgrading one node after the other and checking the functionality of each node
-after finishing the update helps to recover from an eventual problems, while
-updating all could render you in a broken cluster state and is generally not
-good practice.
-Also, the {pve} HA stack uses a request acknowledge protocol to perform
-actions between the cluster and the local resource manager. For restarting,
-the LRM makes a request to the CRM to freeze all its services. This prevents
-that they get touched by the Cluster during the short time the LRM is restarting.
-After that the LRM may safely close the watchdog during a restart.
-Such a restart happens on a update and as already stated a active master
-CRM is needed to acknowledge the requests from the LRM, if this is not the case
-the update process can be too long which, in the worst case, may result in
-a watchdog reset.
+The resource configuration file `/etc/pve/ha/resources.cfg` stores
+the list of resources managed by `ha-manager`. A resource configuration
+inside that list looks like this:
+
+----
+<type>: <name>
+ <property> <value>
+ ...
+----
+
+It starts with a resource type followed by a resource specific name,
+separated with colon. Together this forms the HA resource ID, which is
+used by all `ha-manager` commands to uniquely identify a resource
+(example: `vm:100` or `ct:101`). The next lines contain additional
+properties:
+
+include::ha-resources-opts.adoc[]
+
+Here is a real world example with one VM and one container. As you see,
+the syntax of those files is really simple, so it is even possible to
+read or edit those files using your favorite editor:
+
+.Configuration Example (`/etc/pve/ha/resources.cfg`)
+----
+vm: 501
+ state started
+ max_relocate 2
+
+ct: 102
+ # Note: use default settings for everything
+----
+
+[thumbnail="screenshot/gui-ha-manager-add-resource.png"]
+
+The above config was generated using the `ha-manager` command-line tool:
+
+----
+# ha-manager add vm:501 --state started --max_relocate 2
+# ha-manager add ct:102
+----
+
+
+[[ha_manager_groups]]
+Groups
+~~~~~~
+
+[thumbnail="screenshot/gui-ha-manager-groups-view.png"]
+
+The HA group configuration file `/etc/pve/ha/groups.cfg` is used to
+define groups of cluster nodes. A resource can be restricted to run
+only on the members of such group. A group configuration look like
+this:
+
+----
+group: <group>
+ nodes <node_list>
+ <property> <value>
+ ...
+----
+
+include::ha-groups-opts.adoc[]
+
+[thumbnail="screenshot/gui-ha-manager-add-group.png"]
+
+A common requirement is that a resource should run on a specific
+node. Usually the resource is able to run on other nodes, so you can define
+an unrestricted group with a single member:
+
+----
+# ha-manager groupadd prefer_node1 --nodes node1
+----
+
+For bigger clusters, it makes sense to define a more detailed failover
+behavior. For example, you may want to run a set of services on
+`node1` if possible. If `node1` is not available, you want to run them
+equally split on `node2` and `node3`. If those nodes also fail, the
+services should run on `node4`. To achieve this you could set the node
+list to:
+
+----
+# ha-manager groupadd mygroup1 -nodes "node1:2,node2:1,node3:1,node4"
+----
+
+Another use case is if a resource uses other resources only available
+on specific nodes, lets say `node1` and `node2`. We need to make sure
+that HA manager does not use other nodes, so we need to create a
+restricted group with said nodes:
+
+----
+# ha-manager groupadd mygroup2 -nodes "node1,node2" -restricted
+----
+
+The above commands created the following group configuration file:
+
+.Configuration Example (`/etc/pve/ha/groups.cfg`)
+----
+group: prefer_node1
+ nodes node1
+
+group: mygroup1
+ nodes node2:1,node4,node1:2,node3:1
+
+group: mygroup2
+ nodes node2,node1
+ restricted 1
+----
+
+
+The `nofailback` options is mostly useful to avoid unwanted resource
+movements during administration tasks. For example, if you need to
+migrate a service to a node which doesn't have the highest priority in the
+group, you need to tell the HA manager not to instantly move this service
+back by setting the `nofailback` option.
+
+Another scenario is when a service was fenced and it got recovered to
+another node. The admin tries to repair the fenced node and brings it
+up online again to investigate the cause of failure and check if it runs
+stably again. Setting the `nofailback` flag prevents the recovered services from
+moving straight back to the fenced node.
[[ha_manager_fencing]]
Fencing
-------
-What is Fencing
-~~~~~~~~~~~~~~~
+On node failures, fencing ensures that the erroneous node is
+guaranteed to be offline. This is required to make sure that no
+resource runs twice when it gets recovered on another node. This is a
+really important task, because without this, it would not be possible to
+recover a resource on another node.
+
+If a node did not get fenced, it would be in an unknown state where
+it may have still access to shared resources. This is really
+dangerous! Imagine that every network but the storage one broke. Now,
+while not reachable from the public network, the VM still runs and
+writes to the shared storage.
-Fencing secures that on a node failure the dangerous node gets will be rendered
-unable to do any damage and that no resource runs twice when it gets recovered
-from the failed node. This is a really important task and one of the base
-principles to make a system Highly Available.
+If we then simply start up this VM on another node, we would get a
+dangerous race condition, because we write from both nodes. Such
+conditions can destroy all VM data and the whole VM could be rendered
+unusable. The recovery could also fail if the storage protects against
+multiple mounts.
-If a node would not get fenced it would be in an unknown state where it may
-have still access to shared resources, this is really dangerous!
-Imagine that every network but the storage one broke, now while not
-reachable from the public network the VM still runs and writes on the shared
-storage. If we would not fence the node and just start up this VM on another
-Node we would get dangerous race conditions, atomicity violations the whole VM
-could be rendered unusable. The recovery could also simply fail if the storage
-protects from multiple mounts and thus defeat the purpose of HA.
How {pve} Fences
-~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~
-There are different methods to fence a node, for example fence devices which
-cut off the power from the node or disable their communication completely.
+There are different methods to fence a node, for example, fence
+devices which cut off the power from the node or disable their
+communication completely. Those are often quite expensive and bring
+additional critical components into a system, because if they fail you
+cannot recover any service.
-Those are often quite expensive and bring additional critical components in
-a system, because if they fail you cannot recover any service.
+We thus wanted to integrate a simpler fencing method, which does not
+require additional external hardware. This can be done using
+watchdog timers.
-We thus wanted to integrate a simpler method in the HA Manager first, namely
-self fencing with watchdogs.
+.Possible Fencing Methods
+- external power switches
+- isolate nodes by disabling complete network traffic on the switch
+- self fencing using watchdog timers
-Watchdogs are widely used in critical and dependable systems since the
-beginning of micro controllers, they are often independent and simple
-integrated circuit which programs can use to watch them. After opening they need to
-report periodically. If, for whatever reason, a program becomes unable to do
-so the watchdogs triggers a reset of the whole server.
+Watchdog timers have been widely used in critical and dependable systems
+since the beginning of microcontrollers. They are often simple, independent
+integrated circuits which are used to detect and recover from computer malfunctions.
+
+During normal operation, `ha-manager` regularly resets the watchdog
+timer to prevent it from elapsing. If, due to a hardware fault or
+program error, the computer fails to reset the watchdog, the timer
+will elapse and trigger a reset of the whole server (reboot).
+
+Recent server motherboards often include such hardware watchdogs, but
+these need to be configured. If no watchdog is available or
+configured, we fall back to the Linux Kernel 'softdog'. While still
+reliable, it is not independent of the servers hardware, and thus has
+a lower reliability than a hardware watchdog.
-Server motherboards often already include such hardware watchdogs, these need
-to be configured. If no watchdog is available or configured we fall back to the
-Linux Kernel softdog while still reliable it is not independent of the servers
-Hardware and thus has a lower reliability then a hardware watchdog.
Configure Hardware Watchdog
~~~~~~~~~~~~~~~~~~~~~~~~~~~
-By default all watchdog modules are blocked for security reasons as they are
-like a loaded gun if not correctly initialized.
-If you have a hardware watchdog available remove its kernel module from the
-blacklist, load it with insmod and restart the `watchdog-mux` service or reboot
-the node.
+
+By default, all hardware watchdog modules are blocked for security
+reasons. They are like a loaded gun if not correctly initialized. To
+enable a hardware watchdog, you need to specify the module to load in
+'/etc/default/pve-ha-manager', for example:
+
+----
+# select watchdog module (default is softdog)
+WATCHDOG_MODULE=iTCO_wdt
+----
+
+This configuration is read by the 'watchdog-mux' service, which loads
+the specified module at startup.
+
Recover Fenced Services
~~~~~~~~~~~~~~~~~~~~~~~
-After a node failed and its fencing was successful we start to recover services
-to other available nodes and restart them there so that they can provide service
-again.
-
-The selection of the node on which the services gets recovered is influenced
-by the users group settings, the currently active nodes and their respective
-active service count.
-First we build a set out of the intersection between user selected nodes and
-available nodes. Then the subset with the highest priority of those nodes
-gets chosen as possible nodes for recovery. We select the node with the
-currently lowest active service count as a new node for the service.
-That minimizes the possibility of an overload, which else could cause an
-unresponsive node and as a result a chain reaction of node failures in the
-cluster.
+After a node failed and its fencing was successful, the CRM tries to
+move services from the failed node to nodes which are still online.
-[[ha_manager_groups]]
-Groups
-------
+The selection of nodes, on which those services gets recovered, is
+influenced by the resource `group` settings, the list of currently active
+nodes, and their respective active service count.
-A group is a collection of cluster nodes which a service may be bound to.
-
-Group Settings
-~~~~~~~~~~~~~~
+The CRM first builds a set out of the intersection between user selected
+nodes (from `group` setting) and available nodes. It then choose the
+subset of nodes with the highest priority, and finally select the node
+with the lowest active service count. This minimizes the possibility
+of an overloaded node.
-nodes::
-
-List of group node members where a priority can be given to each node.
-A service bound to this group will run on the nodes with the highest priority
-available. If more nodes are in the highest priority class the services will
-get distributed to those node if not already there. The priorities have a
-relative meaning only.
- Example;;
- You want to run all services from a group on `node1` if possible. If this node
- is not available, you want them to run equally splitted on `node2` and `node3`, and
- if those fail it should use `node4`.
- To achieve this you could set the node list to:
-[source,bash]
- ha-manager groupset mygroup -nodes "node1:2,node2:1,node3:1,node4"
-
-restricted::
-
-Resources bound to this group may only run on nodes defined by the
-group. If no group node member is available the resource will be
-placed in the stopped state.
- Example;;
- Lets say a service uses resources only available on `node1` and `node2`,
- so we need to make sure that HA manager does not use other nodes.
- We need to create a 'restricted' group with said nodes:
-[source,bash]
- ha-manager groupset mygroup -nodes "node1,node2" -restricted
-
-nofailback::
-
-The resource won't automatically fail back when a more preferred node
-(re)joins the cluster.
- Examples;;
- * You need to migrate a service to a node which hasn't the highest priority
- in the group at the moment, to tell the HA manager to not move this service
- instantly back set the 'nofailback' option and the service will stay on
- the current node.
-
- * A service was fenced and it got recovered to another node. The admin
- repaired the node and brought it up online again but does not want that the
- recovered services move straight back to the repaired node as he wants to
- first investigate the failure cause and check if it runs stable. He can use
- the 'nofailback' option to achieve this.
+CAUTION: On node failure, the CRM distributes services to the
+remaining nodes. This increases the service count on those nodes, and
+can lead to high load, especially on small clusters. Please design
+your cluster so that it can handle such worst case scenarios.
+[[ha_manager_start_failure_policy]]
Start Failure Policy
---------------------
-The start failure policy comes in effect if a service failed to start on a
-node once ore more times. It can be used to configure how often a restart
+The start failure policy comes into effect if a service failed to start on a
+node one or more times. It can be used to configure how often a restart
should be triggered on the same node and how often a service should be
-relocated so that it gets a try to be started on another node.
+relocated, so that it has an attempt to be started on another node.
The aim of this policy is to circumvent temporary unavailability of shared
resources on a specific node. For example, if a shared storage isn't available
-on a quorate node anymore, e.g. network problems, but still on other nodes,
-the relocate policy allows then that the service gets started nonetheless.
+on a quorate node anymore, for instance due to network problems, but is still
+available on other nodes, the relocate policy allows the service to start
+nonetheless.
There are two service start recover policy settings which can be configured
specific for each resource.
max_restart::
-Maximum number of tries to restart an failed service on the actual
+Maximum number of attempts to restart a failed service on the actual
node. The default is set to one.
max_relocate::
-Maximum number of tries to relocate the service to a different node.
+Maximum number of attempts to relocate the service to a different node.
A relocate only happens after the max_restart value is exceeded on the
actual node. The default is set to one.
NOTE: The relocate count state will only reset to zero when the
service had at least one successful start. That means if a service is
-re-enabled without fixing the error only the restart policy gets
+re-started without fixing the error only the restart policy gets
repeated.
+
+[[ha_manager_error_recovery]]
Error Recovery
--------------
-If after all tries the service state could not be recovered it gets
-placed in an error state. In this state the service won't get touched
-by the HA stack anymore. To recover from this state you should follow
-these steps:
+If, after all attempts, the service state could not be recovered, it gets
+placed in an error state. In this state, the service won't get touched
+by the HA stack anymore. The only way out is disabling a service:
+
+----
+# ha-manager set vm:100 --state disabled
+----
+
+This can also be done in the web interface.
+
+To recover from the error state you should do the following:
-* bring the resource back into a safe and consistent state (e.g.,
-killing its process)
+* bring the resource back into a safe and consistent state (e.g.:
+kill its process if the service could not be stopped)
-* disable the ha resource to place it in an stopped state
+* disable the resource to remove the error flag
* fix the error which led to this failures
-* *after* you fixed all errors you may enable the service again
+* *after* you fixed all errors you may request that the service starts again
-[[ha_manager_service_operations]]
-Service Operations
-------------------
+[[ha_manager_package_updates]]
+Package Updates
+---------------
-This are how the basic user-initiated service operations (via
-`ha-manager`) work.
+When updating the ha-manager, you should do one node after the other, never
+all at once for various reasons. First, while we test our software
+thoroughly, a bug affecting your specific setup cannot totally be ruled out.
+Updating one node after the other and checking the functionality of each node
+after finishing the update helps to recover from eventual problems, while
+updating all at once could result in a broken cluster and is generally not
+good practice.
-enable::
+Also, the {pve} HA stack uses a request acknowledge protocol to perform
+actions between the cluster and the local resource manager. For restarting,
+the LRM makes a request to the CRM to freeze all its services. This prevents
+them from getting touched by the Cluster during the short time the LRM is restarting.
+After that, the LRM may safely close the watchdog during a restart.
+Such a restart happens normally during a package update and, as already stated,
+an active master CRM is needed to acknowledge the requests from the LRM. If
+this is not the case the update process can take too long which, in the worst
+case, may result in a reset triggered by the watchdog.
-The service will be started by the LRM if not already running.
-disable::
+[[ha_manager_node_maintenance]]
+Node Maintenance
+----------------
-The service will be stopped by the LRM if running.
+Sometimes it is necessary to perform maintenance on a node, such as replacing
+hardware or simply installing a new kernel image. This also applies while the
+HA stack is in use.
-migrate/relocate::
+The HA stack can support you mainly in two types of maintenance:
-The service will be relocated (live) to another node.
+* for general shutdowns or reboots, the behavior can be configured, see
+ xref:ha_manager_shutdown_policy[Shutdown Policy].
+* for maintenance that does not require a shutdown or reboot, or that should
+ not be switched off automatically after only one reboot, you can enable the
+ manual maintenance mode.
-remove::
-The service will be removed from the HA managed resource list. Its
-current state will not be touched.
+Maintenance Mode
+~~~~~~~~~~~~~~~~
-start/stop::
+You can use the manual maintenance mode to mark the node as unavailable for HA
+operation, prompting all services managed by HA to migrate to other nodes.
-`start` and `stop` commands can be issued to the resource specific tools
-(like `qm` or `pct`), they will forward the request to the
-`ha-manager` which then will execute the action and set the resulting
-service state (enabled, disabled).
+The target nodes for these migrations are selected from the other currently
+available nodes, and determined by the HA group configuration and the configured
+cluster resource scheduler (CRS) mode.
+During each migration, the original node will be recorded in the HA managers'
+state, so that the service can be moved back again automatically once the
+maintenance mode is disabled and the node is back online.
+Currently you can enabled or disable the maintenance mode using the ha-manager
+CLI tool.
-Service States
---------------
+.Enabling maintenance mode for a node
+----
+# ha-manager crm-command node-maintenance enable NODENAME
+----
-stopped::
+This will queue a CRM command, when the manager processes this command it will
+record the request for maintenance-mode in the manager status. This allows you
+to submit the command on any node, not just on the one you want to place in, or
+out of the maintenance mode.
-Service is stopped (confirmed by LRM), if detected running it will get stopped
-again.
+Once the LRM on the respective node picks the command up it will mark itself as
+unavailable, but still process all migration commands. This means that the LRM
+self-fencing watchdog will stay active until all active services got moved, and
+all running workers finished.
-request_stop::
+Note that the LRM status will read `maintenance` mode as soon as the LRM
+picked the requested state up, not only when all services got moved away, this
+user experience is planned to be improved in the future.
+For now, you can check for any active HA service left on the node, or watching
+out for a log line like: `pve-ha-lrm[PID]: watchdog closed (disabled)` to know
+when the node finished its transition into the maintenance mode.
-Service should be stopped. Waiting for confirmation from LRM.
+NOTE: The manual maintenance mode is not automatically deleted on node reboot,
+but only if it is either manually deactivated using the `ha-manager` CLI or if
+the manager-status is manually cleared.
-started::
+.Disabling maintenance mode for a node
+----
+# ha-manager crm-command node-maintenance disable NODENAME
+----
-Service is active an LRM should start it ASAP if not already running.
-If the Service fails and is detected to be not running the LRM restarts it.
+The process of disabling the manual maintenance mode is similar to enabling it.
+Using the `ha-manager` CLI command shown above will queue a CRM command that,
+once processed, marks the respective LRM node as available again.
-fence::
+If you deactivate the maintenance mode, all services that were on the node when
+the maintenance mode was activated will be moved back.
-Wait for node fencing (service node is not inside quorate cluster
-partition).
-As soon as node gets fenced successfully the service will be recovered to
-another node, if possible.
+[[ha_manager_shutdown_policy]]
+Shutdown Policy
+~~~~~~~~~~~~~~~
-freeze::
+Below you will find a description of the different HA policies for a node
+shutdown. Currently 'Conditional' is the default due to backward compatibility.
+Some users may find that 'Migrate' behaves more as expected.
-Do not touch the service state. We use this state while we reboot a
-node, or when we restart the LRM daemon.
+The shutdown policy can be configured in the Web UI (`Datacenter` -> `Options`
+-> `HA Settings`), or directly in `datacenter.cfg`:
-migrate::
+----
+ha: shutdown_policy=<value>
+----
-Migrate service (live) to other node.
+Migrate
+^^^^^^^
-error::
+Once the Local Resource manager (LRM) gets a shutdown request and this policy
+is enabled, it will mark itself as unavailable for the current HA manager.
+This triggers a migration of all HA Services currently located on this node.
+The LRM will try to delay the shutdown process, until all running services get
+moved away. But, this expects that the running services *can* be migrated to
+another node. In other words, the service must not be locally bound, for example
+by using hardware passthrough. As non-group member nodes are considered as
+runnable target if no group member is available, this policy can still be used
+when making use of HA groups with only some nodes selected. But, marking a group
+as 'restricted' tells the HA manager that the service cannot run outside of the
+chosen set of nodes. If all of those nodes are unavailable, the shutdown will
+hang until you manually intervene. Once the shut down node comes back online
+again, the previously displaced services will be moved back, if they were not
+already manually migrated in-between.
+
+NOTE: The watchdog is still active during the migration process on shutdown.
+If the node loses quorum it will be fenced and the services will be recovered.
+
+If you start a (previously stopped) service on a node which is currently being
+maintained, the node needs to be fenced to ensure that the service can be moved
+and started on another available node.
+
+Failover
+^^^^^^^^
+
+This mode ensures that all services get stopped, but that they will also be
+recovered, if the current node is not online soon. It can be useful when doing
+maintenance on a cluster scale, where live-migrating VMs may not be possible if
+too many nodes are powered off at a time, but you still want to ensure HA
+services get recovered and started again as soon as possible.
+
+Freeze
+^^^^^^
+
+This mode ensures that all services get stopped and frozen, so that they won't
+get recovered until the current node is online again.
+
+Conditional
+^^^^^^^^^^^
+
+The 'Conditional' shutdown policy automatically detects if a shutdown or a
+reboot is requested, and changes behaviour accordingly.
+
+.Shutdown
+
+A shutdown ('poweroff') is usually done if it is planned for the node to stay
+down for some time. The LRM stops all managed services in this case. This means
+that other nodes will take over those services afterwards.
+
+NOTE: Recent hardware has large amounts of memory (RAM). So we stop all
+resources, then restart them to avoid online migration of all that RAM. If you
+want to use online migration, you need to invoke that manually before you
+shutdown the node.
+
+
+.Reboot
+
+Node reboots are initiated with the 'reboot' command. This is usually done
+after installing a new kernel. Please note that this is different from
+``shutdown'', because the node immediately starts again.
+
+The LRM tells the CRM that it wants to restart, and waits until the CRM puts
+all resources into the `freeze` state (same mechanism is used for
+xref:ha_manager_package_updates[Package Updates]). This prevents those resources
+from being moved to other nodes. Instead, the CRM starts the resources after the
+reboot on the same node.
+
+
+Manual Resource Movement
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Last but not least, you can also manually move resources to other nodes, before
+you shutdown or restart a node. The advantage is that you have full control,
+and you can decide if you want to use online migration or not.
+
+NOTE: Please do not 'kill' services like `pve-ha-crm`, `pve-ha-lrm` or
+`watchdog-mux`. They manage and use the watchdog, so this can result in an
+immediate node reboot or even reset.
+
+
+[[ha_manager_crs]]
+Cluster Resource Scheduling
+---------------------------
+
+The cluster resource scheduler (CRS) mode controls how HA selects nodes for the
+recovery of a service as well as for migrations that are triggered by a
+shutdown policy. The default mode is `basic`, you can change it in the Web UI
+(`Datacenter` -> `Options`), or directly in `datacenter.cfg`:
+
+----
+crs: ha=static
+----
+
+[thumbnail="screenshot/gui-datacenter-options-crs.png"]
+
+The change will be in effect starting with the next manager round (after a few
+seconds).
+
+For each service that needs to be recovered or migrated, the scheduler
+iteratively chooses the best node among the nodes with the highest priority in
+the service's group.
+
+NOTE: There are plans to add modes for (static and dynamic) load-balancing in
+the future.
+
+Basic Scheduler
+~~~~~~~~~~~~~~~
+
+The number of active HA services on each node is used to choose a recovery node.
+Non-HA-managed services are currently not counted.
+
+Static-Load Scheduler
+~~~~~~~~~~~~~~~~~~~~~
+
+IMPORTANT: The static mode is still a technology preview.
+
+Static usage information from HA services on each node is used to choose a
+recovery node. Usage of non-HA-managed services is currently not considered.
+
+For this selection, each node in turn is considered as if the service was
+already running on it, using CPU and memory usage from the associated guest
+configuration. Then for each such alternative, CPU and memory usage of all nodes
+are considered, with memory being weighted much more, because it's a truly
+limited resource. For both, CPU and memory, highest usage among nodes (weighted
+more, as ideally no node should be overcommitted) and average usage of all nodes
+(to still be able to distinguish in case there already is a more highly
+committed node) are considered.
+
+IMPORTANT: The more services the more possible combinations there are, so it's
+currently not recommended to use it if you have thousands of HA managed
+services.
+
+
+CRS Scheduling Points
+~~~~~~~~~~~~~~~~~~~~~
+
+The CRS algorithm is not applied for every service in every round, since this
+would mean a large number of constant migrations. Depending on the workload,
+this could put more strain on the cluster than could be avoided by constant
+balancing.
+That's why the {pve} HA manager favors keeping services on their current node.
+
+The CRS is currently used at the following scheduling points:
+
+- Service recovery (always active). When a node with active HA services fails,
+ all its services need to be recovered to other nodes. The CRS algorithm will
+ be used here to balance that recovery over the remaining nodes.
-Service disabled because of LRM errors. Needs manual intervention.
+- HA group config changes (always active). If a node is removed from a group,
+ or its priority is reduced, the HA stack will use the CRS algorithm to find a
+ new target node for the HA services in that group, matching the adapted
+ priority constraints.
+- HA service stopped -> start transtion (opt-in). Requesting that a stopped
+ service should be started is an good opportunity to check for the best suited
+ node as per the CRS algorithm, as moving stopped services is cheaper to do
+ than moving them started, especially if their disk volumes reside on shared
+ storage. You can enable this by setting the **`ha-rebalance-on-start`**
+ CRS option in the datacenter config. You can change that option also in the
+ Web UI, under `Datacenter` -> `Options` -> `Cluster Resource Scheduling`.
ifdef::manvolnum[]
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