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.
+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 keeps it
+running. Please note that you can configure the ``requested''
+resources state. For example you may want that the HA stack stops 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`. Same applied 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. So 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 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 task can be done on 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`::
[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
+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
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
lock.
+
+Service States
+~~~~~~~~~~~~~~
+
+The CRM use a service state enumeration to record the current service
+state. We display this state on the GUI and you can query it 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 (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
+(see xref:ha_manager_fencing[Fencing]).
+
+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]).
+
+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`
+
+
Local 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.
+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 which 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
the same HA configuration.
+[[ha_manager_resource_config]]
Resources
~~~~~~~~~
+[thumbnail="gui-ha-manager-status.png"]
+
+
The resource configuration file `/etc/pve/ha/resources.cfg` stores
the list of resources managed by `ha-manager`. A resource configuration
inside that list look like this:
----
-<sid>:
+<type>: <name>
<property> <value>
...
----
-It starts with the service ID followed by a collon. The next lines
-contain additional properties:
+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 posiible 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="gui-ha-manager-add-resource.png"]
+
+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="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
include::ha-groups-opts.adoc[]
+[thumbnail="gui-ha-manager-add-group.png"]
-Node Power Status
------------------
+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:
-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 groupadd prefer_node1 --nodes node1
+----
-Package Updates
----------------
+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 splitted 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:
-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.
+----
+# 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
+----
+
+Above commands created the following group configuration fils:
+
+.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
+----
-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 `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 hasn't the highest priority in the
+group, you need to tell the HA manager to not move this service
+instantly 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 failure cause and check if it runs
+stable again. Setting the `nofailback` flag prevents that the
+recovered services move 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, it would not be possible to
+recover a resource on another node.
+
+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 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 conditions because we write from both nodes. Such
+condition can destroy all VM data and the whole VM could be rendered
+unusable. The recovery could also fail if the storage protects from
+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 are widely used in critical and dependable systems
+since the beginning of micro controllers. They are often independent
+and simple 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 triggers 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 load
+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.
-
-[[ha_manager_groups]]
-Groups
-------
+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.
-A group is a collection of cluster nodes which a service may be bound to.
+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.
-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 increase 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
---------------------
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:
-
-* bring the resource back into a safe and consistent state (e.g.,
-killing its process)
-
-* disable the ha resource to place it in an stopped state
-
-* fix the error which led to this failures
-
-* *after* you fixed all errors you may enable the service again
-
-
-[[ha_manager_service_operations]]
-Service Operations
-------------------
-
-This are how the basic user-initiated service operations (via
-`ha-manager`) work.
+by the HA stack anymore. The only way out is disabling a service:
-enable::
+----
+# ha-manager set vm:100 --state disabled
+----
-The service will be started by the LRM if not already running.
+This can also be done in the web interface.
-disable::
+To recover from the error state you should do the following:
-The service will be stopped by the LRM if running.
+* bring the resource back into a safe and consistent state (e.g.:
+kill its process if the service could not be stopped)
-migrate/relocate::
+* disable the resource to remove the error flag
-The service will be relocated (live) to another node.
+* fix the error which led to this failures
-remove::
+* *after* you fixed all errors you may request that the service starts again
-The service will be removed from the HA managed resource list. Its
-current state will not be touched.
-start/stop::
+[[ha_manager_package_updates]]
+Package Updates
+---------------
-`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).
+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.
-Service States
---------------
-stopped::
+Node Maintenance
+----------------
-Service is stopped (confirmed by LRM), if detected running it will get stopped
-again.
+It is sometimes possible to shutdown or reboot a node to do
+maintenance tasks. Either to replace hardware, or simply to install a
+new kernel image.
-request_stop::
-Service should be stopped. Waiting for confirmation from LRM.
+Shutdown
+~~~~~~~~
-started::
+A shutdown ('poweroff') is usually done if the node is planned to stay
+down for some time. The LRM stops all managed services in that
+case. This means that other nodes will take over those service
+afterwards.
-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.
+NOTE: Recent hardware has large amounts of 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.
-fence::
-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.
+Reboot
+~~~~~~
-freeze::
+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.
-Do not touch the service state. We use this state while we reboot a
-node, or when we restart the LRM daemon.
+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[Pakage Updates]). This prevents
+that those resources are moved to other nodes. Instead, the CRM start
+the resources after the reboot on the same node.
-migrate::
-Migrate service (live) to other node.
+Manual Resource Movement
+~~~~~~~~~~~~~~~~~~~~~~~~
-error::
+Last but not least, you can also move resources manually 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.
-Service disabled because of LRM errors. Needs manual intervention.
+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 a node reboot.
ifdef::manvolnum[]
projects / pve-docs.git / blobdiff