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
[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
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.
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
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:
# Note: use default settings for everything
----
+[thumbnail="gui-ha-manager-add-resource.png"]
+
Above config was generated using the `ha-manager` command line tool:
----
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[]
-A commom requirement is that a resource should run on a specific
+[thumbnail="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:
The `nofailback` options is mostly useful to avoid unwanted resource
-movements during administartion tasks. For example, if you need to
+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.
recovered services move straight back to the fenced node.
-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_package_updates]]
-Package Updates
----------------
-
-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.
-
-
[[ha_manager_fencing]]
Fencing
-------
reliable, it is not independent of the servers hardware, and thus has
a lower reliability than 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.
+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.
-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.
+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.
+
+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.
+
+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]]
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.
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:
+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
+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.
-enable::
-The service will be started by the LRM if not already running.
+Node Maintenance
+----------------
-disable::
+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.
-The service will be stopped by the LRM if running.
-migrate/relocate::
+Shutdown
+~~~~~~~~
-The service will be relocated (live) to another node.
+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.
-remove::
+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.
-The service will be removed from the HA managed resource list. Its
-current state will not be touched.
-start/stop::
+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[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.
+
+
+Manual Resource Movement
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+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.
-`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).
+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