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.
How It Works
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[]
+[thumbnail="gui-ha-manager-add-group.png"]
+
A commom 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:
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
-------
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.
+
+We thus wanted to integrate a simpler fencing method, which does not
+require additional external hardware. This can be done using
+watchdog timers.
-Those are often quite expensive and bring additional critical components in
-a system, because if they fail you cannot recover any service.
+.Possible Fencing Methods
+- external power switches
+- isolate nodes by disabling complete network traffic on the switch
+- self fencing using watchdog timers
-We thus wanted to integrate a simpler method in the HA Manager first, namely
-self fencing with watchdogs.
+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.
-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.
+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.
+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 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.
-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.
+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:
-* bring the resource back into a safe and consistent state (e.g.,
-killing its process)
+----
+# ha-manager set vm:100 --state disabled
+----
+
+This can also be done in the web interface.
-* disable the ha resource to place it in an stopped state
+To recover from the error state you should do the following:
+
+* bring the resource back into a safe and consistent state (e.g.:
+kill its process if the service could not be stopped)
+
+* 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_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.
+
+
+Node Maintenance
+----------------
+
+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.
+
+
+Shutdown
+~~~~~~~~
+
+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.
+
+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.
+
+
+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.
+
+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.
[[ha_manager_service_operations]]
This are how the basic user-initiated service operations (via
`ha-manager`) work.
-enable::
+set state::
-The service will be started by the LRM if not already running.
+Request the service state.
+See xref:ha_manager_resource_config[Resource Configuration] for possible
+request states.
++
+----
+# ha-manager set SID -state REQUEST_STATE
+----
disable::
-The service will be stopped by the LRM if running.
+The service will be placed in the stopped state, even if it was in the error
+state. The service will not be recovered on a node failure and will stay
+stopped while it is in this state.
migrate/relocate::
projects / pve-docs.git / blobdiff