红帽全球峰会第 31 章 Performing cluster maintenance
In order to perform maintenance on the nodes of your cluster, you may need to stop or move the resources and services running on that cluster. Or you may need to stop the cluster software while leaving the services untouched. Pacemaker provides a variety of methods for performing system maintenance.
- If you need to stop a node in a cluster while continuing to provide the services running on that cluster on another node, you can put the cluster node in standby mode. A node that is in standby mode is no longer able to host resources. Any resource currently active on the node will be moved to another node, or stopped if no other node is eligible to run the resource. For information about standby mode, see Putting a node into standby mode.
If you need to move an individual resource off the node on which it is currently running without stopping that resource, you can use the
pcs resource movecommand to move the resource to a different node. For information about thepcs resource movecommand, see Manually moving cluster resources.When you execute the
pcs resource movecommand, this adds a constraint to the resource to prevent it from running on the node on which it is currently running. When you are ready to move the resource back, you can execute thepcs resource clearor thepcs constraint deletecommand to remove the constraint. This does not necessarily move the resources back to the original node, however, since where the resources can run at that point depends on how you have configured your resources initially. You can relocate a resource to its preferred node with thepcs resource relocate runcommand, as described in Manually moving cluster resources.-
If you need to stop a running resource entirely and prevent the cluster from starting it again, you can use the
pcs resource disablecommand. For information on thepcs resource disablecommand, see Disabling, enabling, and banning cluster resources. -
If you want to prevent Pacemaker from taking any action for a resource (for example, if you want to disable recovery actions while performing maintenance on the resource, or if you need to reload the
/etc/sysconfig/pacemakersettings), use thepcs resource unmanagecommand, as described in Setting a resource to unmanaged mode. Pacemaker Remote connection resources should never be unmanaged. -
If you need to put the cluster in a state where no services will be started or stopped, you can set the
maintenance-modecluster property. Putting the cluster into maintenance mode automatically unmanages all resources. For information about putting the cluster in maintenance mode, see Putting a cluster in maintenance mode. - If you need to update the packages that make up the RHEL High Availability and Resilient Storage Add-Ons, you can update the packages on one node at a time or on the entire cluster as a whole, as summarized in Updating a RHEL high availability cluster.
- If you need to perform maintenance on a Pacemaker remote node, you can remove that node from the cluster by disabling the remote node resource, as described in Upgrading remote nodes and guest nodes.
- If you need to migrate a VM in a RHEL cluster, you will first need to stop the cluster services on the VM to remove the node from the cluster and then start the cluster back up after performing the migration. as described in Migrating VMs in a RHEL cluster.
31.1. Putting a node into standby mode
When a cluster node is in standby mode, the node is no longer able to host resources. Any resources currently active on the node will be moved to another node.
The following command puts the specified node into standby mode. If you specify the --all option, this command puts all nodes into standby mode.
You can use this command when updating a resource’s packages. You can also use this command when testing a configuration, to simulate recovery without actually shutting down a node.
pcs node standby node | --all
The following command removes the specified node from standby mode. After running this command, the specified node is then able to host resources. If you specify the --all option, this command removes all nodes from standby mode.
pcs node unstandby node | --all
Note that when you execute the pcs node standby command, this prevents resources from running on the indicated node. When you execute the pcs node unstandby command, this allows resources to run on the indicated node. This does not necessarily move the resources back to the indicated node; where the resources can run at that point depends on how you have configured your resources initially.
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