Node drain
When a failover cluster node needs to be taken down for maintenance,
the clustered roles hosted on that node first need to be moved to
another node in the cluster. Some examples of the kind of maintenance you might need to perform on a cluster node might be upgrading the hardware on the node or applying a service pack.
In the previous version of Failover Clustering in Windows Server
2008 R2, taking down a node for maintenance was a manual process that
required placing the node into a Paused state and then manually moving
the applications and services running on the node to another node on
the cluster.
However, Failover Clustering in Windows Server 2012 now makes performing maintenance on cluster nodes much easier. A new feature called node drain now lets you automate the moving of clustered roles off from the node scheduled for maintenance onto other nodes running on the cluster.
Draining a node can be done either manually by a single click in the Failover Cluster Manager console (as shown in Figure 4), or you can script it with PowerShell for automation purposes by using the Suspend-ClusterNode cmdlet.
Initiating the node drain process does the following:
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Puts the node into the Paused state to prevent roles hosted on other nodes from being moved to this node
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Sorts the roles on the node according to the priority you’ve
assigned them (assigning priorities to roles is another new feature of
Failover Clustering in Windows Server 2012)
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Moves the roles from the node to other nodes in the cluster in order of priority (VMs are live-migrated to other hosts)
Once the process is completed, the node is down and is ready for maintenance.
Cluster-Aware Updating (CAU) is a new feature of Windows Server 2012 that lets you automatically apply software updates to the host
operating system in clustered servers with little or no downtime. CAU
thus both simplifies update management of cluster nodes and helps
ensure your cluster remains available at all times.
CAU functionality
works seamlessly with your Windows Server Update Services (WSUS)
infrastructure and is installed automatically on each cluster
node. CAU can be managed from any server that has the Failover Cluster
feature installed but does not belong to the cluster whose nodes you
wish to update.
As shown previously in Figure 2, you can use Server Manager to initiate the process of updating a cluster. Selecting the Update Cluster menu item opens the Cluster-Aware Updating dialog box and connects to the cluster you selected in Server Manager:
You can also open the Cluster-Aware Updating dialog box from Failover Cluster Manager.
Clicking the Preview Updates
For This Cluster option opens the Preview Updates dialog box, and
clicking Generate Update Preview List in this dialog box downloads a
list of the updates available for nodes in the cluster:
Closing the Preview Updates dialog box returns you to the Cluster-Aware Updating dialog box where clicking the Apply Updates To This Cluster option starts the Cluster-Aware Updating Wizard:
Once you’ve walked through the steps of this wizard and clicked
Next, the update process begins. The way the whole process works is
like this:
Cluster nodes are scanned to determine which updates they require in the following way:
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Nodes are prioritized according to the number of workloads they have running on them.
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The node with the fewest workloads is then drained to place it into
maintenance mode. This causes the workloads running on the node to be
moved automatically to other active nodes in the cluster .
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The Windows
Update Agent on this node downloads the necessary updates from either
Windows Update or from your WSUS server if you have one deployed in
your environment.
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Once the node has been successfully updated, the node is resumed and becomes an active node in the cluster again.
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The process is then repeated on each remaining node in the cluster in turn, according to priority.
CAU employs an
updating run profile to store the settings for how exceptions are
handled, time boundaries for the update process, and other aspects of
the node updating process. You can configure these settings by clicking
the Create Or Modify Updating Run Profile option in the Cluster-Aware Updating dialog box shown previously. Doing this opens the Updating Run Profile Editor, as shown here:
