Cluster-Aware Updating: Frequently Asked Questions


Applies To: Windows Server 2012 R2, Windows Server 2012

Cluster-Aware Updating (CAU) is a feature that coordinates software updates on all servers in a failover cluster in a way that does not impact the service availability any more than a planned failover of a cluster node. For some applications with continuous availability features (such as Hyper-V with live migration, or an SMB 3.0 file server with SMB Transparent Failover), CAU can coordinate automated cluster updating with no impact on service availability.

For common questions about Cluster-Aware Updating in Windows Server 2016, see Cluster-Aware Updating: Frequently Asked Questions.

Does CAU work with Windows Server 2008 R2 or Windows 7?

No. CAU coordinates the cluster updating operation only from computers running the Windows Server 2012 R2, Windows Server 2012, Windows 8.1 or Windows 8 operating system.

Is CAU functionality limited to only specific clustered applications?

No. CAU is agnostic to the type of the clustered application. CAU is an external cluster-updating solution that is layered on top of clustering APIs and Windows PowerShell cmdlets. As such, CAU can coordinate updating for any clustered application that is configured in a Windows Server 2012 R2 or Windows Server 2012 failover cluster.


Currently, the following Windows Server 2012 clustered workloads are tested and certified for CAU: SMB, Hyper-V, DFS Replication, DFS Namespaces, iSCSI, and NFS.

Does CAU support updates from Microsoft Update and Windows Update?

Yes. By default, CAU is configured with a plug-in that uses the Windows Update Agent (WUA) utility APIs on the cluster nodes. The WUA infrastructure can be configured to point to Microsoft Update and Windows Update or to Windows Server Update Services (WSUS) as its source of updates.

Does CAU support WSUS updates?

Yes. By default, CAU is configured with a plug-in that uses the Windows Update Agent (WUA) utility APIs on the cluster nodes. The WUA infrastructure can be configured to point to Microsoft Update and Windows Update or to Windows Server Update Services (WSUS) as its source of updates.

Can CAU apply limited distribution release updates?

Yes. Limited distribution release (LDR) updates, also called hotfixes, are not published through Microsoft Update or Windows Update, so they cannot be downloaded by the Windows Update Agent (WUA) plug-in that CAU uses by default.

However, CAU includes a second plug-in that you can select to apply hotfix updates. This hotfix plug-in can also be customized to apply non-Microsoft driver, firmware, and BIOS updates.

Can I use CAU to apply cumulative updates?

Yes. If the cumulative updates are general distribution release updates or LDR updates, CAU can apply them.

Can I schedule CAU to apply updates?

Yes. CAU supports the following updating modes, both of which allow updates to be scheduled:

Self-updating Enables the cluster to update itself according to a defined profile and a regular schedule, such as during a monthly maintenance window. You can also start a Self-Updating Run on demand at any time. To enable self-updating mode, you must add the CAU clustered role to the cluster. The CAU self-updating feature performs like any other clustered workload, and it can work seamlessly with the planned and unplanned failovers of an update coordinator computer.

Remote-updating Enables you to start an Updating Run at any time from a computer running Windows Server 2012 R2, Windows Server 2012, Windows 8.1 or Windows 8. You can start an Updating run through the UI or by using the Invoke-CauRunWindows PowerShell cmdlet. Remote-updating is the default updating mode for CAU. You can use Task Scheduler to run the Invoke-CauRun cmdlet on a desired schedule from a remote computer that is not one of the cluster nodes.

Can CAU updates be scheduled when a backup is in progress?

Yes. CAU does not impose any constraints in this regard. However, performing software updates on a server (with the associated potential restarts) while a server backup is in progress is not an IT best practice. Be aware that CAU relies only on clustering APIs to determine resource failovers and failbacks; thus, CAU is unaware of the server backup status.

Can CAU work well with System Center Configuration Manager?

We recommend that you not use both CAU and System Center Configuration Manager to update cluster nodes. CAU coordinates software updates on each cluster node as part of a broader orchestration with a design objective of maintaining service up time through updating cycles. Configuration Manager is also technically capable of updating the cluster nodes. You may use either tool at your discretion. However, be careful to avoid overlapping coverage that might affect availability of your clustered services as a result of each update management tool operating independent of the other.

Do I need administrative credentials to run CAU?

Yes. For running the CAU tools, CAU needs administrative credentials on the local server, or it needs the Impersonate a Client after Authentication user right on the local server or the client computer on which it is running. However, to coordinate software updates on the cluster nodes, CAU requires cluster administrative credentials on every node. Although the CAU UI will start without the credentials, it prompts for the cluster administrative credentials when it connects to a cluster instance to preview or apply updates.

Can I script CAU functionality to automate it further?

Yes. CAU comes with Windows PowerShell cmdlets that offer a rich set of scripting options. These are the same cmdlets that the CAU UI calls to perform CAU actions.

When CAU coordinates updates, what happens to the clustered roles that are active on each cluster node?

Clustered roles (formerly called applications and services) that are active on a node, fail over to other nodes before software updating can commence. CAU orchestrates these failovers by using the failover cluster node maintenance mode, which pauses and drains the node of all active clustered roles. When the software updates are complete, CAU resumes the node and ensures that the clustered roles fail back to the updated node. This in turn enables the distribution of clustered roles relative to nodes to stay the same across the CAU Updating Runs of a cluster.

How does CAU select the target nodes that each clustered role should fail over to?

CAU relies on clustering APIs to coordinate the failovers. The clustering API implementation selects the target nodes by relying on internal metrics and intelligent placement heuristics (such as workload levels) across the target nodes.

Does CAU load balance the clustered roles at the end of the updating process?

CAU does not load balance the clustered nodes, but it attempts to preserve the distribution of clustered roles. When CAU finishes updating a cluster node, it attempts to fail back previously hosted clustered roles to that node. CAU relies on clustering APIs to fail back the resources to the beginning of the pause process. Thus in the absence of unplanned failovers and preferred owner settings, the distribution of clustered roles should remain unchanged.

How does CAU select the order of nodes to update?

By default, CAU selects the order of nodes to update based on the level of activity. The nodes that are hosting the fewest clustered roles are updated first. However, an administrator can specify a particular order for updating the nodes by specifying a parameter for the Updating Run in the CAU UI or by using the Windows PowerShell cmdlets.

When a CAU Updating Run is initiated on the cluster, what happens if all the cluster nodes are not online?

The administrator who initiates an Updating Run can specify the acceptable threshold for the number of nodes that can be offline. Therefore, an Updating Run can proceed on a cluster even if all the cluster nodes are not online.

Can I use CAU to select and update only a single node?

No. CAU is a cluster-scoped updating tool, so it only allows you to select clusters to update. If you want to update a single node, you can use existing server updating tools independently of CAU.

Can CAU report cluster node updates that are initiated from outside CAU?

No. CAU can only report Updating Runs that are initiated from within CAU. However, when a subsequent CAU Updating Run is launched, updates that were installed through non-CAU methods are appropriately considered to determine the additional updates that might be applicable to each cluster node.

Is CAU flexible enough to support my unique IT process needs?

Yes. CAU offers the following dimensions of flexibility to suit enterprise customers' unique IT process needs:

Scripts An Updating Run can specify a pre-update Windows PowerShell script and a post-update Windows PowerShell script. The pre-update script runs on each cluster node before the node is paused. The post-update script runs on each cluster node after the node updates are installed.


.NET Framework 4.5 and Windows PowerShell must be installed on each cluster node on which you want to run the pre-update and post-update scripts. You must also enable Windows PowerShell remoting on the cluster nodes. For detailed system requirements, see CAU: Requirements and Best Practices.

Advanced Updating Run options The administrator can additionally specify from a large set of advanced Updating Run options such as the maximum number of times that the update process will be retried on each node. These options can be specified using either the CAU UI or the CAU Windows PowerShell cmdlets. These custom settings can be saved in an Updating Run Profile and reused for later Updating Runs.

Public plug-in architecture CAU includes features to Register, Unregister, and Select plug-ins. CAU ships with two default plug-ins: one coordinates the Windows Update Agent (WUA) APIs on each cluster node; the second applies hotfixes that are manually copied to a file share that is accessible to the cluster nodes. If an enterprise has unique needs that cannot be met with these two plug-ins, the enterprise can build a new CAU plug-in according to the public API specification. For more information, see Cluster-Aware Updating Plug-in Reference.

For information about configuring and customizing CAU plug-ins to support different updating scenarios, see CAU: How Plug-ins Work.

How can I export the CAU preview and update results?

CAU offers export options through the command-line interface and through the UI.

Command-line interface options:

  • Preview results by using the Windows PowerShell cmdlet Invoke-CauScan | ConvertTo-Xml. Output: XML

  • Report results by using the Windows PowerShell cmdlet Invoke-CauRun | ConvertTo-Xml. Output: XML

  • Report results by using the Windows PowerShell cmdlet Get-CauReport | Export-CauReport. Output: HTML, CSV

UI options:

  • Copy the report results from the Preview updates screen. Output: CSV

  • Copy the report results from the Generate report screen. Output: CSV

  • Export the report results from the Generate report screen. Output: HTML

How do I install CAU?

CAU is included with all Windows Server 2012 R2 and Windows Server 2012 editions. A CAU installation is seamlessly integrated into the Failover Clustering feature. CAU is installed as follows:

  • When Failover Clustering is installed on a cluster node, the CAU Windows Management Instrumentation (WMI) provider is automatically installed.

  • When Failover Clustering tools are installed on a server or client computer, the CAU Windows PowerShell cmdlets are automatically installed.

  • When the Failover Clustering UI is installed on a server or client computer, the CAU Windows PowerShell cmdlets and the CAU UI are automatically installed.

Does CAU need any service or component running on the cluster nodes that are being updated?

CAU does not need a service running on the cluster nodes. However, CAU needs a software component (the WMI provider) installed on the cluster nodes. This component is installed with the Failover Clustering feature.

To enable self-updating mode, the CAU clustered role must also be added to the cluster.

What is the difference between using CAU and using System Center 2012 Virtual Machine Manager to update Hyper-V clusters?

  • System Center 2012 Virtual Machine Manager (VMM) is focused on updating only Hyper-V clusters, whereas CAU can update any type of supported failover cluster, including Hyper-V clusters.

  • VMM requires additional licensing, whereas CAU is licensed for all Windows Server 2012 R2 and Windows Server 2012 editions. The CAU features, tools, and UI are installed with Failover Clustering components.

  • If you already own a System Center license, you can continue to use VMM to update Hyper-V clusters because it offers an integrated management and software updating experience.

  • CAU is supported only on clusters that are running Windows Server 2012 R2 and Windows Server 2012. VMM also supports Hyper-V clusters on computers running Windows Server 2008 and Windows Server 2008 R2.

Can I use remote-updating on a cluster that is configured for self-updating?

Yes. A failover cluster in a self-updating configuration can be updated through remote-updating on-demand, just as you can force a Windows Update scan at any time on your computer, even if Windows Update is configured to install updates automatically. However, you need to make sure that an Updating Run is not already in progress.

Can I reuse my cluster update settings across clusters?

Yes. CAU supports a number of Updating Run options that determine how the Updating Run behaves when it updates the cluster. These options can be saved as an Updating Run Profile, and they can be reused across any cluster. We recommend that you save and reuse your settings across failover clusters that have similar updating needs. For example, you might create a “Business-Critical SQL Server Cluster Updating Run Profile” for all Microsoft SQL Server clusters that support business-critical services.

Where can I get more information about the public CAU plug-in specification?

See also