CAU orchestrates these failovers by using the maintenance mode, which pauses and drains the node of all active clustered roles.
When the software updates are complete, CAU resumes the node and the clustered roles fail back to the updated node.
This ensures that the distribution of clustered roles relative to nodes stays the same across the CAU Updating Runs of a cluster.
CAU relies on clustering APIs to coordinate the failovers.
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. 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 a local Windows Server Update Services (WSUS) server as its source of updates. 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.
The nodes that are hosting the fewest clustered roles are updated first.
Remote-updating is the default updating mode for CAU.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.CAU doesn't 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.Be aware that CAU relies only on clustering APIs to determine resource failovers and failbacks; thus, CAU is unaware of the server backup status.