Updating Hyper-V Failover Cluster with Cluster-Aware Updating Tool

When you wish to update a failover cluster, I favour the manual process of draining and update each node individually this allows you to catch any issues with the Cluster due to the servers not failover over smoothly.

But there are times when it can be used and should be really as it helps a lot.  The first step is to run the CAU Best Practices Analyzer from within the Cluster-Aware updating Tool with an Administrator account that can admin across all the Nodes of the Cluster.  This will let you know if everything is ready for it to be used.

It should be ran every time there is a change to the nodes that also require Validate a Cluster Wizard to be ran.  it should so be ran if the Nodes updates sources have been changed.

Once everything comes back as ok the following recommendations are also made

1. All other update tools are removed like 3rd part update installers and Windows schedule updates should also be disable.  CAU should be the only tool used for updating on the Nodes and approving updates, this also includes WSUS schedule updating but WSUS can be used as a source
   
   
2. All Nodes must be configured with the same update source
   
   
3.  WSUS must correctly identify the approved updates for the cluster nodes and approve across all Nodes
   
   
4. Sufficient cluster nodes must be online so that the cluster has a quorum and Guest VM can quickly and correctly be drained form a Node with no errors. (If this can not happen it can make CAU fail and get stuck at times)
   
   
5. All cluster nodes must be in the same Active Directory domain and Cluster must be resolvable via DNS
   
   

More Reading 
https://docs.microsoft.com/en-us/windows-server/failover-clustering/cluster-aware-updating