Upgrade Azure Local OS from 2503 to 2603 of 4 node cluster

Rajneesh kumar - please verify the next intended feature version is offered and approved for the node (via Windows Update / WSUS / WUfB).

1. Drain the node.
2. Run CAU on that single node.
3. Validate OS build/version post-update (winver / Get-ComputerInfo).
4. Repeat the process for the next node and next version hop.

Microsoft refernces-

1. CAU overview: -https://learn.microsoft.com/en-us/windows-server/failover-clustering/cluster-aware-updating
2. Invoke-CauRun https://learn.microsoft.com/en-us/powershell/module/clusterawareupdating/invoke-caurun?view=windowsserver2025-ps
3. How Cluster-Aware Updating plug-ins work https://learn.microsoft.com/en-us/windows-server/failover-clustering/cluster-aware-updating-plug-ins
4. WSUS feature update approvals: https://learn.microsoft.com/windows-server/administration/windows-server-update-services/deploy/3-approve-and-deploy-updates-in-wsus

Invoke-CauRun with -CauPluginName Microsoft.WindowsUpdatePlugin does not let Cluster-Aware Updating explicitly choose a specific intermediate Azure Local OS version (2504, 2509, 2520, etc.). It simply applies whatever updates Windows Update (or your configured update source) offers to that node, according to the configured update policies.

For Azure Local, the supported and documented approach is:

1. Upgrade the OS to the next target Azure Local OS version using the RollingUpgrade CAU plugin (not the WindowsUpdate plugin), following the documented path.
2. After the OS is upgraded across the cluster, perform the post‑OS upgrade steps.
3. Then validate and apply the solution upgrade.

From the documentation, the OS upgrade is driven by Microsoft.RollingUpgradePlugin and, when not using Windows Update directly, by pointing CAU at specific setup media for the desired version:

Invoke-CauRun –ClusterName <SystemName> `
  -CauPluginName Microsoft.RollingUpgradePlugin `
  -EnableFirewallRules `
  -CauPluginArguments @{ 
      'WuConnected'='false';
      'PathToSetupMedia'='\\some\\path\\';
      'UpdateClusterFunctionalLevel'='true'; 
  } `
  -ForceSelfUpdate -Force

or, when using Windows Update for the feature upgrade:

Invoke-CauScan -ClusterName <SystemName> `
  -CauPluginName "Microsoft.RollingUpgradePlugin" `
  -CauPluginArguments @{'WuConnected'='true';} -Verbose | fl *

The Invoke-CauScan output is what shows exactly which feature update (OS version) will be applied to each node. That is the supported way to verify which version is going to be installed before running Invoke-CauRun.

Key points for the scenario:

1. Do not rely on Microsoft.WindowsUpdatePlugin if the goal is to control a specific Azure Local OS upgrade path; use Microsoft.RollingUpgradePlugin as documented.
2. To see which OS version will be installed next, run Invoke-CauScan with the RollingUpgrade plugin and inspect the offered feature update for each node.
3. For offline/ISO-based upgrades, control the exact version by using the PathToSetupMedia argument pointing to the extracted ISO contents of the desired Azure Local OS build.
4. After the OS upgrade path is completed to 2603, run the post‑OS upgrade steps (cluster functional level, storage pool update, etc.) before applying the solution upgrade.

Screenshots for the exact path 2503 → 2504 → 2509 → 2520 → 2603 are not provided in the documentation; the supported mechanism is the same RollingUpgrade CAU flow for each step, with the appropriate media or update source.

References:

• Upgrade Azure Stack HCI OS via PowerShell (os-23h2)
• Upgrade Azure Stack HCI OS via PowerShell (os-24h2)
• About Azure Local upgrades
• Perform post operating system upgrade steps on Azure Local via PowerShell