Rolling Cluster upgrade to Windows 2012R2 to Windows 2016 - (SQL Server availability group is a workload)

The cluster has two nodes and the workload is SQL server availability group.

Step 1

1. Drain role on one of the nodes
2. Evict the node from a cluster
3. Upgrade OS to Windows 2016
4. After upgrading successfully, add the node back to the cluster

SQL Listener

During the node 1 upgrade, SQL listener is online and application has no down time.

ClusterFunctionalLevel Verificaton

Open PowerShell , Run 

PS C:\WINDOWS\system32> get-cluster | select clusterfunctionallevel

ClusterFunctionalLevel

----------------------

                     8

you will get ClusterFunctionalLevel 8 ( which is a mixed mode clustering )

Step 2

1. Drain role on the second node
2. Evict the node from a cluster
3. Upgrade the node OS to Windows 2016
4. After upgrading successfully, add the node back to the cluster

Step 3

1. Run validate cluster
2. Check ClusterFunctionalLevel again

Open PowerShell , Run 

PS C:\WINDOWS\system32> get-cluster | select clusterfunctionallevel

ClusterFunctionalLevel

----------------------

                     8

you will get ClusterFunctionalLevel 8 ( which is a mixed mode clustering )

Final Step

PS C:\WINDOWS\system32> Update-ClusterFunctionalLevel

NOTE: after you run this command, you cannot rollback.

if it runs successfully, you will get 

PS C:\WINDOWS\system32> get-cluster | select clusterfunctionallevel

ClusterFunctionalLevel

----------------------

                     9

Summary

1. Windows Server 2016 makes upgrading clusters easy with rolling upgrades
2. Control when your cluster upgrade is complete with the Cluster Functional Level
3. Add and manage your Windows Server 2016 cluster from the up-level (2016) nodes