The current environment is Windows Server 2016 and SQL Server 2016, with a two-node Always On availability group configured. We have now upgraded the secondary node’s OS to Windows Server 2022. What will be the impact?
Since you’re running SQL Server 2016 on a two-node Always On Availability Group setup, and you’ve upgraded the secondary node’s OS from Windows Server 2016 to Windows Server 2022, here are the potential effects and considerations:
✅ What Will Work (Generally Safe)
- Always On AG Will Still Function:
- SQL Server 2016 is supported on Windows Server 2022 (with some caveats).
- Mixed OS in an AG (Windows Server 2016 + Windows Server 2022) is technically allowed temporarily during upgrades.
- No Immediate Failover Issues:
- As long as the AG health is fine and the upgraded node has the same SQL Server 2016 version and patch level, the AG will continue functioning.
- SQL Server uses the Windows Failover Cluster (WSFC) as its base, and mixed-OS WSFCs are supported during rolling upgrades.
⚠️ Things to Watch Out For
- Windows Cluster Compatibility:
- Mixed-mode clusters (Windows Server 2016 + 2022) are only supported during upgrade and not intended to be permanent.
- Microsoft recommends keeping all nodes on the same OS version for long-term stability and supportability.
- SQL Server 2016 is in Extended Support:
- Some new Windows Server 2022 features (like TLS 1.3 or new network stack behavior) may not fully align with SQL Server 2016’s older behavior. Monitor closely.
- Failover Testing Required:
- Before relying on the upgraded secondary, manually fail over to it and test all application connectivity, agent jobs, linked servers, etc.
- Drivers and Agent Jobs:
- If you have integration components (SSIS, OLEDB drivers, etc.) or any SQL Agent jobs that are OS-specific, validate them on Windows 2022.
- Cluster Validation Tests May Warn:
- If you run
Test-Cluster, it might throw warnings due to OS version mismatch. These are expected but still worth reviewing.
- If you run
✅ Recommended Next Steps
- ✅ Patch SQL Server: Ensure SQL Server 2016 is fully patched (latest CU) on both nodes.
- ✅ Validate AG Health:
- Check
sys.dm_hadr_availability_replica_statesfor sync status. - Monitor dashboards in SSMS.
- Check
- ✅ Plan to Upgrade the Primary Node OS Soon:
- Running a mixed-OS WSFC setup long-term is not supported.
- ✅ Run Failover Tests:
- Simulate failover to the upgraded secondary.
- Validate performance, application response, and logs.
- ✅ Cluster Functional Level:
- Once both nodes are Windows Server 2022, upgrade the cluster functional level (if desired) using:
Update-ClusterFunctionalLevel
- Once both nodes are Windows Server 2022, upgrade the cluster functional level (if desired) using:
Action Items
- Validate AG health with
SELECT * FROM sys.dm_hadr_availability_group_states - Check synchronization status with
SELECT * FROM sys.dm_hadr_database_replica_states - Monitor Windows Cluster logs for any warnings
- Consider running performance benchmarks on both nodes
🔄 Summary
| Component | Status |
|---|---|
| Mixed OS in Always On | ✅ Temporarily supported |
| SQL Server 2016 on Windows 2022 | ✅ Supported |
| Long-term mixed OS cluster | ❌ Not recommended |
| Failover safety | ⚠️ Test before production switch |
| Need to patch SQL | ✅ Strongly recommended |
If you want, I can help you with PowerShell scripts or queries to test your AG health, node readiness, or assist with upgrading the primary. Just say the word!
