Hotpatching in Windows Server 2025 allows admins to apply critical updates without restarting the system. Hotpatching is available in the Standard and Datacenter editions of Windows Server 2025. It can be used in on-premises environments, the Azure cloud, or virtual servers with VMware or Hyper-V, provided that Virtualization-Based Security (VBS) is supported.

What is Hotpatching?

Hotpatching updates the in-memory code of running processes, enabling the application of security updates without requiring a restart. Unlike traditional updates, which necessitate restarts because files cannot be replaced while in use, Hotpatching allows system updates while avoiding restarts.

Windows Server 2025 Hotpatching only updates security-relevant components. Hotpatch update packages are smaller, reducing installation times and conserving CPU and storage resources.

Hotpatching offers these advantages:

Minimal downtime: Servers remain operational as no restarts are necessary.

Improved security: Security updates can be applied immediately without waiting for maintenance windows.

Reduced planning time: It simplifies the planning and execution of maintenance tasks.

Hotpatching requirements

The Hotpatching feature is dependent on the following requirements:

Supported editions: Standard or Datacenter editions of Windows Server 2025

Stable internet connection: Essential for accessing Microsoft update servers

Azure Arc integration: Connection to Azure Arc to manage Hotpatch updates

Virtualization-Based Security (VBS): Systems support for VBS

VBS uses hardware virtualization to create an isolated environment that protects critical system processes and sensitive data from unauthorized access or malware.

Enable Hotpatching on Windows Server 2025

Connect to Azure Arc

If your server is not yet connected to Azure Arc, follow these steps:

1. Open Azure Portal: Log in to the Azure portal.
2. Add Azure Arc for Servers: Navigate to Azure Arc > Servers > + Add.
3. Download the installation script: Download the script to connect the server to Azure. Alternatively, use the setup assistant in Windows Server 2025 to connect directly.
4. Run the script: Execute the script on your server to register it with Azure Arc.
5. Test the connection: Verify that your server is visible in the portal under Azure Arc.

Enable Hotpatching

Configure Azure Update Manager

1. Navigate to Overview
2. Select your server

Enable Hotpatching (Preview)

1. Ensure your server has the necessary license.
2. Save the configuration.

Troubleshoot Hotpatching activation

Possible issues include the server not being connected to Azure Arc or VBS not being active. In the first case, ensure an active internet connection and that your Azure account credentials are available.

VBS is supposed to be enabled by default on Windows Server 2025, but this might not always be the case. You can use the systeminfo command to verify if VBS is active.

If VBS is not active, you can turn it on with this Group Policy setting:

Computer Configuration > Administrative Templates > System > Device Guard > Turn On Virtualization Based Security

Verify Hotpatch updates

In Windows Update, you can confirm that Hotpatching is working:

Settings > Windows Update > Update History

You have to look for updates labeled Hotpatch.

Hotpatch update strategy

At the beginning of each calendar quarter—January, April, July, and October—your servers receive a comprehensive monthly security update. This standard update includes the latest security fixes, new features, and enhancements and is completed with a restart.

In the following two months, so-called Hotpatch updates are provided. These contain only security updates, which can be installed without a restart, ensuring your servers remain protected.

At the start of the next quarter, the cycle begins anew.

With this optimized update strategy, the required restarts are decreased from twelve to four annually, complemented by eight scheduled Hotpatch updates yearly.

Conclusion

Hotpatching in Windows Server 2025 streamlines the update process, making it faster, safer, and more user-friendly. This means reduced maintenance effort and enhanced security for administrators and IT professionals. In critical environments where downtime leads to considerable disruptions, Hotpatching offers substantial improvement.