Update automatic-vm-guest-patching.md

Updated information on patch modes and apphealth requirement.

Author: maulikshah23

articles/virtual-machines/automatic-vm-guest-patching.md

@@ -146,20 +146,23 @@ VMs on Azure now support the following patch orchestration modes:
 - For Windows VMs, setting this mode also disables the native Automatic Updates on the Windows virtual machine to avoid duplication.
 - To use this mode on Linux VMs, set the property `osProfile.linuxConfiguration.patchSettings.patchMode=AutomaticByPlatform` in the VM template.
 - To use this mode on Windows VMs, set the property  `osProfile.windowsConfiguration.patchSettings.patchMode=AutomaticByPlatform` in the VM template.
+- Enabling this mode will set the SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU\NoAutoUpdate RegKey to 1 
 
 **AutomaticByOS:**
 - This mode is supported only for Windows VMs.
 - This mode enables Automatic Updates on the Windows virtual machine, and patches are installed on the VM through Automatic Updates.
 - This mode does not support availability-first patching.
 - This mode is set by default if no other patch mode is specified for a Windows VM.
 - To use this mode on Windows VMs, set the property `osProfile.windowsConfiguration.enableAutomaticUpdates=true`, and set the property  `osProfile.windowsConfiguration.patchSettings.patchMode=AutomaticByOS` in the VM template.
+- Enabling this mode will set the SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU\NoAutoUpdate RegKey to 0
 
 **Manual:**
 - This mode is supported only for Windows VMs.
 - This mode disables Automatic Updates on the Windows virtual machine. When deploying a VM using CLI or PowerShell, setting `--enable-auto-updates` to `false` will also set `patchMode` to `manual` and will disable Automatic Updates. 
 - This mode does not support availability-first patching.
 - This mode should be set when using custom patching solutions.
 - To use this mode on Windows VMs, set the property `osProfile.windowsConfiguration.enableAutomaticUpdates=false`, and set the property  `osProfile.windowsConfiguration.patchSettings.patchMode=Manual` in the VM template.
+- Enabling this mode will set the SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU\NoAutoUpdate RegKey to 1 
 
 **ImageDefault:**
 - This mode is supported only for Linux VMs.
@@ -180,6 +183,7 @@ VMs on Azure now support the following patch orchestration modes:
 - The virtual machine must be able to access the configured update endpoints. If your virtual machine is configured to use private repositories for Linux or Windows Server Update Services (WSUS) for Windows VMs, the relevant update endpoints must be accessible.
 - Use Compute API version 2021-03-01 or higher to access all functionality including on-demand assessment and on-demand patching.
 - Custom images aren't currently supported.
+- VMSS Flexible Orchestration require the installation of [Application Health extension](../virtual-machine-scale-sets/virtual-machine-scale-sets-health-extension.md). This is optional for IaaS VMs. 
 
 ## Enable automatic VM guest patching
 Automatic VM guest patching can be enabled on any Windows or Linux VM that is created from a supported platform image.  
@@ -274,6 +278,8 @@ When automatic VM guest patching is enabled for a VM, a VM extension of type `Mi
 
 It can take more than three hours to enable automatic VM guest updates on a VM, as the enablement is completed during the VM's off-peak hours. The extension is also installed and updated during off-peak hours for the VM. If the VM's off-peak hours end before enablement can be completed, the enablement process will resume during the next available off-peak time.
 
+Please note that the platform will make periodic patching configuration calls to ensure alignment when model changes are detected on IaaS VMs or VMSS Flexible orchestration. Certain model changes such as, but not limited to, updating assessment mode, patch mode, and extension update may trigger a patching configuration call.
+
 Automatic updates are disabled in most scenarios, and patch installation is done through the extension going forward. The following conditions apply.
 - If a Windows VM previously had Automatic Windows Update turned on through the AutomaticByOS patch mode, then Automatic Windows Update is turned off for the VM when the extension is installed.
 - For Ubuntu VMs, the default automatic updates are disabled automatically when Automatic VM Guest Patching completes enablement.