Merge pull request #307482 from MicrosoftDocs/main

Auto Publish – main to live - 2025-10-28 22:00 UTC

Author: learn-build-service-prod[bot]

articles/app-service/configure-zone-redundancy.md

@@ -62,7 +62,7 @@ resource appServicePlan 'Microsoft.Web/serverfarms@2024-11-01' = {
 ## Set zone redundancy for an existing App Service plan
 
 1. To enable zone redundancy on an existing App Service plan, [check for zone redundancy support](#check-for-zone-redundancy-support-on-an-app-service-plan).
-1. If your App Service plan supports zone redundancy, use the Azure portal, the Azure CLI, or Bicep and Azure Resource Manager to enable or disable it.
+1. **If your App Service plan supports zone redundancy,** use the Azure portal, the Azure CLI, or Bicep and Azure Resource Manager to enable or disable it.
 
     # [Azure portal](#tab/portal)
 
@@ -123,6 +123,8 @@ resource appServicePlan 'Microsoft.Web/serverfarms@2024-11-01' = {
 
     ---
 
+1. **If your App Service plan is on a scale unit that doesn't support zone redundancy,** you can't enable zone redundancy on your plan. Instead, you need to [redeploy your apps to a new plan on a different scale unit](../azure-resource-manager/management/move-limitations/app-service-move-limitations.md).
+ 
 ## Check for zone redundancy support on an App Service plan
 
 To check whether an existing App Service plan supports zone redundancy, do the following steps:

articles/azure-resource-manager/management/move-limitations/app-service-move-limitations.md

@@ -63,6 +63,19 @@ You can't move a free App Service managed certificate. Instead, delete the manag
 
 If your free App Service managed certificate gets created in an unexpected resource group, try moving the app service plan back to its original resource group. Then, recreate the free managed certificate. This change fixes the issue.
 
+## Scale units and zone redundancy
+
+Apps can only move between App Service plans that are in the same scale unit. Zone redundancy is a property of the scale unit where the App Service plan is deployed. If your current App Service plan is in a scale unit that doesn't support zone redundancy, you can't enable zone redundancy on that plan.
+
+When you create a new App Service plan with zone redundancy enabled, it's deployed to a different scale unit than your existing non-zone-redundant plan. Because apps can't move between different scale units, you can't move your app to the zone-redundant plan (and therefore inherit its zone redundancy settings).
+
+If your App Service plan is on a scale unit that doesn't support zone redundancy, you can't enable zone redundancy on your plan. Instead, you need to:
+
+1. Create a new App Service plan in a new resource group. When you create a new App Service plan with zone redundancy enabled in a different resource group, it's deployed to a different scale unit.
+1. Redeploy your apps to the new plan. When you create a new plan that's on a different scale unit, you need to redeploy your apps. You can't move apps between plans that are on different scale units.
+
+For more information about zone redundancy requirements and scale units, see [Reliability in Azure App Service](/azure/reliability/reliability-app-service#availability-zone-support).
+
 ## Move support
 
 To determine which App Service resources you can move, see move support status for: