Address reviewer feedback: preserve existing subnet ranges and cleanup

Use reference() function to read existing subnet addressPrefix instead of omitting it.
Remove unused useExistingPrivateDnsZone parameter and update documentation.

Author: Keshava Kandikonda

ARM_Template_Create_WP/azuredeploy.json

@@ -211,32 +211,18 @@
                 "description": "Set to false to skip subnet creation (useful when subnets already exist)"
             }
         },
-        "vnetAddressPrefix": {
-            "type": "string",
-            "defaultValue": "10.0.0.0/16",
-            "metadata": {
-                "description": "Address space for the VNet (e.g., 10.0.0.0/16)"
-            }
-        },
         "subnetAddressForApp": {
             "type": "string",
             "defaultValue": "10.0.0.0/24",
             "metadata": {
-                "description": "Address prefix for the App Service subnet (e.g., 10.0.0.0/24)"
+                "description": "Address prefix for the App Service subnet when creating new subnets (createSubnets=true). When using existing subnets (createSubnets=false), this parameter is ignored and the existing subnet's address range is preserved. Example: 10.0.0.0/24"
             }
         },
         "subnetAddressForDb": {
             "type": "string",
             "defaultValue": "10.0.1.0/24",
             "metadata": {
-                "description": "Address prefix for the Database subnet (e.g., 10.0.1.0/24)"
-            }
-        },
-        "useExistingPrivateDnsZone": {
-            "type": "bool",
-            "defaultValue": false,
-            "metadata": {
-                "description": "Set to true to use an existing Private DNS Zone instead of creating a new one"
+                "description": "Address prefix for the Database subnet when creating new subnets (createSubnets=true). When using existing subnets (createSubnets=false), this parameter is ignored and the existing subnet's address range is preserved. Example: 10.0.1.0/24"
             }
         }
     },
@@ -555,7 +541,7 @@
             "properties": {
                 "addressSpace": {
                     "addressPrefixes": [
-                        "[parameters('vnetAddressPrefix')]"
+                        "[variables('vnetAddress')]"
                     ]
                 },
                 "subnets": []
@@ -569,8 +555,6 @@
             "condition": "[parameters('createSubnets')]",
             "dependsOn": [
             ],
-            "resourceGroup": "[parameters('serverFarmResourceGroup')]",
-            "subscriptionId": "[subscription().subscriptionId]",
             "properties": {
                 "mode": "Incremental",
                 "template": {
@@ -625,8 +609,6 @@
             "condition": "[and(parameters('useExistingVnet'), not(parameters('createSubnets')))]",
             "dependsOn": [
             ],
-            "resourceGroup": "[parameters('serverFarmResourceGroup')]",
-            "subscriptionId": "[subscription().subscriptionId]",
             "properties": {
                 "mode": "Incremental",
                 "template": {
@@ -640,7 +622,7 @@
                             "apiVersion": "2021-03-01",
                             "name": "[format('{0}/{1}', parameters('vnetName'), parameters('subnetForApp'))]",
                             "properties": {
-                                "addressPrefix": "[parameters('subnetAddressForApp')]",
+                                "addressPrefix": "[reference(resourceId(parameters('serverFarmResourceGroup'), 'Microsoft.Network/virtualNetworks/subnets', parameters('vnetName'), parameters('subnetForApp')), '2021-03-01').addressPrefix]",
                                 "delegations": [
                                     {
                                         "name": "dlg-appService",
@@ -656,7 +638,7 @@
                             "apiVersion": "2021-03-01",
                             "name": "[format('{0}/{1}',parameters('vnetName'), parameters('subnetForDb'))]",
                             "properties": {
-                                "addressPrefix": "[parameters('subnetAddressForDb')]",
+                                "addressPrefix": "[reference(resourceId(parameters('serverFarmResourceGroup'), 'Microsoft.Network/virtualNetworks/subnets', parameters('vnetName'), parameters('subnetForDb')), '2021-03-01').addressPrefix]",
                                 "delegations": [
                                     {
                                         "name": "dlg-mysql",
@@ -1163,6 +1145,7 @@
         "databaseVersion": "8.0.21",
         "vnetDeploymentApiVersion": "2020-07-01",
         "privateDnsApiVersion": "2018-09-01",
+        "vnetAddress": "10.0.0.0/23",
         "blobApiVersion": "2021-08-01",
         "storageAccountId": "[resourceId(parameters('storageAccountResourceGroup'),'Microsoft.Storage/storageAccounts', parameters('storageAccountName'))]",
         "emailApiVersion": "2023-03-31",

ARM_Template_Create_WP/azuredeploy.parameters.json

@@ -203,17 +203,11 @@
         "createSubnets": {
             "value": true
         },
-        "vnetAddressPrefix": {
-            "value": "10.0.0.0/16"
-        },
         "subnetAddressForApp": {
             "value": "10.0.0.0/24"
         },
         "subnetAddressForDb": {
             "value": "10.0.1.0/24"
-        },
-        "useExistingPrivateDnsZone": {
-            "value": false
         }
     }
 }