[AppServices] RestoreAzureWebAppSnapshot fetch the data from Microsoft.Web RP similar to other commands (#26685)

* [AppServices] RestoreAzureWebAppSnapshot fetch the data from Microsoft.Web RP similar to other commands

* Add warning message

* Add change log and fix an issue

* Fix typo in ChangeLog.md file

---------

Co-authored-by: Yabo Hu <[email protected]>

Author: vkarasala

src/Websites/Websites/ChangeLog.md

@@ -18,6 +18,7 @@
         - Additional information about change #1
 -->
 ## Upcoming Release
+* Fixd the source app retrival from Microsoft.Web RP instead of ARM cache for `RestoreAzureWebAppSnapshot`
 * Upgraded nuget package to signed package.
 
 ## Version 3.2.2

src/Websites/Websites/Cmdlets/BackupRestore/RestoreAzureWebAppSnapshot.cs

@@ -51,11 +51,34 @@ public class RestoreAzureWebAppSnapshot : WebAppOptionalSlotBaseCmdlet
         public override void ExecuteCmdlet()
         {
             base.ExecuteCmdlet();
-            var sourceApp = ResourcesClient.GetAppResource(InputObject.Name, InputObject.Slot);
+            var sourceAppLocation = string.Empty;
+            var sourceAppArmResourceId = string.Empty;
+
+            // Try to get the source app location and resource ID from Microsoft.Web RP
+            try
+            {
+                var app = new PSSite(WebsitesClient.GetWebApp(InputObject.ResourceGroupName, InputObject.Name, InputObject.Slot));
+                sourceAppLocation = app.Location;
+                sourceAppArmResourceId = app.Id;
+                WriteDebug($"Fetched the source app location and resource ID from Microsoft.Web RP for {InputObject.Name}, Location = {sourceAppLocation}, Id = {sourceAppArmResourceId}");
+            }
+            catch (Exception ex)
+            {
+                WriteDebug($"Unable to fetch the source app location and resource ID from Microsoft.Web RP. {ex.Message}, An attempt will be made to retrieve the same from ARM cache");
+            }
+
+            // Fall back code to fetch the source app location and resource ID from ARM cache, Useful with disaster recovery scenaior's when Microsoft.Web RP is not accessible
+            if (string.IsNullOrEmpty(sourceAppLocation) || string.IsNullOrEmpty(sourceAppArmResourceId))
+            {
+                var sourceApp = ResourcesClient.GetAppResource(InputObject.Name, InputObject.Slot);
+                sourceAppLocation = sourceApp?.Location;
+                sourceAppArmResourceId = sourceApp?.Id;
+            }
+
             SnapshotRecoverySource source = new SnapshotRecoverySource()
             {
-                Location = sourceApp?.Location,
-                Id = sourceApp?.Id
+                Location = sourceAppLocation,
+                Id = sourceAppArmResourceId
             };
             SnapshotRestoreRequest recoveryReq = new SnapshotRestoreRequest()
             {