mgmt, fix vmss outdated vm (Azure#33444)

* don't fill osDisk for ephemeral VMSS

* fix vmss with ephemeral os disk out-of-date vm issue

Author: XiaofeiCao

sdk/resourcemanager/azure-resourcemanager-compute/CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Bugs Fixed
 
 - Fixed wrong javadocs of `withSsh()` in `VirtualMachine` and `VirtualMachineScaleSet`.
+- Fixed a bug that scaling up scale sets results in outdated models for existing VMs.
 
 ## 2.23.0 (2023-01-27)
 

sdk/resourcemanager/azure-resourcemanager-compute/src/main/java/com/azure/resourcemanager/compute/implementation/VMSSPatchPayload.java

@@ -19,6 +19,10 @@
 import java.util.ArrayList;
 
 class VMSSPatchPayload {
+    /*
+     * Note: innerModel().virtualMachineProfile().storageProfile().osDisk() won't be set if the scale set has ephemeral OS disk.
+     * This may change if backend service decides that ephemeral osDisk can be updated.
+     */
     static VirtualMachineScaleSetUpdate preparePatchPayload(VirtualMachineScaleSet scaleSet) {
         VirtualMachineScaleSetUpdate updateParameter = new VirtualMachineScaleSetUpdate();
         //
@@ -49,7 +53,14 @@ static VirtualMachineScaleSetUpdate preparePatchPayload(VirtualMachineScaleSet s
                     .withImageReference(
                         scaleSet.innerModel().virtualMachineProfile().storageProfile().imageReference());
 
-                if (scaleSet.innerModel().virtualMachineProfile().storageProfile().osDisk() != null) {
+                if (scaleSet.innerModel().virtualMachineProfile().storageProfile().osDisk() != null
+                    // Filling patch payload with osDisk property for VMSS with ephemeral OS disks will be considered updating VM model.
+                    // This may have impact if user want to update the scale set without leaving existing VMs outdated,
+                    // e.g. scale out using `withCapacity`, especially if the scale set's `updatePolicy` is `Rolling` or `Automatic`, which may trigger
+                    // a VM restart.
+                    // Thus, we won't fill for VMSS with ephemeral OS disks.
+                    && !scaleSet.isEphemeralOSDisk()
+                ) {
                     VirtualMachineScaleSetUpdateOSDisk osDisk = new VirtualMachineScaleSetUpdateOSDisk();
                     osDisk
                         .withCaching(scaleSet.innerModel().virtualMachineProfile().storageProfile().osDisk().caching());

sdk/resourcemanager/azure-resourcemanager-compute/src/test/java/com/azure/resourcemanager/compute/VirtualMachineScaleSetOperationsTests.java

@@ -1853,13 +1853,36 @@ public void canCreateVMSSWithEphemeralOSDisk() throws Exception {
             .withPopularLinuxImage(KnownLinuxVirtualMachineImage.UBUNTU_SERVER_18_04_LTS)
             .withRootUsername("jvuser")
             .withSsh(sshPublicKey())
-            .withUpgradeMode(UpgradeMode.AUTOMATIC)
+            .withUpgradeMode(UpgradeMode.MANUAL)
             .withEphemeralOSDisk()
             .withPlacement(DiffDiskPlacement.CACHE_DISK)
-            .withCapacity(2)
+            .withCapacity(1)
             .create();
         Assertions.assertTrue(uniformVMSS.isEphemeralOSDisk());
 
+        // somehow newly created vmss with ephemeral OS disk has outdated VMs and there's a delay before vmss detects that
+        ResourceManagerUtils.sleep(Duration.ofMinutes(1));
+
+        // update VMs to latest model, create baseline
+        uniformVMSS.virtualMachines().updateInstances(
+            uniformVMSS.virtualMachines()
+                .list()
+                .stream()
+                .map(VirtualMachineScaleSetVM::instanceId)
+                .toArray(String[]::new));
+
+        Assertions.assertTrue(uniformVMSS.virtualMachines().list().stream().allMatch(VirtualMachineScaleSetVM::isLatestScaleSetUpdateApplied));
+
+        // scale up vmss
+        uniformVMSS.update()
+            .withCapacity(2)
+            .apply();
+
+        ResourceManagerUtils.sleep(Duration.ofMinutes(1));
+
+        // verify that scaling up won't result in outdated VMs
+        Assertions.assertTrue(uniformVMSS.virtualMachines().list().stream().allMatch(VirtualMachineScaleSetVM::isLatestScaleSetUpdateApplied));
+
         // flex vmss with ephemeral os disk
         Network network2 =
             this