title: Applying custom image to an existing azure scaleset which was created using custom image
body: <p>I have created an azure scaleset using custom image. when I try to upgrade the scale set with another custom image using "Azure VMSS: update with immutable machine image" I get the following error</p>
  
  <blockquote>
    <p>Failed to update image for VMSS testvmssapp. Error: VMSS testvmssapp
    can not be updated as it uses a platform image. Only a VMSS which is
    currently using a custom image can be updated.</p>
  </blockquote>
  
  <p>Is there something I am missing with custom scaleset image?</p>
  
  <pre><code>"storageProfile": {
              "osDisk": {
                "createOption": "FromImage",
                "caching": "ReadWrite",
                "managedDisk": {
                  "storageAccountType": "Standard_LRS"
                },
                "diskSizeGB": 127
              },
              "imageReference": {
                "id": "/subscriptions/xxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxx/resourceGroups/testvmssdeployment/providers/Microsoft.Compute/images/MyCustomImage"
              }
            },
  </code></pre>
  
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