Azure Virtual Desktop Hybrid extension fails with InvalidTemplate on Arc-enabled Firestorm2

Question

Azure Virtual Desktop Hybrid extension fails with InvalidTemplate on Arc-enabled Firestorm2

Prince Amor 0

I am trying to deploy Azure Virtual Desktop Hybrid to an Azure Arc-enabled on-premises VM.

Arc machine:

Firestorm2

Resource group:

Robocamp

Host pool:

VDI-Hybrid-GPU

Subscription:

2d1e3e16-e035-4b32-8b70-2ea1a6ce117d

Machine status:

Azure Arc Agent Status: Connected
AzureAdJoined: YES
AzureAdPrt: YES
HostNameUpdated: SUCCESS
Device Name: Firestorm2
GPU-P is working and NVIDIA RTX 4500 Ada is visible inside the VM

The Azure Virtual Desktop Hybrid extension deployment fails before the extension reaches the machine.

Failed deployment:

Firestorm2-SHProxy

Error:

DeploymentFailed / InvalidTemplate

Exact error:

Deployment template validation failed:

"The template resource '[concat(parameters('vmName'), '/AzureVirtualDesktop')]' at line '1' and column '2338' is not valid. The type property cannot be an expression."

No local extension logs are created under:

C:\ProgramData\GuestConfig\extension_logs\Microsoft.AzureVirtualDesktop.CloudDeviceExtension

This appears to fail during Azure ARM template validation before guest extension execution.

Anusree Nashetty 6,715 Reputation points Microsoft External Staff Moderator

2026-08-01T10:26:30.25+00:00
Hello Prince Amor,

Welcome to the Microsoft Q&A Platform. Thank you for providing the detailed information.

Based on the error DeploymentFailed / InvalidTemplate: "The template resource '[concat(parameters('vmName'), '/AzureVirtualDesktop')]' is not valid. The type property cannot be an expression." the deployment appears to be failing during ARM template validation before the Azure Virtual Desktop extension is delivered to the Azure Arc-enabled machine. This would also explain why no extension logs are present on the machine.

To help narrow down the cause, could you please provide:

Is the deployment being initiated from the Azure portal, Azure CLI, PowerShell, or an ARM/Bicep template?

Is this the first attempt to register this Arc-enabled server with the host pool, or has it worked previously?

Which version of the Azure Connected Machine agent is installed? azcmagent version

Have you successfully deployed other Arc extensions (such as Azure Monitor Agent or Custom Script Extension) to this machine?

Could you share a screenshot of the Deployment Operations details from the failed Firestorm2-SHProxy deployment?

The error suggests the deployment is being rejected during template validation rather than during guest extension installation. The additional details should help identify whether this is a deployment configuration issue or a service-side issue.
Anusree Nashetty 6,715 Reputation points Microsoft External Staff Moderator

2026-08-07T08:04:31.92+00:00

Hello Prince Amor,

I hope you're doing well. Just checking in to see if you had a chance to see my response to your question. Could you please share the requested details.

Thank you.
Anusree Nashetty 6,715 Reputation points Microsoft External Staff Moderator

2026-08-11T14:59:41.1266667+00:00

Hello Prince Amor,

I hope you're doing well. Just checking in to see if you had a chance to see my response to your question. Could you please share the requested details.

Thank you.

1 answer

Your answer

Anusree Nashetty 6,715 Reputation points Microsoft External Staff Moderator

2026-08-01T10:26:30.25+00:00

Hello Prince Amor,

Welcome to the Microsoft Q&A Platform. Thank you for providing the detailed information.

Based on the error DeploymentFailed / InvalidTemplate: "The template resource '[concat(parameters('vmName'), '/AzureVirtualDesktop')]' is not valid. The type property cannot be an expression." the deployment appears to be failing during ARM template validation before the Azure Virtual Desktop extension is delivered to the Azure Arc-enabled machine. This would also explain why no extension logs are present on the machine.

To help narrow down the cause, could you please provide:

Is the deployment being initiated from the Azure portal, Azure CLI, PowerShell, or an ARM/Bicep template?

Is this the first attempt to register this Arc-enabled server with the host pool, or has it worked previously?

Which version of the Azure Connected Machine agent is installed? azcmagent version

Have you successfully deployed other Arc extensions (such as Azure Monitor Agent or Custom Script Extension) to this machine?

Could you share a screenshot of the Deployment Operations details from the failed Firestorm2-SHProxy deployment?

The error suggests the deployment is being rejected during template validation rather than during guest extension installation. The additional details should help identify whether this is a deployment configuration issue or a service-side issue.
Anusree Nashetty 6,715 Reputation points Microsoft External Staff Moderator

2026-08-07T08:04:31.92+00:00

Hello Prince Amor,

I hope you're doing well. Just checking in to see if you had a chance to see my response to your question. Could you please share the requested details.

Thank you.
Anusree Nashetty 6,715 Reputation points Microsoft External Staff Moderator

2026-08-11T14:59:41.1266667+00:00

Hello Prince Amor,

I hope you're doing well. Just checking in to see if you had a chance to see my response to your question. Could you please share the requested details.

Thank you.

Answer 1

Root Cause Analysis

The error DeploymentFailed / InvalidTemplate occurs because the ARM template or Bicep module initiating the extension deployment evaluates the type field using a template function/expression (e.g., [parameters('extensionType')] or [concat(...)]). ARM template engine rules strictly forbid expressions in the resource type field.

Because template validation fails at the Azure Resource Manager (ARM) plane, the deployment aborts before generating a API payload to the guest, explaining why no local execution logs exist under C:\ProgramData\GuestConfig\extension_logs\.

Resolution Steps

Hardcode the Resource Type in the Template Ensure the type property in your deployment template is hardcoded as a literal string rather than an expression.

For Azure Arc-enabled Servers (Hybrid/On-Premises):

JSON

   "type"

  __For Standard Azure VMs:__
  
  JSON
  
  ```yaml
  "type"
  ```
  
  __Fix Resource Naming & Parent Structure__ Separate the parent machine name from the extension name instead of dynamically concatenating them inside `type`:
  
  JSON
  
  ```json
  {

  ```

Deploy via Direct Az CLI / PowerShell Workaround If deploying through the Azure Portal UI or a pre-packaged template triggers this, bypass ARM template processing by issuing a direct Arc extension CLI command: Code snippet
```
   az connectedmachine extension create \
```

--resource-group "Robocamp"
--machine-name "Firestorm2"
--name "AzureVirtualDesktop"
--publisher "Microsoft.AzureVirtualDesktop"
--type "CloudDeviceExtension"
--location "<your-region>"