Arc Resource Bridge VM is missing

Hello @Robin,

Thank you for providing the detailed information — this is very helpful.

From your description, the Arc Resource Bridge VM is missing from Hyper‑V while the Azure resource still exists, which is why you’re seeing ResourceBridge status = Offline and management operations being blocked.

What’s happening

The Arc Resource Bridge (ARB) is a critical component for Azure Arc–enabled environments (including AKS on Azure Local). If the underlying VM is deleted or becomes unavailable:

• Azure still shows the appliance resource as existing
• However, the actual connectivity layer is broken, resulting in:
  • ResourceBridge = Offline
  • Blocked VM / AKS management from Azure
  • Cluster updates failing

Recommended resolution

Based on Microsoft guidance for Arc appliances, the supported approach in this scenario is to re-create or repair the Arc Resource Bridge, since the VM backing the appliance is no longer present.

1. Validate current state

• Confirm via:
  • az arcappliance show
    • Hyper‑V: Get-VM (already validated in your case)

2. Restart / redeploy the Arc Resource Bridge (preferred fix)

If the VM is fully missing, it cannot be recovered — you will need to redeploy the appliance:

• Re-run the Arc Resource Bridge deployment/repair process
• Use the same configuration (network, cluster, region)

3. Clean up stale/orphaned resources (important in your case)

Since you mentioned:

• orphaned MOC disk registrations
• VHDX locks preventing cleanup

These usually occur when the appliance VM is removed unexpectedly. You may need to:

• Remove stale MOC entries via PowerShell
• Ensure no storage locks remain before redeployment

(This step ensures the new ARB deployment succeeds without conflicts.)

4. Reconnect AKS / cluster resources

Once ARB is redeployed:

• Azure connectivity will be restored
• AKS clusters should become manageable again through the portal

Microsoft documentation

For reference, please review:

1. https://learn.microsoft.com/azure/azure-arc/resource-bridge/overview
2. https://learn.microsoft.com/azure/azure-arc/resource-bridge/troubleshoot

Summary

In this case, the issue is not with Azure itself but with the missing on‑premises Arc Resource Bridge VM, which is essential for connectivity. Since the VM no longer exists, the recommended resolution is to redeploy the Arc Resource Bridge and clean up any orphaned artifacts beforehand.

Hello Robin Lee,

Greetings! Thanks for raising this question in Q&A forum.

I can understand how critical and urgent this situation is — a missing Arc Resource Bridge (ARB) VM with blocked cluster updates, two unmanageable AKS clusters, and ~5.5TB of orphaned MOC disk locks is a serious production-impacting issue. Let me explain what's happening and the safest path forward.

The Arc Resource Bridge is a critical infrastructure component of Azure Local. It acts as the backbone for all Arc-enabled VM management and AKS operations on your cluster. When the ARB VM disappears from Hyper-V but the Azure arcappliance resource still exists in Azure, you end up in a split-brain state — Azure thinks the bridge is there, but on-premises it's gone. This is exactly why your cluster update is failing at the UpdateArbAndExtensions step with ResourceBridge Status = Offline, and why all Arc VM and AKS management operations are blocked.

Here is the right course of action:

Step 1: Do NOT attempt to manually delete or rebuild the Arc Resource Bridge

This is very important. For Azure Local, Microsoft explicitly documents that the Arc Resource Bridge must not be deleted, manually recreated, or recovered using generic Arc recovery scripts (such as those for Arc VMware or SCVMM). Doing so can cause backend inconsistencies that could lead to an irrecoverable state for your Azure Local environment. Please avoid any further PowerShell-based attempts on the ARB or the arcappliance resource until Microsoft Support is involved.

Step 2: Open a Microsoft Support Case Immediately

This scenario — missing ARB VM on-premises with the Azure resource still present — requires a Microsoft Support–guided recovery. Open a Priority support case at https://aka.ms/azuresupport and select Azure Local as the product area.

Step 3: Provide These Details in Your Support Ticket

To help the support team act quickly, include the following information in your ticket:

• Azure Local cluster version: 12.2602.1002.7
• Region: West Europe
• Cluster update version attempted: 12.2603.1002.500
• Update failure step: UpdateArbAndExtensions
• Arc Resource Bridge status: Offline
• Get-VM on all three nodes returns no ARB VM
• az arcappliance show confirms the Azure resource still exists
• Two AKS clusters running but unmanageable from Azure Portal
• Approximately 5.5TB of orphaned MOC disk registrations holding VHDX file locks preventing storage pool cleanup

Step 4: What Microsoft Support Will Help You Do

The support team will guide you through a safe, supported recovery process that includes recreating or restoring the Arc Resource Bridge VM in a way that reconciles it with the existing Azure arcappliance resource, unblocking the cluster update at the UpdateArbAndExtensions step, restoring AKS cluster management via the Azure Portal, and safely releasing the orphaned MOC disk registrations and VHDX file locks as part of the guided cleanup. These steps must be done in a specific sequence by the support team to avoid further damage to your environment.

If this answer helps you kindly accept the answer which will help others who have similar questions.

Best Regards,

Jerald Felix.