Can we detach VM NIC when there is a zone failure?

Question

Hello Microsoft Azure Community,

When Zone 1 is having disaster and impacting VM 1, is it still possible to detach the NIC from VM 1 and attach it to VM 2 in Zone 2? Can we also automate this process.

Thanks all in advance!

Answer 1

Hi @Andy Lau Pik Hui

Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.

1. If your VM1 in Zone 1 is having only 1 NIC, so it can't be detached. A VM must have at least one network interface attached to it. For your reference: https://learn.microsoft.com/en-us/azure/virtual-network/virtual-network-network-interface-vm#constraints
2. The VM2 in Zone 2 needs to support for multiple NICs, if the size of the VM is not supported, we cannot attach the NIC to the VM2. A VM can only have as many network interfaces attached to it as the VM size supports. Please refer: https://learn.microsoft.com/en-us/azure/virtual-machines/sizes/overview?tabs=breakdownseries%2Cgeneralsizelist%2Ccomputesizelist%2Cmemorysizelist%2Cstoragesizelist%2Cgpusizelist%2Cfpgasizelist%2Chpcsizelist
3. When you delete a VM, the network interfaces are detached from the VM. You can add those network interfaces to different VMs or delete them. For your reference: https://learn.microsoft.com/en-us/azure/virtual-network/virtual-network-network-interface-vm#:~:text=Deleting%20a%20VM%20doesn%27t%20delete%20the%20network%20interfaces%20that%20are%20attached%20to%20it.%20When%20you%20delete%20a%20VM%2C%20the%20network%20interfaces%20are%20detached%20from%20the%20VM.%20You%20can%20add%20those%20network%20interfaces%20to%20different%20VMs%20or%20delete%20them.
4. If in case you need to avoid data loss and downtime, you can configure the ASR(Azure Site Recovery). In the event of a disaster, you can fail over to the replicated VM. For your reference: https://learn.microsoft.com/en-us/azure/site-recovery/azure-to-azure-how-to-enable-replication
5. Yes, you can automate the process of detaching and attaching the NIC using Azure Automation, Azure PowerShell, or Azure CLI. You can create a script that performs the necessary steps to detach the NIC from VM 1 and attach it to VM 2.
   Please verify the below example PowerShell script:

      # Detach the NIC from VM 1
      $nic = Get-AzNetworkInterface -Name "VM1-NIC" -ResourceGroupName "RG1"
      $vm = Get-AzVM -Name "VM1" -ResourceGroupName "RG1"
      Remove-AzVMNetworkInterface -VM $vm -NetworkInterface $nic
      # Attach the NIC to VM 2
      $nic = Get-AzNetworkInterface -Name "VM1-NIC" -ResourceGroupName "RG1"
      $vm = Get-AzVM -Name "VM2" -ResourceGroupName "RG2"
      Add-AzVMNetworkInterface -VM $vm -NetworkInterface $nic
   

   For your reference: https://learn.microsoft.com/en-us/azure/virtual-machines/windows/multiple-nics?toc=%2Fazure%2Fvirtual-network%2Ftoc.json#remove-a-nic-from-an-existing-vm

Kindly let us know if the above helps or you need further assistance on this issue.

Thanks,

Sai Prasanna.