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Azure VM: Add/attach the availability set to the existing VM

 Once we've created an Azure VM without an Availability set, later if we want to add it to an availability set there is no obvious option on the Azure portal. We can add an availability set only while creating the VM. 

The problem comes when we try to add always-on on IaaS SQL instance one of the pre-requisite is IaaS VMs should be on an availability set. So to enable Always on existing IaaS VM either we've to re-create the VM or need to create a new one & install the required s/w from scratch. 

To resolve this restriction, we can follow the below steps sequentially and achieve this. 

  • Get the list of attached OS + Data disk of existing VM
  • Get the Network interface details. 
  • Remove the Azure Disk Encryption (ADE) if it's enabled. 
  • Remove the Azure VM (delete it)
  • Now create the new with the same name & with Availability set. 
  • After re-creating the VM change the OS disks & Data disk [ask noted in step-1]. 
  • Start the VM and try to access it. 
  • Once you're able to access it & verify it's working, you can start enabling ADE (if required)

The above-mentioned process is all manual and it will take some time. there is well know PowerShell script to automate this. 

Here is the PowerShell script to add/attach availability set to existing VM.  


 
 # Set variables
    $resourceGroup = "<<your-resource-group>>"
    $vmName = "<<your-vm-name>>"
    $newAvailSetName = "<<your-availability-set-name>>"

# Get the details of the VM to be moved to the Availability Set
    $originalVM = Get-AzVM `
	   -ResourceGroupName $resourceGroup `
	   -Name $vmName

# Create new availability set if it does not exist
    $availSet = Get-AzAvailabilitySet `
	   -ResourceGroupName $resourceGroup `
	   -Name $newAvailSetName `
	   -ErrorAction Ignore
    if (-Not $availSet) {
    $availSet = New-AzAvailabilitySet `
	   -Location $originalVM.Location `
	   -Name $newAvailSetName `
	   -ResourceGroupName $resourceGroup `
	   -PlatformFaultDomainCount 2 `
	   -PlatformUpdateDomainCount 2 `
	   -Sku Aligned
    }
    
# Remove the original VM
    Remove-AzVM -ResourceGroupName $resourceGroup -Name $vmName    

# Create the basic configuration for the replacement VM. 
    $newVM = New-AzVMConfig `
	   -VMName $originalVM.Name `
	   -VMSize $originalVM.HardwareProfile.VmSize `
	   -AvailabilitySetId $availSet.Id
 
# For a Linux VM, change the last parameter from -Windows to -Linux 
    Set-AzVMOSDisk `
	   -VM $newVM -CreateOption Attach `
	   -ManagedDiskId $originalVM.StorageProfile.OsDisk.ManagedDisk.Id `
	   -Name $originalVM.StorageProfile.OsDisk.Name `
	   -Windows

# Add Data Disks
    foreach ($disk in $originalVM.StorageProfile.DataDisks) { 
    Add-AzVMDataDisk -VM $newVM `
	   -Name $disk.Name `
	   -ManagedDiskId $disk.ManagedDisk.Id `
	   -Caching $disk.Caching `
	   -Lun $disk.Lun `
	   -DiskSizeInGB $disk.DiskSizeGB `
	   -CreateOption Attach
    }
    
# Add NIC(s) and keep the same NIC as primary
	foreach ($nic in $originalVM.NetworkProfile.NetworkInterfaces) {	
	if ($nic.Primary -eq "True")
		{
    		Add-AzVMNetworkInterface `
       		-VM $newVM `
       		-Id $nic.Id -Primary
       		}
       	else
       		{
       		  Add-AzVMNetworkInterface `
      		  -VM $newVM `
      	 	  -Id $nic.Id 
                }
  	}

# Recreate the VM
    New-AzVM `
	   -ResourceGroupName $resourceGroup `
	   -Location $originalVM.Location `
	   -VM $newVM `
	   -DisableBginfoExtension

With this, we're good at adding the availability set to the existing Azure VM. The above steps & PowerShell script was tested on Jun/July 2020. 


Reference:

1. https://docs.microsoft.com/en-us/azure/virtual-machines/windows/change-availability-set

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