General Availability of Attach and Detach of Virtual Machines on Virtual Machine Scale Sets

Today, we are excited to announce that the ability to attach or detach virtual machines (VMs) to a Virtual Machine Scale Set (VMSS) without downtime is now generally available. This feature is available for scale sets with Flexible Orchestration Mode and a fault domain count of 1.

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1. Get things done in Azure: Easily move from a single VM to VMSS Flex and take advantage of all the benefits that scale sets provide, including auto-scaling, automatic OS upgrades, Spot priority mixing, instance recovery, and upgrade policies.
2. Easily scalable: Attaching existing VMs to an existing VMSS Flex allows you to scale compute without having to rebuild from scratch.
3. No downtime: You can create a seamless experience when using scale sets by attaching running VMs to scale sets without any downtime.
4. Solving Isolated Problems: If you need to troubleshoot a VM further, you can now isolate it from the scale set by detaching the VM.
5. Move VMs easily: This feature allows you to easily move VMs between scale sets, allowing you to group VMs as desired.

Once your VM and VMSS meet all the qualifications, you can quickly attach the VM to the scale set by updating the VM to use the VMSS ID. You can attach the VM via the REST API, Azure Portal, Azure CLI, or Azure PowerShell. For example, using PowerShell:

#Get VM information
$vm = Get-AzVM -ResourceGroupName $resourceGroupName -Name $vmName `

#Get scale set information
$vmss = Get-AzVmss -ResourceGroupName $resourceGroupName -Name $vmssName `

#Update the VM with the scale set ID
Update-AzVM -ResourceGroupName $resourceGroupName -VM $vm  -VirtualMachineScaleSetId $vmss.Id

Conversely, to detach a VM from a scale set, you can update the VM so that it no longer uses the VMSS ID.

#Get VM information
$vm = Get-AzVM -ResourceGroupName $resourceGroupName -Name $vmName

#Update the VM with the new scale set refence of $null
Update-AzVM -ResourceGroupName $resourceGroupName -VM $vm -VirtualMachineScaleSetId $null

The ability to attach and detach VMs to a VMSS Flex with fault domain count of 1 is generally available in Azure.

Learn more

For more information on how to attach or detach VMs to VMSS Flex, visit: documentation.