Attach or detach a Virtual Machine to or from a Virtual Machine Scale Set

Grein
08/22/2024

Attaching a Virtual Machine to a Virtual Machine Scale Set

Important

You can only attach Virtual Machines to a Virtual Machine Scale Set in Flexible orchestration mode. For more information, see Orchestration modes for Virtual Machine Scale Sets.

There are times where you need to attach a virtual machine (VM) to a Virtual Machine Scale Set to benefit from the scale, availability, and flexibility that comes with scale sets. There are two ways to attach VMs to scale sets: manually create a new standalone VM in the scale set or attach an existing VM to the scale set.

You can attach a new standalone VM to a scale set when you need a different configuration on a specific VM than what's defined in the scaling profile, or when the scale set doesn't have a scaling profile. Manually attaching VMs gives you full control over instance naming and placement into a specific availability zone or fault domain. The VM doesn't have to match the configuration in the scale set's scaling profile, so you can specify parameters like operating system, networking configuration, on-demand or Spot, and VM size.

You can attach an existing VM to an existing Virtual Machine Scale Set by specifying which scale set you would like to attach to. The VM doesn't have to be the same as the VMs already running in the scale set, meaning it can have a different operating system, network configuration, priority, disk, and more.

Attach a new Virtual Machine to a Virtual Machine Scale Set

Attach a virtual machine to a Virtual Machine Scale Set at the time of VM creation by specifying the virtualMachineScaleSet property.

Note

Attaching a virtual machine to Virtual Machine Scale Set doesn't by itself update any VM networking parameters such as load balancers. If you would like this virtual machine to receive traffic from any load balancer, you must manually configure the VM network interface to receive traffic from the load balancer. Learn more about Load balancers.

Go to Virtual Machines.
Select Create.
Select Azure virtual machine.
In the Basics tab, open the Availability options dropdown and select Virtual Machine Scale Set.
In the Virtual Machine Scale Set dropdown, select the scale set to which you want to add this virtual machine.
Optionally, specify the Availability zone or Fault domain to place the VM.

az vm create 
  --name myVM \
  --resource-group myResourceGroup \
  --image Ubuntu2204 \
  --vmss myVMScaleSet \
  --platform-fault-domain 1

New-AzVm `
    -ResourceGroupName 'myResourceGroup' `
    -Name 'myVM' `
    -Location 'East US' `
    -VmssId 'myVmss' `
    -VirtualNetworkName 'myVnet' `
    -SubnetName 'mySubnet' `
    -SecurityGroupName 'myNetworkSecurityGroup' `
    -PublicIpAddressName 'myPublicIpAddress' `
    -OpenPorts 80,3389

Exceptions to attaching a new Virtual Machine to a Virtual Machine Scale Set

The VM must be in the same resource group as the scale set.
Regional virtual machines (no availability zones specified) can be attached to regional scale sets.
Zonal virtual machines can be attached to scale sets that specify one or more zone. The virtual machine must be in one of the zones spanned by the scale set. For example, you can't create a virtual machine in Zone 1, and place it in a scale set that spans Zones 2 and 3.
The scale set must be in Flexible orchestration mode, and the singlePlacementGroup property must be false.

Attach an existing Virtual Machine to a Virtual Machine Scale Set

Attach an existing virtual machine to a Virtual Machine Scale Set after the time of VM creation by specifying the virtualMachineScaleSet property. Attaching an existing VM to a scale set with a fault domain count of 1 doesn't require downtime.

Note

Go to Virtual Machines.
Select the name of the virtual machine you'd like to attach to your scale set.
Under Settings select Availability + scaling.
In the Scaling section, select the Get started button. If the button is grayed out, your VM currently doesn't meet the requirements to be attached to a scale set.
In the Attach to a VMSS blade on the right side of the page, select the scale set you'd like to attach the VM to in the Select a VMSS dropdown.
Select the Attach button at the bottom to attach the VM.

az vm update 
  --resource-group {resourceGroupName} \
  --name {vmName} \
  --set virtualMachineScaleSet.id='/subscriptions/{subscriptionID}/resourceGroups/{resourceGroupName}/providers/Microsoft.Compute/virtualMachineScaleSets/{scaleSetName}'

#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

Limitations for attaching an existing Virtual Machine to a scale set

The scale set must use Flexible orchestration mode.
The scale set must have a platformFaultDomainCount of 1.
The VM and scale set must be in the same resource group.
The VM and target scale set must both be zonal, or they must both be regional. You can't attach a zonal VM to a regional scale set.
The VM can't be in a self-defined availability set.
The VM can't be in a ProximityPlacementGroup.
The VM can't be in an Azure Dedicated Host.
The VM must have a managed disk.
The scale set must have singlePlacementGroup set to False.
Scale sets created without a scaling profile default to singlePlacementGroup set to null. To attach VMs to a scale set without a scaling profile, singlePlacementGroup needs to be set to False at the time of the scale set's creation.
The VM can't be a Remote Direct Memory Access (RDMA) capable HB-series or N-series VM.

Detaching a Virtual Machine from a Virtual Machine Scale Set

Should you need to detach a VM from a scale set, you can follow the below steps to remove the VM from the scale set.

Go to Virtual Machines.
Select the name of the virtual machine you'd like to attach to your scale set.
Under Settings select Availability + scaling.
Select the Detach from the VMSS button at the top of the page.
When prompted to confirm, select the Detach button.
Portal sends a notification when the VM is detached.

az vm update 
  --resource-group resourceGroupName \
  --name vmName \
  --set virtualMachineScaleSet.id=null

#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

Limitations for detaching a Virtual Machine from a scale set

The scale set must use Flexible orchestration mode.
The scale set must have a platformFaultDomainCount of 1.
Scale sets created without a scaling profile default to singlePlacementGroup set to null. To detach VMs from a scale set without a scaling profile, singlePlacementGroup needs to be set to False.
The VM can't be an RDMA capable HB-series or N-series VM.

Moving Virtual Machines between scale sets

To move a VM from one scale set to another, use the following steps:

Detach the VM from scale set A.
Once the detach completes, attach the VM to scale set B.

Limitations

The limitations for VMs to be attached or detached to or from a scale set remain the same.

Troubleshooting

Attach an existing Virtual Machine to an existing scale set troubleshooting

Error Message	Description	Troubleshooting Options
The Virtual Machine Scale Set '{vmssUri}' referenced by the Virtual Machine does not exist.	The scale set resource doesn't exist, or isn't in Flexible Orchestration Mode.	Check to see if the scale set exists. If it does, check if it's using Uniform Orchestration Mode.
This operation is not allowed because referenced Virtual Machine Scale Set '{vmssName}' does not have orchestration mode set to 'Flexible'.	The scale set isn't in Flexible Orchestration Mode.	Try attaching to another scale set with Flexible Orchestration Mode enabled.
Referenced Virtual Machine '{vmName}' belongs to an Availability Set and attaching to a Virtual Machine Scale Set is not supported. For more information, see https://aka.ms/vmo/attachdetach.	`VmssDoesNotSupportAttachingExistingAvsetVM`: The VM that you attempted to attach is part of an Availability Set and can't be attached to a scale set.	VMs in an Availability Set can't be attached to a scale set.
Referenced Virtual Machine Scale Set '{vmssName}' does not support attaching an existing Virtual Machine to it because the Virtual Machine Scale Set has more than 1 fault domains. For more information, see https://aka.ms/vmo/attachdetach.	`VmssDoesNotSupportAttachingExistingVMMultiFD`: The operation to attach the VM failed because the VM was trying to attach to a scale set with a platform fault domain count of more than one.	VMs can only be attached to scale sets with a `platform fault domain count` of 1. Try attaching to a scale set with a platform fault domain count of one.
Using a Virtual Machine '{vmName}' with unmanaged disks and attaching it to a Virtual Machine Scale Set is not supported. For more information, see https://aka.ms/vmo/attachdetach.	`VmssDoesNotSupportAttachingExistingVMUnmanagedDisk`: VMs with unmanaged disks can't be attached to a scale set.	To attach a VM with a disk to the scale set, ensure that the VM is using a managed disk. Visit the documentation to learn how to migrate from an unmanaged disk to a managed disk.
Referenced Virtual Machine '{vmName}' belongs to a proximity placement group (PPG) and attaching to a Virtual Machine Scale Set is not supported. For more information, see https://aka.ms/vmo/attachdetach.	`VmssDoesNotSupportAttachingPPGVM`: The operation to attach the VM failed because the VM is part of a Proximity Placement Group.	VMs from a Proximity Placement Group can't be attached to a scale set. Remove the VM from the Proximity Placement Group and then try to attach to the scale set. See the documentation to learn about how to move a VM out of a Proximity Placement Group.
PropertyChangeNotAllowed Changing property virtualMachineScaleSet.id isn't allowed.	The Virtual Machine Scale Set ID can't be changed to a different Virtual Machine Scale Set ID without detaching the VM from the scale set first.	Detach the VM from the Virtual Machine Scale Set, and then attach to the new scale set.
Virtual Machine Scale Set '{0}' does not support attaching an existing Virtual Machine to it because the Virtual Machine Scale Set has single placement group set to true or does not have single placement group explicitly set to false. Please see https://aka.ms/vmo/attachdetach for more information.	`VmssDoesNotSupportAttachingWithSpg`: The operation for attaching the VM failed because the scale set is part of a Single Placement Group.	VMs can only be attached to scale sets with `singlePlacementGroup` set to `false`.
Virtual Machine Scale Set does not support attaching Virtual Machine {0} because it uses VM Size {1} which can be only be used with a single placement group enabled Virtual Machine Scale Set. Please see https://aka.ms/vmo/attachdetach for more information.	The VM being attached is of a size that requires the scale set to use a Single Placement Group.	VMs requiring Single Placement Group can't be attached to a scale set.
Virtual Machine Scale Set does not support attaching RDMA capable VM Sizes such as {0}. Please see https://aka.ms/vmo/attachdetach for more information.	RDMA capable VMs can't be detached from the scale set. The detach failed because the VM is RDMA capable.	Only VMs that aren't RDMA enabled can be detached from the scale set.

Detach a Virtual Machine from a scale set troubleshooting

Error Message	Description	Troubleshooting options
The Virtual Machine Scale Set '{vmssUri}' referenced by the Virtual Machine does not exist.	The scale set resource doesn't exist, or isn't in Flexible Orchestration Mode.	Check to see if the scale set exists. If it does, check if it's using Uniform Orchestration Mode.
This operation is not allowed because referenced Virtual Machine Scale Set '{vmssName}' does not have orchestration mode set to 'Flexible'.	The scale set isn't in Flexible Orchestration Mode.	Only scale sets with Flexible Orchestration Mode can have VMs detached from them.
Virtual Machine Scale Set '{vmssName}' does not support detaching an existing Virtual Machine from it because the Virtual Machine Scale Set has more than 1 fault domains. For more information, see https://aka.ms/vmo/attachdetach.	The detach of the VM failed because the scale set it's in has more than one platform fault domain.	VMs can only be detached from scale sets with a `platform fault domain count` of one.
OperationNotAllowed, Message: This operation is not allowed because referenced Virtual Machine Scale Set '{armId}' does not have orchestration mode set to 'Flexible'	The scale set you attempted to attach to or detach from is a scale set with Uniform Orchestration Mode.	Only scale sets with Flexible Orchestration Mode can have VMs detached from them.
PropertyChangeNotAllowed Changing property virtualMachineScaleSet.id is not allowed.	The Virtual Machine Scale Set ID can't be changed to a different Virtual Machine Scale Set ID without detaching the VM from the scale set first.	Detach the VM from the Virtual Machine Scale Set, and then attach to the new scale set. Ensure the `virtualMachineScaleSet.id` is set to the value of `null`. Incorrect values include: `""` and `"null"`.
Virtual Machine Scale Set '{0}' does not support detaching Virtual Machine from it because the Virtual Machine Scale Set has single placement group set to true. Please see https://aka.ms/vmo/attachdetach for more information.	`VmssDoesNotSupportAttachingWithSpg`: The detach of the VM failed because the scale set is part of a Single Placement Group.	VMs can only be detached from scale sets with `singlePlacementGroup` set to `false`.
Virtual Machine Scale Set does not support detaching RDMA capable VM Sizes such as {0}. Please see https://aka.ms/vmo/attachdetach for more information.	RDMA capable VMs can't be detached from the scale set. The detach failed because the VM is RDMA capable.	Only VMs that aren't RDMA enabled can be detached from the scale set.

What's next

Learn how to manage updates and maintenance using Maintenance notification, Maintenance configurations, and Scheduled Events.

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