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--- title: Update a Virtual Machine Scale Set with instance mix description: How to update a virtual machine scale set instance mix settings. author: brittanyrowe ms.author: brittanyrowe ms.topic: concept-article ms.service: azure-virtual-machine-scale-sets ms.date: 05/19/2026 ms.reviewer: wwilliams # Customer intent: As a cloud system administrator, I want to update the instance mix settings on a virtual machine scale set, so that I can optimize VM sizes and allocation strategies to better meet my application's performance and cost requirements. --- # Update instance mix settings on an existing scale set This article explains how to update the instance mix settings on a scale set, including changing VM sizes and allocation strategies. ## Update the instance mix settings on an existing scale set The instance mix settings can be updated on your scale set via CLI, PowerShell, and REST API. You can change either the virtual machine (VM) sizes or the allocation strategy, or both, in a single call. > [!NOTE] > When you change the allocation strategy, the new strategy takes effect only after the scale set scales in or out. Existing VMs aren't affected until a scaling action occurs. When changing from `Prioritized (preview)` to another allocation strategy, you must first nullify the priority ranks associated with the VM sizes. ### [Azure CLI](#tab/cli-1) Ensure you're using Azure CLI version `2.66.0` or later. #### Change the allocation strategy To update the allocation strategy, for example, to `CapacityOptimized`: ```azurecli-interactive az vmss update \ --resource-group {resourceGroupName} \ --name {scaleSetName} \ --set skuProfile.allocationStrategy=CapacityOptimized ``` #### Change the VM sizes To update the VM sizes in the `skuProfile`, for example, to Standard_D2as_v4, Standard_D2as_v5, and Standard_D2s_v5: > [!NOTE] > When you update VM sizes, you must specify the complete list of sizes you want in the scale set. This operation replaces the entire list, not just adds or removes individual sizes. ```azurecli-interactive az vmss update \ --resource-group {resourceGroupName} \ --name {scaleSetName} \ --skuprofile-vmsizes Standard_D2as_v4 Standard_D2as_v5 Standard_D2s_v5 ``` ### [Azure PowerShell](#tab/powershell-1) #### Change the allocation strategy To update the allocation strategy: ```azurepowershell-interactive # Set variable values $resourceGroupName = "resourceGroupName" $vmssName = "scaleSetName" $allocationStrategy = "CapacityOptimized" # Get the scale set $vmss = Get-AzVmss -ResourceGroupName $resourceGroupName -VMScaleSetName $vmssName # Update the allocation strategy $vmss.SkuProfile.AllocationStrategy = $allocationStrategy # Apply the update Update-AzVmss -ResourceGroupName $resourceGroupName -VMScaleSetName $vmssName -VirtualMachineScaleSet $vmss ``` #### Change the VM sizes To update the VM sizes: ```azurepowershell-interactive # Set variable values $resourceGroupName = "resourceGroupName" $vmssName = "scaleSetName" # Create a list of new VM sizes $vmSizeList = [System.Collections.Generic.List[Microsoft.Azure.Management.Compute.Models.SkuProfileVMSize]]::new() $vmSizeList.Add("Standard_D2as_v4") $vmSizeList.Add("Standard_D2as_v5") $vmSizeList.Add("Standard_D2s_v5") # Get the scale set $vmss = Get-AzVmss -ResourceGroupName $resourceGroupName -VMScaleSetName $vmssName # Update the VM sizes $vmss.SkuProfile.vmSizes = $vmSizeList # Apply the update Update-AzVmss -ResourceGroupName $resourceGroupName -VMScaleSetName $vmssName -VirtualMachineScaleSet $vmss ``` ### [REST API](#tab/arm-1) To update instance mix settings using the REST API, send a `PATCH` request to the scale set resource. Use API version `2023-09-01` or later: ```http PATCH https://management.azure.com/subscriptions/{YourSubscriptionId}/resourceGroups/{YourResourceGroupName}/providers/Microsoft.Compute/virtualMachineScaleSets/{yourScaleSetName}?api-version=2023-09-01 ``` #### Change the allocation strategy Specify both the VM sizes and the allocation strategy. For example, to set the allocation strategy to `capacityOptimized`: ```json { "properties": { "skuProfile": { "vmSizes": [ { "name": "Standard_D2as_v4" }, { "name": "Standard_D2as_v5" }, { "name": "Standard_D2s_v4" }, { "name": "Standard_D2s_v3" }, { "name": "Standard_D2s_v5" } ], "allocationStrategy": "capacityOptimized" } } } ``` #### Change the VM sizes To update only the VM sizes: ```json { "properties": { "skuProfile": { "vmSizes": [ { "name": "Standard_D2as_v4" }, { "name": "Standard_D2as_v5" }, { "name": "Standard_D2s_v4" }, { "name": "Standard_D2s_v3" }, { "name": "Standard_D2s_v5" } ] } } } ``` --- ## Enable instance mix on an existing scale set To enable instance mix on a scale set that doesn't already use it, specify the `skuProfile` properties. You must set: - `sku.name` to `"Mix"` - `sku.tier` to `null` - At least one value in `vmSizes` under `skuProfile` - An `allocationStrategy` (if not specified, Azure defaults to `lowestPrice`) The following examples show how to enable instance mix on an existing scale set. ### [Azure CLI](#tab/cli-2) This example updates an existing scale set in Flexible Orchestration Mode to use instance mix with VM sizes Standard_D2as_v4, Standard_D2s_v5, and Standard_D2as_v5, and the `capacityOptimized` allocation strategy: ```azurecli-interactive az vmss update \ --name {scaleSetName} \ --resource-group {resourceGroupName} \ --set sku.name=Mix sku.tier=null \ --skuprofile-vmsizes Standard_D2as_v4 Standard_D2s_v5 Standard_D2as_v5 \ --set skuProfile.allocationStrategy=capacityOptimized ``` ### [REST API](#tab/arm-2) To enable instance mix using the REST API, send a `PATCH` request to the scale set resource. Use API version `2023-09-01` or later: ```http PATCH https://management.azure.com/subscriptions/{YourSubscriptionId}/resourceGroups/{YourResourceGroupName}/providers/Microsoft.Compute/virtualMachineScaleSets/{yourScaleSetName}?api-version=2023-09-01 ``` In the request body, set `sku.name` to `"Mix"` and include the `skuProfile` with your desired `vmSizes` and `allocationStrategy`: ```json { "sku": { "name": "Mix" }, "properties": { "skuProfile": { "vmSizes": [ { "name": "Standard_D2as_v4" }, { "name": "Standard_D2as_v5" }, { "name": "Standard_D2s_v4" }, { "name": "Standard_D2s_v5" } ], "allocationStrategy": "lowestPrice" } } } ``` --- ## Common update scenarios ### Remove a specific VM size To remove a specific VM size from the instance mix configuration, specify the complete list of VM sizes you want to keep, excluding the size you want to remove. **Example**: Remove `Standard_D2as_v4` from a scale set that has `Standard_D2as_v4`, `Standard_D2s_v4`, `Standard_D2as_v5`, and `Standard_D2s_v5`: ```azurecli-interactive az vmss update \ --resource-group {resourceGroupName} \ --name {scaleSetName} \ --skuprofile-vmsizes Standard_D2s_v4 Standard_D2as_v5 Standard_D2s_v5 ``` ### Add a specific VM size To add a new VM size to the instance mix configuration, specify the complete list of VM sizes including both existing and new sizes. **Example**: Add `Standard_D4s_v5` to a scale set that currently has `Standard_D2s_v4`, `Standard_D2as_v5`, and `Standard_D2s_v5`: ```azurecli-interactive az vmss update \ --resource-group {resourceGroupName} \ --name {scaleSetName} \ --skuprofile-vmsizes Standard_D2s_v4 Standard_D2as_v5 Standard_D2s_v5 Standard_D4s_v5 ``` ## Next steps Learn how to [troubleshoot](instance-mix-faq-troubleshooting.md) your instance mix-enabled scale set.