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 are not 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. This will be covered in more detail in the supporting code snippets.
Ensure you are using Azure CLI version 2.66.0 or later.
Change the allocation strategy
To update the allocation strategy, for example, to CapacityOptimized:
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:
az vmss update \
--resource-group {resourceGroupName} \
--name {scaleSetName} \
--skuprofile-vmsizes Standard_D2as_v4 Standard_D2as_v5 Standard_D2s_v5
Change the allocation strategy
To update the allocation strategy:
# 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:
# 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
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:
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:
{
"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:
{
"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 does not 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.
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:
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 \
--sku-allocat-strat capacityOptimized
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:
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:
{
"sku": {
"name": "Mix"
},
"properties": {
"skuProfile": {
"vmSizes": [
{ "name": "Standard_D2as_v4" },
{ "name": "Standard_D2as_v5" },
{ "name": "Standard_D2s_v4" },
{ "name": "Standard_D2s_v5" }
],
"allocationStrategy": "lowestPrice"
}
}
}
Next steps
Learn how to troubleshoot your instance mix-enabled scale set.