VMSS Automatic Zone Placement CLI Support #31951
Description
Preconditions
- No need to upgrade Python SDK or the Python SDK is ready.
Related command
az vmss create, az vmss update
Resource Provider
Microsoft.Compute/VMSS
Description of Feature or Work Requested
Automatic Zone Placement simplifies the process of deploying zonal resources by allowing the platform to determine the optimal zone(s) for allocations based on live capacity signals and customer constraints. SKU availability and zonal capacity can vary significantly across different Azure regions. Customers have limited insight into the capacity landscape for their SKUs, this can lead to sub-optimal zone selections and scaling challenges. With Automatic Zone Placement, customers no longer have to manually specify a "zones" list. VMSS will identify the "best" zones to deploy VMs based on capacity signals and customer-configured policies. Full overview of the current workflow is available here.
Minimum API Version Required
2024-07-01
Swagger PR link / SDK link
This feature will be part of the 2025-04-01 swagger release (not merged yet into main, expected to be merged by 8/21. SDKs will be generated after swagger is merged). Link to the PR for our swagger changes here.
We are aiming for Ignite Public Preview, so wanted to create this issue a bit earlier as we would need CLI support to be available by end of Oct / early Nov.
Once the swagger is rolled out, it should be available here (under 2025-04-01).
Relevant swagger parameters:
- "zonePlacementPolicy"
- "ZoneAllocationPolicy.MaxInstancePercentPerZonePolicy.enabled"
- "ZoneAllocationPolicy.MaxInstancePercentPerZonePolicy.value"
- "ZoneAllocationPolicy.MaxZoneCount"
Request Example
Impacted CLI Commands: az vmss create, az vmss update
We would like to support the following parameters on vmss create and update commands so that customers can use Automatic Zone Placement on their scale sets.
"--zone-placement-policy", { "Auto" }
- Whether Automatic Zone Placement with be applied for this VMSS. If customer has ZonePlacementPolicy specified, they cannot have the "zones" list on their VMSS.
"--max-zone-count", { int }
- The maximum number of zones across which instances will be spread. If maxZoneCount is not specified, the scale set will try to spread VMs across 3 AZs but may deploy to additional zones (4th, 5th AZ) when necessary to fulfill capacity requests.
"--enable-max-instance-percent-per-zone", { bool }
- If maxInstancePercentPerZone should be enabled. Customers will have to specify both enableMaxInstancePercentPerZone and valueMaxInstancePercentPerZone in order to apply maxInstancePercentPerZone on their VMSS.
"--value-max-instance-percent-per-zone", { int }
- The value for maximum % of VMs that can be allocated in a single zone.
- For example: if valueMaxInstancePercentPerZone = 50, this means that at any time, no more than 50% of the VMs in your scale set can be allocated to a single zone.
Target Date
Nov 21st, 2025
PM Contact
Engineer Contact
[email protected], [email protected], [email protected]
Additional context
Some properties that may conflict / cannot be enabled on the scale set if customer has Automatic Zone Placement
- "Overprovision", must be false if zonePlacementPolicy is being used on the scale set
- "ProximityPlacementGroupId", zonePlacementPolicy is currently not supported with proximity placement groups and capacity reservation groups.
- "zones", zonePlacementPolicy cannot be enabled if "zones" list exists on the scale set