Azure Stack Hub VM features

Azure Stack Hub virtual machines (VMs) provide on-demand, scalable computing resources. Before you deploy VMs, you should learn the differences between the VM features available in Azure Stack Hub and Microsoft Azure. This article describes these differences and identifies key considerations for planning VM deployments. To learn about high-level differences between Azure Stack Hub and Azure, see the Key considerations article.

VM differences

VM sizes

Azure Stack Hub imposes resource limits to avoid over consumption of resources (server local and service-level.) These limits improve the tenant experience by reducing the affect resource consumption by other tenants.

• For networking egress from the VM, there are bandwidth caps in place. Caps in Azure Stack Hub are the same as the caps in Azure.
• For storage resources, Azure Stack Hub implements storage IOPS (Input/Output Operations Per Second) limits to avoid basic overconsumption of resources by tenants for storage use.
• For VM disks, disk IOPS on Azure Stack Hub is a function of VM size instead of the disk type. This means that for a Standard_Fs series VM, regardless of whether you choose SSD or HDD for the disk type, the IOPS limit for an second data disk is 2300 IOPS.
• Temp disks attached to the VM are not persistent and can be lost on control plane operations such as resize or stop-deallocate.

The following table lists the VMs that are supported on Azure Stack Hub along with their configuration:

VM sizes and their associated resource quantities are consistent between Azure Stack Hub and Azure. This consistency includes the amount of memory, the number of cores, and the number/size of data disks that can be created. However, performance of VMs with the same size depends on the underlying characteristics of a particular Azure Stack Hub environment.

VM extensions

Azure Stack Hub includes a small set of extensions. Updates and additional extensions are available through Marketplace syndication. Bringing custom extensions into Azure Stack Hub is not a supported scenario; an extension must first be onboarded to Azure to be made available in Azure Stack Hub.

Use the following PowerShell script to get the list of VM extensions that are available in your Azure Stack Hub environment.

Get-AzVmImagePublisher -Location local | `
  Get-AzVMExtensionImageType | `
  Get-AzVMExtensionImage | `
  Select Type, Version | `
  Format-Table -Property * -AutoSize

Get-AzureRMVmImagePublisher -Location local | `
  Get-AzVMExtensionImageType | `
  Get-AzVMExtensionImage | `
  Select Type, Version | `
  Format-Table -Property * -AutoSize

If provisioning an extension on a VM deployment takes too long, let the provisioning timeout instead of trying to stop the process to deallocate or delete the VM.

API versions

VM features in Azure Stack Hub support the following API versions:

"2017-12-01", "2017-03-30", "2016-03-30", "2015-06-15"

You can use the following PowerShell script to get the API versions for the VM features that are available in your Azure Stack Hub environment:

Get-AzResourceProvider | `
  Select ProviderNamespace -Expand ResourceTypes | `
  Select * -Expand ApiVersions | `
  Select ProviderNamespace, ResourceTypeName, @{Name="ApiVersion"; Expression={$_}} | `
  where-Object {$_.ProviderNamespace -like "Microsoft.compute"}

Get-AzureRMResourceProvider | `
  Select ProviderNamespace -Expand ResourceTypes | `
  Select * -Expand ApiVersions | `
  Select ProviderNamespace, ResourceTypeName, @{Name="ApiVersion"; Expression={$_}} | `
  where-Object {$_.ProviderNamespace -like "Microsoft.compute"}

The list of supported resource types and API versions may vary if the cloud operator updates your Azure Stack Hub environment to a newer version.

Windows activation

Windows products must be used in accordance with Product Use Rights and Microsoft license terms. Azure Stack Hub uses Automatic VM Activation (AVMA) to activate Windows Server VMs.

• Azure Stack Hub host activates Windows with AVMA keys for Windows Server 2016. All VMs that run Windows Server 2012 R2 or later are automatically activated.
• VMs that run Windows Server 2012 or earlier aren't automatically activated and must be activated by using MAK activation. To use MAK activation, you must provide your own product key.

Microsoft Azure uses KMS activation to activate Windows VMs. If you move a VM from Azure Stack Hub to Azure and encounter activation problems, see Troubleshoot Azure Windows VM activation problems. Additional info can be found at the Troubleshooting Windows activation failures on Azure VMs Azure Support Team Blog post.

High Availability

Your VM may be subject to a reboot due to planned maintenance as scheduled by the Azure Stack Hub operator. For high availability of a multi-VM production system in Azure, VMs are placed in an availability set that spreads them across multiple fault domains and update domains. In the smaller scale of Azure Stack Hub, a fault domain in an availability set is defined as a single node in the scale unit.

While the infrastructure of Azure Stack Hub is already resilient to failures, the underlying technology (failover clustering) still incurs some downtime for VMs on an impacted physical server if there's a hardware failure. Azure Stack Hub supports having an availability set with a maximum of three fault domains to be consistent with Azure.

Fault domains

VMs placed in an availability set will be physically isolated from each other by spreading them as evenly as possible over multiple fault domains (Azure Stack Hub nodes). If there's a hardware failure, VMs from the failed fault domain will be restarted in other fault domains. They'll be kept in separate fault domains from the other VMs but in the same availability set if possible. When the hardware comes back online, VMs will be rebalanced to maintain high availability.

Update domains

Update domains are another way that Azure provides high availability in availability sets. An update domain is a logical group of underlying hardware that can undergo maintenance at the same time. VMs located in the same update domain will be restarted together during planned maintenance. As tenants create VMs within an availability set, the Azure platform automatically distributes VMs across these update domains.

In Azure Stack Hub, VMs are live migrated across the other online hosts in the cluster before their underlying host is updated. Since there's no tenant downtime during a host update, the update domain feature on Azure Stack Hub only exists for template compatibility with Azure. VMs in an availability set will show 0 as their update domain number on the portal.

Arc on Azure Stack Hub VMs

Arc enabled servers do not support installing the connected machine agent on virtual machines running in Azure, or virtual machines running on Azure Stack Hub or Azure Stack Edge, as they are already modeled as Azure VMs.

Microsoft Office server products on Azure Stack Hub VMs

Not all Microsoft Office server products are supported on Azure Stack Hub VMs, which is clarified as follows:

Next steps

Create a Windows VM with PowerShell in Azure Stack Hub