Skip to content

Deploy virtual machine scale set instances using availability zones#

Reliability · Virtual Machine Scale Sets · Rule · 2024_06 · Important

Deploy virtual machine scale set instances using availability zones in supported regions to ensure high availability and resilience.

Description#

Virtual machine scale sets (VMSS) supports the use of availability zones to provide redundancy across physically separated zones. When new instances are added to the VMSS as it scales, these instances are deployed across any zones that are configured.

For example:

  • If the VMSS is configured to use only Zone 1, all new instances will be created in Zone 1.
  • If the VMSS is configured to use three zones (Zone 1, Zone 2, and Zone 3), new instances will be distributed across these zones.

Also note:

  • Using availability zones is suitable for stateless workloads.
  • During scale-in operations, the number of instances in each zone may not be evenly distributed for all zones.

See documentation references below for additional limitations and important information.

Recommendation#

Consider configuring VM scale sets to spread instances across at least two (2) availability zones to improve resiliency to issues impacting a zone.

Examples#

Configure with Azure template#

To set availability zones for a virtual machine scale set:

  • Set zones to a minimum of two zones from ["1", "2", "3"].

For example:

Azure Template snippet
{
  "type": "Microsoft.Compute/virtualMachineScaleSets",
  "apiVersion": "2023-09-01",
  "name": "[parameters('name')]",
  "location": "[parameters('location')]",
  "sku": {
    "name": "b2ms",
    "tier": "Standard",
    "capacity": 3
  },
  "zones": [
    "1",
    "2",
    "3"
  ]
}

Configure with Bicep#

To set availability zones for a virtual machine scale set:

  • Set zones to a minimum of two zones from ["1", "2", "3"].

For example:

Azure Bicep snippet
resource vmss 'Microsoft.Compute/virtualMachineScaleSets@2023-09-01' = {
  name: name
  location: location
  sku: {
    name: 'b2ms'
    tier: 'Standard'
    capacity: 3
  }
  zones: [
    '1'
    '2'
    '3'
  ]
}

Comments