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Deploy app service environments using availability zones#

Reliability · App Service Environment · Rule · 2024_09 · Important

Deploy app service environments using availability zones in supported regions to ensure high availability and resilience.

Description#

App Service Environments support zone redundancy, which distributes your application running within the environment across Availablity Zones. Each Availability Zone is a group of phyiscally separated data centers. Deploying your application with zone redundancy:

  • Scales your plan within the environment to a minimum of 3 instances in a highly available configuration. Additional instances can be added manually or on-demand by using autoscale.
  • Improves the resiliency against service disruptions or issues affecting a single zone.

Additionally:

  • Even Distribution: If the instance count is larger than 3 and divisible by 3, instances are evenly distributed across the three zones.
  • Partial Distribution: Instance counts beyond 3*N are spread across the remaining one or two zones to ensure balanced distribution.

Important Configuring zone redundancy with per-application scaling is possible but may increase costs and administrative overhead. When perSiteScaling is enabled, each application can have its own scaling rules and run on dedicated instances. To maintain zone redundancy, it is crucial that each application’s scaling rules ensure a minimum of 3 instances. Without explicitly configuring this minimum, the application may not meet the zone redundancy requirement.

Recommendation#

Consider using enabling zone redundancy using availability zones to improve the resiliency of your solution.

Examples#

Configure with Azure template#

To configure a zone-redundant app service environment:

  • Set the properties.zoneRedundant property to true.

For example:

Azure Template snippet
{
  "type": "Microsoft.Web/hostingEnvironments",
  "apiVersion": "2022-09-01",
  "name": "[parameters('name')]",
  "location": "[parameters('location')]",
  "kind": "ASEV3",
  "properties": {
    "zoneRedundant": true
  }
}

Configure with Bicep#

To configure a zone-redundant app service environment:

  • Set the properties.zoneRedundant property to true.

For example:

Azure Bicep snippet
resource ase 'Microsoft.Web/hostingEnvironments@2022-09-01' = {
  name: name
  location: location
  kind 'ASEV3'
  properties: {
    zoneRedundant: true
  }
}

Notes#

Zone-redundancy is only supported for the ASEV3 version.

Zone-redundancy is not supported for environments deployed on a dedicated host group.

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