Understanding and Mapping Logical to Physical Availability Zones in Azure

When deploying Azure-based solutions, understanding the difference between logical and physical Availability Zones (AZs) is critical.

Overview

When deploying Azure-based solutions, understanding the difference between logical and physical Availability Zones (AZs) is critical. Logical AZs are identifiers that Microsoft Azure exposes within a subscription, such as Zone 1, Zone 2, or Zone 3. However, these logical zones are not consistent across subscriptions. This means that Zone 1 in one subscription may map to a different physical datacenter compared to Zone 1 in another subscription. Further information about this subject can be found on Azure's website.

This discrepancy can create challenges when deploying services such as Everpure Cloud Dedicated or Everpure Cloud solutions across multiple subscriptions. If logical AZs do not align with the same underlying physical datacenter, performance, high availability and disaster recovery strategies may be impacted. This is particularly important when integrating Everpure Cloud products with Azure VMware Solution as placing the two instances in two separate physical datacenters will lead to sub-optimal performance due to additional unnecessary networking hops.

How to Determine Logical vs Physical Availability Zone Mappings

Azure provides a method to query physical zone mappings per subscription using the Azure CLI. This allows customers to verify which logical zone corresponds to which physical datacenter.

Azure CLI Command Example:

az rest --method get --uri '/subscriptions/{subscriptionId}/locations?api-version=2022-12-01' --query 'value[?availabilityZoneMappings != `null`].{displayName: displayName, name: name, availabilityZoneMappings: availabilityZoneMappings}'

Sample Output:

  {
    "availabilityZoneMappings": [
      {
        "logicalZone": "1",
        "physicalZone": "centralus-az2"
      },
      {
        "logicalZone": "2",
        "physicalZone": "centralus-az3"
      },
      {
        "logicalZone": "3",
        "physicalZone": "centralus-az1"
      }
    ],

Repeat the above command for each unique Azure subscription to determine the physical AZ for each.

Ensure that all integrated components across multiple subscriptions are deployed into the same Physical Availability Zone. This potentially will mean deploying into different logical AZs for each subscription depending on the results from the above commands.

Azure's logical vs physical Availability Zone distinction is crucial for customers operating across multiple subscriptions. Without validating mappings, deployments may be unintentionally spread across separate datacenters, impacting performance and resilience. Using the Azure CLI, customers can map logical to physical AZs and ensure deployments are correctly aligned.