Table of Contents

Get-AzAvailabilityZoneMapping.ps1

Maps logical availability zones to physical datacenters across Azure subscriptions to ensure proper fault domain alignment.

Overview

Azure randomizes the mapping between logical zones (1, 2, 3) and physical datacenters for each subscription. This means logical zone 1 in subscription A might map to a completely different physical datacenter than zone 1 in subscription B. This script reveals these mappings, which is critical for multi-subscription architectures requiring true zone alignment.

Key capabilities

  • Physical zone discovery: Reveals actual physical datacenter identifiers
  • Cross-subscription mapping: Shows how zones align across multiple subscriptions
  • Compliance validation: Ensures deployments meet data residency requirements
  • Architecture planning: Essential data for multi-subscription deployment patterns

When to use this script

  • Planning multi-subscription deployments with zone redundancy
  • Verifying zone alignment before deployment stamp creation
  • Troubleshooting zone-related deployment failures
  • Compliance audits requiring physical datacenter documentation
  • Capacity reservation planning across subscriptions

Prerequisites

# Install Azure PowerShell module
Install-Module -Name Az -Repository PSGallery -Force

# Authenticate to Azure
Connect-AzAccount

# Verify subscription access
Get-AzSubscription | Select-Object Name, Id, State

# Ensure you have Reader access to target subscriptions
Get-AzRoleAssignment | Where-Object {$_.RoleDefinitionName -like "*Reader*"}

Parameters

Parameter Type Description Default
SubscriptionIds String[] Array of subscription IDs to analyze All accessible subscriptions
OutputFile String CSV output filename ZonePeers.csv

Usage examples

Basic usage - all subscriptions

.\Get-AzAvailabilityZoneMapping.ps1

Specific subscriptions for deployment planning

.\Get-AzAvailabilityZoneMapping.ps1 `
    -SubscriptionIds @('prod-sub-guid', 'dr-sub-guid') `
    -OutputFile "ProdDRZoneAlignment.csv"

Multi-subscription stamp validation

# Get all production subscription IDs
$prodSubs = Get-AzSubscription | Where-Object Name -like "Prod-*" | Select-Object -ExpandProperty Id

# Analyze zone mappings
.\Get-AzAvailabilityZoneMapping.ps1 `
    -SubscriptionIds $prodSubs `
    -OutputFile "ProductionZoneMappings_$(Get-Date -Format 'yyyyMMdd').csv"

Sample output

Running the script across multiple subscriptions produces output like this:

TenantId,SubscriptionId,SubscriptionName,Location,LogicalZone,PhysicalZone,PhysicalZoneName
12345678-1234-1234-1234-123456789012,abcd1234-5678-90ab-cdef-123456789012,Production-Primary,eastus,1,2,eastus-az2
12345678-1234-1234-1234-123456789012,abcd1234-5678-90ab-cdef-123456789012,Production-Primary,eastus,2,3,eastus-az3
12345678-1234-1234-1234-123456789012,abcd1234-5678-90ab-cdef-123456789012,Production-Primary,eastus,3,1,eastus-az1
12345678-1234-1234-1234-123456789012,efgh5678-90ab-cdef-1234-567890abcdef,Production-Secondary,eastus,1,3,eastus-az3
12345678-1234-1234-1234-123456789012,efgh5678-90ab-cdef-1234-567890abcdef,Production-Secondary,eastus,2,1,eastus-az1
12345678-1234-1234-1234-123456789012,efgh5678-90ab-cdef-1234-567890abcdef,Production-Secondary,eastus,3,2,eastus-az2
12345678-1234-1234-1234-123456789012,ijkl9012-3456-7890-abcd-ef1234567890,Development,eastus,1,1,eastus-az1
12345678-1234-1234-1234-123456789012,ijkl9012-3456-7890-abcd-ef1234567890,Development,eastus,2,2,eastus-az2
12345678-1234-1234-1234-123456789012,ijkl9012-3456-7890-abcd-ef1234567890,Development,eastus,3,3,eastus-az3

Understanding the output

  • TenantId: Azure AD tenant identifier
  • SubscriptionId: Unique subscription identifier
  • SubscriptionName: Friendly subscription name
  • Location: Azure region
  • LogicalZone: The zone number applications see (1, 2, 3)
  • PhysicalZone: Actual physical datacenter identifier
  • PhysicalZoneName: Full physical datacenter name

Critical findings from sample

In this example:

  • Production-Primary: Logical zone 1 → Physical zone 2
  • Production-Secondary: Logical zone 1 → Physical zone 3
  • Development: Logical zone 1 → Physical zone 1

This means deploying to "zone 1" across these subscriptions would actually spread resources across three different physical datacenters, defeating zone alignment goals.

Real-world implications

Incorrect assumption

Deploy to Zone 1 in all subscriptions = Same physical datacenter ❌

Reality revealed by script

Subscription A Zone 1 = Physical Datacenter 2
Subscription B Zone 1 = Physical Datacenter 3
Subscription C Zone 1 = Physical Datacenter 1
Result: No actual zone alignment! ⚠️

Correct approach

Use script output to map deployments:
- Subscription A: Deploy to Zone 3 (Physical DC 1)
- Subscription B: Deploy to Zone 2 (Physical DC 1)
- Subscription C: Deploy to Zone 1 (Physical DC 1)
Result: True zone alignment ✅

Troubleshooting

No zone data returned

# Verify the region supports availability zones
Get-AzLocation | Where-Object Location -eq 'eastus' | Select-Object -ExpandProperty Zones

# Check if subscription has zone access
Get-AzComputeResourceSku -Location 'eastus' |
    Where-Object {$_.LocationInfo.Zones.Count -gt 0} |
    Select-Object -First 5

Access denied errors

# Verify role assignments
Get-AzRoleAssignment -SignInName (Get-AzContext).Account.Id

# Switch to correct subscription context
Set-AzContext -SubscriptionId 'target-subscription-id'

Performance optimization

For large numbers of subscriptions:

# Process in batches
$allSubs = Get-AzSubscription | Select-Object -ExpandProperty Id
$batchSize = 10

for ($i = 0; $i -lt $allSubs.Count; $i += $batchSize) {
    $batch = $allSubs[$i..([Math]::Min($i + $batchSize - 1, $allSubs.Count - 1))]
    .\Get-AzAvailabilityZoneMapping.ps1 `
        -SubscriptionIds $batch `
        -OutputFile "ZoneMapping_Batch_$($i / $batchSize + 1).csv"
}

Integration patterns

Excel analysis

  1. Import CSV into Excel
  2. Create pivot table by Physical Zone
  3. Filter by Location
  4. Identify subscription groups with matching physical zones

Automated deployment alignment

# Load zone mappings
$zoneMappings = Import-Csv "ZonePeers.csv"

# Find subscriptions where logical zone 1 maps to physical zone 1
$alignedSubs = $zoneMappings |
    Where-Object {$_.LogicalZone -eq 1 -and $_.PhysicalZone -eq 1} |
    Select-Object -Unique SubscriptionId, SubscriptionName

# Deploy to these subscriptions in zone 1 for alignment

Script source

View full script source →

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