Azure Subnet IP address space exhaustion failure experiment

dummy_nic.bicep

param prefix string = 'fillup'
param location string = resourceGroup().location
param vnetName string = 'my-vnet'
param subnetName string = 'my-snet'

param ipAddressesToCreate int = 600

resource subnet 'Microsoft.Network/virtualNetworks/subnets@2022-01-01' existing = {
  name: '${vnetName}/${subnetName}'
}

// Calculate the number of NICs to create. Each NIC can have up to 256 IP addresses.
var nicsToCreate = int(ipAddressesToCreate / 256) + 1

resource nic 'Microsoft.Network/networkInterfaces@2022-01-01' = [for n in range(0, nicsToCreate): {
  name: '${prefix}-${n}-test-nic'
  location: location
  properties: {
    ipConfigurations: [for i in range(0, n < nicsToCreate - 1 ? 256 : ipAddressesToCreate % 256): {
      name: 'ipconfig-${i}'
      properties: {
        subnet: {
          id: subnet.id
        }
        primary: i == 0
        privateIPAllocationMethod: 'Dynamic'
      }
    }]
  }
}]

output deployedNics array = [for i in range(0, nicsToCreate): {
  name: nic[i].name
  resourceId: nic[i].id
  numberOfIpAddresses: length(nic[i].properties.ipConfigurations)
}]

run_subnet_exhaustion.ps1

$targetSubscriptionId = "*******"

$targetResourceGroup = "my-rg"
$targetVnetName = "my-vnet"
$targetSubnetName = "my-snet"

$prefix = "chaosfill"

$experimentDurationSeconds = 30

# Fetch current VNet/subnets IP address allocation
$subnetSpace = az rest --method get `
               --url "/subscriptions/$targetSubscriptionId/resourceGroups/$targetResourceGroup/providers/Microsoft.Network/virtualNetworks/$targetVnetName/usages?api-version=2021-01-01" `
               | ConvertFrom-Json

$subnet = $subnetSpace | Select-Object -ExpandProperty value | Where-Object { $_.id -like "*/subnets/$targetSubnetName" }

$freeIpAddresses = $subnet.limit - $subnet.currentValue

Write-Host "Free IP addresses in subnet $($targetSubnetName): $freeIpAddresses"

if($freeIpAddresses -lt 1) {
    Write-Host "No free IP addresses in subnet. Subnet does not exist or is already full."
    exit
}

Write-Host "Starting ARM deployment to fill up the subnet"

$armDeployment = az deployment group create `
    --name "$prefix-deployment-$(Get-Date -Format "yyyyMMddHHmmss")" `
    --template-file .\dummy_nic.bicep `
    --resource-group $targetResourceGroup `
    --parameters `
    prefix=$prefix `
    vnetName=$targetVnetName `
    subnetName=$targetSubnetName `
    ipAddressesToCreate=$freeIpAddresses | ConvertFrom-Json

Write-Host "ARM deployment completed with status: $($armDeployment.properties.provisioningState)"

Write-Host "Sleeping for $experimentDurationSeconds seconds"
Start-Sleep -s $experimentDurationSeconds

$nics = $armDeployment.properties.outputs.deployedNics.value

Write-Host "Experiment finished. Deleting NICs to free up space again."

foreach($nic in $nics)
{
    Write-Host "Deleting NIC: $($nic.name)"
    az resource delete --ids $nic.resourceId
}