Scale Set is attached to a load balancer backend pool

# Attach VMSS to an existing Load Balancer backend pool
resource "azurerm_linux_virtual_machine_scale_set" "<example_resource_name>" {
  name                = "<example_resource_name>"
  resource_group_name = "<example_resource_name>"
  location            = "<example_location>"
  sku                 = "Standard_DS1_v2"
  instances           = 1

  admin_username                  = "azureuser"
  disable_password_authentication = true
  admin_ssh_key {
    username   = "azureuser"
    public_key = "<SSH_PUBLIC_KEY>"
  }

  source_image_reference {
    publisher = "Canonical"
    offer     = "0001-com-ubuntu-server-jammy"
    sku       = "22_04-lts"
    version   = "latest"
  }

  network_interface {
    name    = "nic"
    primary = true
    ip_configuration {
      name                                   = "ipcfg"
      primary                                = true
      subnet_id                              = "<example_resource_id>"
      load_balancer_backend_address_pool_ids = ["<example_resource_id>"] # CRITICAL: associates VMSS with LB backend pool
    }
  }
}

// Associate VMSS with a Load Balancer backend pool
resource vmss 'Microsoft.Compute/virtualMachineScaleSets@2023-09-01' = {
  name: '<example_resource_name>'
  location: resourceGroup().location
  properties: {
    virtualMachineProfile: {
      networkProfile: {
        networkInterfaceConfigurations: [
          {
            name: 'nic'
            properties: {
              ipConfigurations: [
                {
                  name: 'ipcfg'
                  properties: {
                    loadBalancerBackendAddressPools: [
                      { id: '<example_resource_id>' } // CRITICAL: attach VMSS NIC IP config to LB backend pool
                    ]
                  }
                }
              ]
            }
          }
        ]
      }
    }
  }
}