VM Scale Set should enable automatic OS upgrades

Medium Azure General virtualmachinescalesets-vmss

Applies to

Microsoft.Compute/virtualMachineScaleSets

What CGPulse checks

A resource passes this rule when enableAutomaticOSUpgrade must equal true. Anything else is reported as a finding with the evaluated property value attached as evidence.

How to fix it

Enable automatic OS upgrades to receive critical security patches. In Azure Portal: VMSS > Upgrade policy > enable Automatic OS upgrades. See: https://learn.microsoft.com/en-us/azure/virtual-machine-scale-sets/virtual-machine-scale-sets-automatic-upgrade

CLI

az vmss update --ids "{id}" --set upgradePolicy.automaticOSUpgradePolicy.enableAutomaticOSUpgrade=true

Terraform

resource "azurerm_linux_virtual_machine_scale_set" "{name}" {
  name                = "{name}"
  resource_group_name = "{rg}"
  location            = var.location
  sku                 = "Standard_DS1_v2"
  instances           = 2
  admin_username      = "adminuser"
  upgrade_mode        = "Automatic"
  automatic_os_upgrade_policy {
    enable_automatic_os_upgrade = true
    disable_automatic_rollback  = false
  }
  rolling_upgrade_policy {
    max_batch_instance_percent              = 20
    max_unhealthy_instance_percent          = 20
    max_unhealthy_upgraded_instance_percent = 5
    pause_time_between_batches              = "PT0S"
  }
  source_image_reference {
    publisher = "Canonical"
    offer     = "0001-com-ubuntu-server-jammy"
    sku       = "22_04-lts"
    version   = "latest"
  }
  os_disk {
    caching              = "ReadWrite"
    storage_account_type = "Standard_LRS"
  }
  network_interface {
    name    = "{name}-nic"
    primary = true
    ip_configuration {
      name      = "internal"
      primary   = true
      subnet_id = azurerm_subnet.{name}.id
    }
  }
}

Compliance frameworks

Cloud Security: Azure Foundations

Vendor documentation

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