When deploying an ARM-tempalate, the Azure Virtual Network got updated with the new DNS server. The Virtual machines deployed before this update, still got the old DNS client settings, before the VM gets rebooted. This becomes a bit of a challange, when trying to domain join the computer with Desired State Configuration (DSC), since it will not find the domain controller (if not the old DNS settings where already pointed to a current domain controller).

To force a reboot thru DSC can be achieved by the module xPendingReboot and DSC Script. xPendingReboot checks if there is a pending reboot of the machine and works in conjunction with the Local Configuration Manager (LCM). If LCM is set to RebootNodeIfNeeded=$true, it will reboot. However, a new machine got no pending reboot. To achieve this we will need to set DSCMachineStatus to 1 and write a small registry item. This will indicate there is a PendingReboot.

First we need to load the module (including the domainJoin as well)

Import-DscResource -ModuleName xPendingReboot, xDSCDomainjoin

Set the LCM RebootNodeIfNeeded to true

LocalConfigurationManager 
{
   RebootNodeIfNeeded = $true
}

Create a xPendingReboot resource

xPendingReboot Reboot
{
   Name = "Reboot"
}

Add our “fake” reboot.

Script Reboot
{
    TestScript = {
    return (Test-Path HKLM:\SOFTWARE\MyMainKey\RebootKey)
    }
    SetScript = {
			New-Item -Path HKLM:\SOFTWARE\MyMainKey\RebootKey -Force
			$global:DSCMachineStatus = 1 
        }
    GetScript = { return @{result = 'result'}}
}

and finally the domainjoin with a DependsOn so it will happend before domainjoin.

xDSCDomainjoin JoinDomain
{
  Domain = $DomainName
  Credential = $DomainCreds
  DependsOn = "[Script]Reboot"
}