Charlie Russel's Blog

Creating VMs with New-myVM.ps1 - Part 1

As we saw in Part 1 of this series, I build my labs almost entirely with Windows PowerShell scripts. In that first post, I showed how to set the MAC address range on a Hyper-V host. I use this MAC address range to explicitly set my lab VMs to a specific MAC address for their NICs. This allows me to pre-configure all the IP addresses in DHCP by using reservations. (I showed you how to install and preconfigure the DHCP Server role in my post on Configuring Windows Server 2016 core as a DHCP Server with PowerShell. And I'll show you how to create all those reservations automatically in a later post in this series.)

For this post, and the couple, I want to share my "New-myVM.ps1" script. I use this script to create client and server VMs, from either DVD or sysprep'd VHDX files.

First, the parameters that New-myVM accepts:

[CmdletBinding()]
Param ([Parameter(Mandatory = $True,Position = 0)][alias("Name")][string]$VmName,
       [Parameter(Mandatory = $True,Position = 1)][alias("Final")][string]$MacFinal,
       [Parameter(Mandatory = $False)][alias("Base")][string]$MacBase = "00-15-5D-C8-0A-",
       [Parameter(Mandatory = $False)][string]$199MacBase = "00-15-5D-C8-CE-",
       [Parameter(Mandatory=$False)][alias("ISO")][Switch]$DVD,
       [Parameter(Mandatory=$False)][Boolean]$Client=($myInvocation.myCommand.Name -match "Client"),
       [Parameter(Mandatory=$False)][alias("Target")][string]$Path = "V:\",
       [Parameter(Mandatory=$False)][alias("VHDSource","DVDBase")][string]$Source = "V:\Source",
       [Parameter(Mandatory=$False)][alias("LocalSwitch","Network")][string]$vmSwitch = "10 Network",
       [Parameter(Mandatory=$False)][switch]$2012R2
       )

I have only two required parameters, the VMName and final two digits of the MAC addresses that the VM will use. Everything else defaults to some reasonable value for my labs. You'll notice that by default, I don't install from DVD, and I'm not installing Server 2012R2, but Server 2016. And, finally, a bit you might not have seen before, my default to determine if this is a client build or a server build.

[Parameter(Mandatory=$False)][Boolean]$Client=($myInvocation.myCommand.Name -match "Client")

The $Client parameter is a Boolean. I can specify it on the command line with -Client $True/$False, or I can allow it to accept the default value. The interesting thing is that the default value is dynamic. I use an NTFS hard link for New-myVM.ps1 to give it a second name, New-myClientVM.ps1.

Sidebar: NTFS Hard Links 

NTFS filesystem hard links take a single file and give it multiple names. The file is stored only once on the filesystem, but it has multiple names that can access the file. Each name for the file is completely equal. Even if you delete the original filename, all the linked versions are still present and completely unaffected by the deletion. You create a hard link in Server 2016 or Windows 10 with New-Item or in earlier versions of Windows with the built-in CMD command mklink. So, for example:

New-Item -Type HardLink `
         -Path 'C:\Build\New-myClientVM.ps1','C:\Build\New-myServerVM.ps1' `
         -Value 'C:\Build\New-myVM.ps1'

#Older OS Version:
cmd /c mklink /h C:\Build\New-myClientVM.ps1 C:\Build\New-myVM.ps1
cmd /c mklink /h C:\Build\New-myServerVM.ps1 C:\Build\New-myVM.ps1

I then use ($myInvocation.myCommand.Name -match "Client") to see if the filename I started the script with was New-myClientVM.ps1 , or one of the other names I have for this script.  ($myInvocation.myCommand.Name -match "Client") returns $True for New-myClientVM.ps1, but $False for filenames that don't include 'Client' in the filename.

Next, I set some basic variables used throughout the script. These are periodically tweaked as new builds become my default. Currently, they're set at:

$VMBase     = "$Path\$VMName"
$VHDSource  = $Source
$DVDBase    = $Source
$VHDBase    = "$VMBase\Virtual Hard Disks"
$SysVHD     = "$VMBase\Virtual Hard Disks\$VmName-System.vhdx"
$MachineBase= "$VMBase\Virtual Machines"
$ServerISO  = "$DVDBase\en_windows_server_2016_x64_dvd_9718492.iso"
$ClientISO  = "$DVDBase\en_windows_10_enterprise_version_1607_updated_jan_2017_x64_dvd_9714415.iso"
$ClientVHD  = "$Source\Generalized-client.vhdx"
if ($2012R2) { 
   $ServerVHD = "$Source\Generalized-2012R2.vhdx"
} else {
   $ServerVHD  = "$Source\Generalized-System.vhdx"
}

Nothing special there. Next, three functions to verify paths, etc. These are pretty basic Test-Path statements. If I need to create directories, I do. But if I don't find my source files where I expect them, or I find an already existing .vhdx where I'm not expecting one, then I use simple Throw statements to get me out and report the problem, since either of these failures will cause the script to fail, usually in an ugly way. ;)

Function Test-SourcePath () {
   if ($Client) {
      if ($dvd) {
         if (Test-Path $ClientISO) {
            Write-Verbose "Install ISO found at $ClientISO"
         } else {
            Throw "Client ISO not found at $ClientISO" 
         }
      } elseif (Test-Path $ClientVHD) { 
         Write-Verbose "Source VHD found at $ClientVHD"
      }
   } else {
      if ($dvd) {
         if (Test-Path $ServerISO) {
            Write-Verbose "Install ISO found at $ServerISO"
         } else {
            Throw "Server ISO not found at $ServerISO" 
         }
      } elseif (Test-Path $ServerVHD) { 
         Write-Verbose "Source VHD found at $ServerVHD"
      }
   }
}

if (! (Test-Path $VHDBase ) ) { 
   mkdir $VHDBase
}
if (! (Test-Path $MachineBase ) ) { 
   mkdir $MachineBase
}

Function Test-Clean () {
   If (Test-Path $VHDBase\*.vhdx ) {
      Throw "Found an existing VHD. Please clean up the target path and try again."
   }
}

You'll notice with these functions, and the ones that follow, everything builds on those original variables created at the top of the script, or as part of the script parameters. Yes, I need to keep those up to date. But there's only one place to make the changes.

Now, assuming I'm most likely going to be building from a sysprep'd VHD, I  copy that .vhdx file into my "Virtual Hard Disks" folder for this VM, changing the name as I do to reflect the new VM's name.

function Copy-myVhd () {
      if ( $DVD ) {
         Write-Verbose "DVD specified. Not copying source VHD to $SysVHD"
      } else { 
         if ( $Client ) { 
            Write-Verbose "Creating VM from Sysprep'd VHD base $ClientVHD"
            cp $ClientVHD $SysVHD 
         } else { 
         Write-Verbose "Creating VM from Sysprep'd VHD base $ServerVHD"
            cp $ServerVHD $SysVHD
         } 
      }
}

Now that we have all that setup work done, let's actually create the VM. We have to do this in two separate steps because Hyper-V doesn't give us a way to set the number of CPUs or configure some other stuff as part of the initial creation of the VM. We have to modify the VM after we first create it. Silly, but not all that hard to deal with in a script, though a real nuisance at the interactive command line.

Create-myVM {
if ($DVD ) { 
  New-VM -Name $VmName `
       -MemoryStartupBytes 1024MB `
       -BootDevice VHD `
       -Generation 2 `
       -SwitchName $vmSwitch `
       -NewVHDPath $SysVHD `
       -NewVHDSize 200GB `
       -Path $MachineBase
} else { 
  New-VM -Name $VmName `
       -MemoryStartupBytes 1024MB `
       -BootDevice VHD `
       -Generation 2 `
       -SwitchName $vmSwitch `
       -VHDPath $SysVHD `
       -Path $MachineBase
  }
}

And, we now have a VM. It's not quite what we want and need, yet, but we have a VM. One problem, I can't set the boot device to DVD, regardless of what the PowerShell help pages say, because I'm building Generation 2 virtual machines, and they don't allow you to specify 'CD' as the boot device during initial setup. So, we'll have to configure that, along with the other tweaks we need, as part of the next stage of the whole process. And for that, you'll have to wait until tomorrow, when I do Part 2 of New-myVM. :)