PowerShell DSC In Vagrant

Adam Burns

I work mostly on Apple Mac OS X. I’ve also been writing a lot of Windows automation, and that means PowerShell DSC. PSDSC doesn’t work on OS X yet, and even once it does I won’t be able to test Windows-only resources. To test my configurations, I use Vagrant boxes. It took a little fiddling to get this set up, so I’m posting the code here in case you’re in the same situation.

This assumes you already have Vagrant working. I use the VirtualBox provider and I install everything with homebrew.

Today, Vagrant doesn’t have a native PowerShell DSC provisioner. I use the shell provisioner to run my Headless PSDSC script, which compiles and runs a configuration (headless_dsc.ps1):

Param(
    [Parameter(Mandatory=$false)]
    [String[]]
    $InputXmlFile
)
  
if ($InputXmlFile) {
    [XML]$Inputs = Get-Content -Path $InputXmlFile
}
  
$NodeData = @{
    NodeName = "localhost"
    Message = "This was hardcoded in the node data."
    Inputs = $Inputs.inputs
}
$ConfigurationData = @{AllNodes = @($NodeData)}
  
Configuration Headless {
    Import-DscResource -ModuleName PSDesiredStateConfiguration
  
    Node 'localhost' {
        Log Message {
            Message = $AllNodes.Message
        }
        if ($AllNodes.Inputs) {
            Log Input {
                Message = $AllNodes.Inputs.Message
            }
        }
    }
}
  
Headless -ConfigurationData $ConfigurationData
Start-DscConfiguration -Wait -Force -Verbose -Path .\Headless\

And here’s an input file to provide the example messages (input.xml):

<Inputs>
    <Message>This message came from the XML inputs.</Message>
</Inputs>

Now all you need is a Vagrantfile in the same directory:

Vagrant.configure("2") do |config|
  config.vm.box = "StefanScherer/windows_2019"
  config.vm.provision "file" do |file|
    file.source = "input.xml"
    file.destination = "input.xml"
  end
  config.vm.provision "shell" do |shell|
    shell.path = "headless_dsc.ps1"
    shell.args = ["-InputXmlFile", "input.xml"]
 
    # https://github.com/hashicorp/vagrant/issues/9138#issuecomment-444408251
    shell.privileged = false
  end
end

To create the box and run PSDSC:

vagrant up

If you’ve made changes and you want to recomplie and rerun the configuration:

vagrant provision

If you need to connect to the instance and run commands, check out vagrant rdp. You’ll need to install Remote Desktop from the App Store. There’s a funky bug: if Remote Desktop isn’t open, the first rdp command will open the app but won’t start a session. Just run it again and you’ll get a session window.

The provisioner uploads the script and XML file on every run even though the current directory is mounted as a synced folder on the box by default. I could have used an inline shell script to call the script directly via that sync, but sometimes I disable the sync for testing and it’s convenient for the provisioner to keep working.

Without shell.privileged = false, I got errors like this:

default: (10,8):UserId:
default: At line:72 char:1
default: + $folder.RegisterTaskDefinition($task_name, $task, 6, $username, $pass ...
default: + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
default:     + CategoryInfo          : OperationStopped: (:) [], ArgumentException
default:     + FullyQualifiedErrorId : System.ArgumentException
default: The system cannot find the file specified. (Exception from HRESULT: 0x80070002)
default: At line:74 char:1
default: + $registered_task = $folder.GetTask("\$task_name")
default: + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
default:     + CategoryInfo          : OperationStopped: (:) [], FileNotFoundException
default:     + FullyQualifiedErrorId : System.IO.FileNotFoundException
default: You cannot call a method on a null-valued expression.
default: At line:75 char:1
default: + $registered_task.Run($null) | Out-Null
default: + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
default:     + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
default:     + FullyQualifiedErrorId : InvokeMethodOnNull

The whole process froze and I had to ctrl+c twice to close it. There’s a bug. I left a link in a comment in the Vagrantfile that I recommend you keep in your code so this setting isn’t confusing later.

Happy automating!

Adam

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