Write, Compile, and Apply a Configuration

Applies To: Windows PowerShell 4.0, Windows PowerShell 5.0

This exercise walks through creating and applying a Desired State Configuration (DSC) configuration from start to finish. In the following example, you will learn how to write and apply a very simple Configuration. The Configuration will ensure a "HelloWorld.txt" file exists on your local machine. If you delete the file, DSC will recreate it the next time it updates.

For an overview of what DSC is and how it works, see Desired State Configuration Overview for Developers.

Requirements

To run this example, you will need a computer running PowerShell 4.0 or later.

Write the configuration

A DSC Configuration is a special PowerShell function that defines how you want to configure one or more target computers (Nodes).

In the PowerShell ISE, or other PowerShell editor, type the following:

Configuration HelloWorld {

    # Import the module that contains the File resource.
    Import-DscResource -ModuleName PsDesiredStateConfiguration

    # The Node statement specifies which targets to compile MOF files for, when
    # this configuration is executed.
    Node 'localhost' {

        # The File resource can ensure the state of files, or copy them from a
        # source to a destination with persistent updates.
        File HelloWorld {
            DestinationPath = "C:\Temp\HelloWorld.txt"
            Ensure = "Present"
            Contents   = "Hello World from DSC!"
        }
    }
}

 Configuration HelloWorld {

  # Import the module that contains the File resource.
  Import-DscResource -ModuleName PsDesiredStateConfiguration
  Import-DscResource -ModuleName xWebAdministration

Save the file as "HelloWorld.ps1".

Defining a Configuration is like defining a Function. The Node block specifies the target node to be configured, in this case localhost.

The configuration calls one resources, the File resource. Resources do the work of ensuring that the target node is in the state defined by the configuration.

Compile the configuration

For a DSC configuration to be applied to a node, it must first be compiled into a MOF file. Running the configuration, like a function, will compile one .mof file for every Node defined by the Node block. In order to run the configuration, you need to dot source your HelloWorld.ps1 script into the current scope. For more information, see about_Scripts.

Dot source your HelloWorld.ps1 script by typing in the path where you stored it, after the . (dot, space). You may then, run your configuration by calling it like a function. You could also invoke the configuration function at the bottom of the script so that you don't need to dot-source.

. C:\Scripts\HelloWorld.ps1
HelloWorld

This generates the following output:

Directory: C:\Scripts\HelloWorld


Mode                LastWriteTime         Length Name
----                -------------         ------ ----
-a----        3/13/2017   5:20 PM           2746 localhost.mof

Apply the configuration

Now that you have the compiled MOF, you can apply the configuration to the target node (in this case, the local computer) by calling the Start-DscConfiguration cmdlet.

The Start-DscConfiguration cmdlet tells the Local Configuration Manager (LCM), the engine of DSC, to apply the configuration. The LCM does the work of calling the DSC resources to apply the configuration.

Use the code below to execute the Start-DSCConfiguration cmdlet. Specify the directory path where your localhost.mof is stored to the Path parameter. The Start-DSCConfiguration cmdlet looks through the directory specified for any <computername>.mof files. The Start-DSCConfiguration cmdlet attempts to apply each .mof file it finds to the computername specified by the filename ("localhost", "server01", "dc-02", etc.).

Start-DscConfiguration -Path C:\Scripts\HelloWorld -Verbose -Wait

Test the configuration

Once the Start-DSCConfiguration cmdlet is complete, you should see a HelloWorld.txt file in the location you specified. You can verify the contents with the Get-Content cmdlet.

You can also test the current status using Test-DSCConfiguration.

The output should be True if the Node is currently compliant with the applied Configuration.

Test-DSCConfiguration

True

Get-Content -Path C:\Temp\HelloWorld.txt

Hello World from DSC!

Re-applying the configuration

To see your configuration get applied again, you can remove the text file created by your Configuration. The use the Start-DSCConfiguration cmdlet with the -UseExisting parameter. The -UseExisting parameter instructs Start-DSCConfiguration to re-apply the "current.mof" file, which represents the most recently successfully applied configuration.

Remove-Item -Path C:\Temp\HelloWorld.txt

Next steps

• Find out more about DSC configurations at DSC configurations.
• See what DSC resources are available, and how to create custom DSC resources at DSC resources.
• Find DSC configurations and resources in the PowerShell Gallery.