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about_DesiredStateConfiguration

Updated: May 8, 2014

Applies To: Windows PowerShell 4.0, Windows PowerShell 5.0

TOPIC
    about_Desired_State_Configuration

SHORT DESCRIPTION
    Provides a brief introduction to the Windows 
    PowerShell Desired State Configuration (DSC) feature.
    
LONG DESCRIPTION
    DSC is a management platform in Windows PowerShell that enables deploying
    and managing configuration data for software services, and managing the
    environment in which these services run.

    DSC provides a set of Windows PowerShell language extensions,
    new cmdlets, and resources that you can use to declaratively specify
    how you want the state of your software environment to be configured. It
    also provides a means to maintain and manage existing configurations. 

    DSC is introduced in Windows PowerShell 4.0.

    For detailed information about DSC, see 
    "Windows PowerShell Desired State Configuration Overview" in the TechNet
    Library at http://go.microsoft.com/fwlink/?LinkId=311940.

DEVELOPING DSC RESOURCES WITH CLASSES
    Starting in Windows PowerShell 5.0, you can develop DSC resources by using
    classes. For more information, see about_Classes, and "Writing a custom
    DSC resource with PowerShell classes" on Microsoft TechNet
    (http://technet.microsoft.com/library/dn948461.aspx).
 
USING DSC
    To use DSC to configure your environment, first define a Windows 
    PowerShell script block using the Configuration keyword, followed by an
    identifier, which is in turn followed by the pair of curly braces delimiting
    the block. Inside the configuration block you can define node blocks that
    specify the desired configuration state for each node (computer) in the
    environment. A node block starts with the Node keyword, followed by the name
    of the target computer, which can be a variable. After the computer name, come
    the curly braces that delimit the node block. Inside the node block, you can
    define resource blocks to configure specific resources. A resource block starts
    with the type name of the resource, followed by the identifier you want to
    specify for that block, followed by the curly braces that delimit the block,
    as shown in the following example.
          
    Configuration MyWebConfig
    {
       # Parameters are optional
       param ($MachineName, $WebsiteFilePath)

       # A Configuration block can have one or more Node blocks
       Node $MachineName
       {
          # Next, specify one or more resource blocks
          # WindowsFeature is one of the resources you can use in a Node block
          # This example ensures the Web Server (IIS) role is installed
          WindowsFeature IIS
          {
             # To ensure that the role is not installed, set Ensure to "Absent"
              Ensure = "Present" 
              Name = "Web-Server" # Use the Name property from Get-WindowsFeature  
          }

          # You can use the File resource to create files and folders
          # "WebDirectory" is the name you want to use to refer to this instance
          File WebDirectory
          {
             Ensure = "Present"  # You can also set Ensure to "Absent“
             Type = "Directory“ # Default is “File”
             Recurse = $true
             SourcePath = $WebsiteFilePath
             DestinationPath = "C:\inetpub\wwwroot"
            
             # Ensure that the IIS block is successfully run first before
             # configuring this resource
             Requires = "[WindowsFeature]IIS"  # Use Requires for dependencies     
          }
       }
    }

    To create a configuration, invoke the Configuration block the same way you would
    invoke a Windows PowerShell function, passing in any expected parameters you may
    have defined (two in the example above). For example, in this case:

    MyWebConfig -MachineName "TestMachine" –WebsiteFilePath "\\filesrv\WebFiles" `
         -OutputPath "C:\Windows\system32\temp" # OutputPath is optional

    This generates a MOF file per node at the path you specify. These MOF files specify
    the desired configuration for each node. Next, use the following cmdlet to parse the
    configuration MOF files, send each node its corresponding configuration, and enact
    those configurations. Note that you do not need to create a separate MOF file for
    class-based DSC resources.

    Start-DscConfiguration –Verbose -Wait -Path "C:\Windows\system32\temp"

USING DSC TO MAINTAIN CONFIGURATION STATE
    With DSC, configuration is idempotent. This means that if you use DSC to enact the 
    same configuration more than once, the resulting configuration state will always
    be the same. Because of this, if you suspect that any nodes in your environment
    may have drifted from the desired state of configuration, you can enact the same
    DSC configuration again to bring them back to the desired state. You do not need 
    to modify the configuration script to address only those resources whose state has
    drifted from the desired state.
    
    The following example shows how you can verify whether the actual state of 
    configuration on a given node has drifted from the last DSC configuration enacted
    on the node. In this example we are checking the configuration of the local computer.

    $session = New-CimSession -ComputerName "localhost"
    Test-DscConfiguration -CimSession $session 

BUILT-IN DSC RESOURCES
    You can use the following built-in resources in your configuration scripts:

    Name                   Properties
    ----                   ----------
    File                   {DestinationPath, Attributes, Checksum, Contents...}
    Archive                {Destination, Path, Checksum, Credential...}
    Environment            {Name, DependsOn, Ensure, Path...}
    Group                  {GroupName, Credential, DependsOn, Description...}
    Log                    {Message, DependsOn, PsDscRunAsCredential}
    Package                {Name, Path, ProductId, Arguments...}
    Registry               {Key, ValueName, DependsOn, Ensure...}
    Script                 {GetScript, SetScript, TestScript, Credential...}
    Service                {Name, BuiltInAccount, Credential, Dependencies...}
    User                   {UserName, DependsOn, Description, Disabled...}
    WaitForAll             {NodeName, ResourceName, DependsOn, PsDscRunAsCredential...}
    WaitForAny             {NodeName, ResourceName, DependsOn, PsDscRunAsCredential...}
    WaitForSome            {NodeCount, NodeName, ResourceName, DependsOn...}
    WindowsFeature         {Name, Credential, DependsOn, Ensure...}
    WindowsOptionalFeature {Name, DependsOn, Ensure, LogLevel...}
    WindowsProcess         {Arguments, Path, Credential, DependsOn...}

    To get a list of available DSC resources on your system, run the
    Get-DscResource cmdlet.

    The example in this topic demonstrates how to use the File and WindowsFeature
    resources. To see all properties that you can use with a resource, insert the
    cursor in the resource keyword (for example, File) within your configuration
    script in Windows PowerShell ISE, hold down CTRL, and then press SPACEBAR.

FIND MORE RESOURCES
    You can download, install, and learn about many other available DSC resources that
    have been created by the PowerShell and DSC user community, and by Microsoft.
    Visit the PowerShell Gallery (https://www.powershellgallery.com/) to browse and learn
    about available DSC resources.

SEE ALSO
   "Windows PowerShell Desired State Configuration Overview"
   (http://go.microsoft.com/fwlink/?LinkId=311940)
   "Built-In Windows PowerShell Desired State Configuration Resources"
   (http://technet.microsoft.com/library/dn249921.aspx)
   "Build Custom Windows PowerShell Desired State Configuration Resources"
   (http://technet.microsoft.com/library/dn249927.aspx) 

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