Using Import-DSCResource

Import-DScResource is a dynamic keyword, which can only be used inside a Configuration script block. The Import-DSCResource keyword to import any resources needed in your Configuration. Resources under $pshome are imported automatically, but it is still considered best practice to explicitly import all resources used in your Configuration.

The syntax for Import-DSCResource is shown below. When specifying modules by name, it is a requirement to list each on a new line.

Import-DscResource [-Name <ResourceName(s)>] [-ModuleName <ModuleName>]
Parameter Description
-Name The DSC resource name(s) that you must import. If the module name is specified, the command searches for these DSC resources within this module; otherwise the command searches the DSC resources in all DSC resource paths. Wildcards are supported.
-ModuleName The module name, or module specification. If you specify resources to import from a module, the command will try to import only those resources. If you specify the module only, the command imports all the DSC resources in the module.
Import-DscResource -ModuleName xActiveDirectory;

Example: Use Import-DSCResource within a configuration

Configuration MSDSCConfiguration
{
    # Search for and imports Service, File, and Registry from the module PSDesiredStateConfiguration.
    Import-DSCResource -ModuleName PSDesiredStateConfiguration -Name Service, File, Registry
    
    # Search for and import Resource1 from the module that defines it.
    # If only –Name parameter is used then resources can belong to different PowerShell modules as well.
    # TimeZone resource is from the ComputerManagementDSC module which is not installed by default.
    # As a best practice, list each requirement on a different line if possible.  This makes reviewing
    # multiple changes in source control a bit easier.
    Import-DSCResource -Name File
    Import-DSCResource -Name TimeZone

    # Search for and import all DSC resources inside the module PSDesiredStateConfiguration.
    # When specifying the modulename parameter, it is a requirement to list each on a new line.
    Import-DSCResource -ModuleName PSDesiredStateConfiguration
    Import-DSCResource -ModuleName ComputerManagementDsc
...

Note

Specifying multiple values for Resource names and modules names in same command are not supported. It can have non-deterministic behavior about which resource to load from which module in case same resource exists in multiple modules. Below command will result in error during compilation.

Import-DscResource -Name UserConfigProvider*,TestLogger1 -ModuleName UserConfigProv,PsModuleForTestLogger

Things to consider when using only the Name parameter:

  • It is a resource-intensive operation depending on the number of modules installed on machine.
  • It will load the first resource found with the given name. In the case where there is more than one resource with same name installed, it could load the wrong resource.

The recommended usage is to specify –ModuleName with the -Name parameter, as described below.

This usage has the following benefits:

  • It reduces the performance impact by limiting the search scope for the specified resource.
  • It explicitly defines the module defining the resource, ensuring the correct resource is loaded.

Note

In PowerShell 5.0, DSC resources can have multiple versions, and versions can be installed on a computer side-by-side. This is implemented by having multiple versions of a resource module that are contained in the same module folder. For more information, see Using resources with multiple versions.

Intellisense with Import-DSCResource

When authoring the DSC configuration in ISE, PowerShell provides IntelliSence for resources and resource properties. Resource definitions under the $pshome module path are loaded automatically. When you import resources using the Import-DSCResource keyword, the specified resource definitions are added and Intellisense is expanded to include the imported resource's schema.

Resource Intellisense

Note

Beginning in PowerShell 5.0, tab completion was added to the ISE for DSC resources and their properties. For more information, see Resources.

When compiling the Configuration, PowerShell uses the imported resource definitions to validate all resource blocks in the configuration. Each resource block is validated, using the resource's schema definition, for the following rules.

  • Only properties defined in schema are used.
  • The data types for each property are correct.
  • Keys properties are specified.
  • No read-only property is used.
  • Validation on value maps types.

Consider the following configuration:

Configuration SchemaValidationInCorrectEnumValue
{
    # It is best practice to explicitly import all resources used in your Configuration.
    # This includes resources that are imported automatically, like WindowsFeature.
    Import-DSCResource -Name WindowsFeature
    Node localhost
    {
        WindowsFeature ROLE1
        {
            Name = “Telnet-Client”
            Ensure = “Invalid”
        }
    }
}

Compiling this Configuration results in an error.

PSDesiredStateConfiguration\WindowsFeature: At least one of the values ‘Invalid’ is not supported or valid for property ‘Ensure’ on class ‘WindowsFeature’. Please specify only supported values: Present, Absent.

Intellisense and schema validation allow you to catch more errors during parse and compilation time, avoiding complications at run time.

Note

Each DSC resource can have a name, and a FriendlyName defined by the resource's schema. Below are the first two lines of "MSFT_ServiceResource.shema.mof".

[ClassVersion("1.0.0"),FriendlyName("Service")]
class MSFT_ServiceResource : OMI_BaseResource

When using this resource in a Configuration, you can specify MSFT_ServiceResource or Service.

PowerShell v4 and v5 differences

There are multiple differences you see when authoring Configurations in PowerShell 4.0 vs. PowerShell 5.0 and later. This section will highlight the differences that you see relevant to this article.

Multiple Resource Versions

Installing and using multiple versions of resources side by side was not supported in PowerShell 4.0. If you notice issues importing resources into your Configuration, ensure that you only have one version of the resource installed.

In the image below, two versions of the xPSDesiredStateConfiguration module are installed.

Multiple Resource Versions Fixed

Copy the contents of your desired module version to the top level of the module directory.

Multiple Resource Versions Fixed

Resource location

When authoring and compiling Configurations, your resources can be stored in any directory specified by your PSModulePath. In PowerShell 4.0, the LCM requires all DSC resource modules to be stored under "Program Files\WindowsPowerShell\Modules" or $pshome\Modules. Beginning in PowerShell 5.0, this requirement was removed, and resource modules can be stored in any directory specified by PSModulePath.

See also