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Syntax Basics

Overview of DSC Configurations

Desired State Configuration (DSC) in PowerShell uses configurations to define the desired state of a system. A configuration script describes resources (e.g., files, services, features) and their desired properties. When applied, DSC ensures the system matches the defined state.

Configuration Structure

A DSC configuration is defined using the Configuration keyword, followed by a name and a Node block specifying target systems. Resources are added using their resource names and property sets. 

Configuration <ConfigurationName> {
    Node <ComputerName> {
        <ResourceName> <ResourceInstanceName> {
            <Property1> = <Value1>
            <Property2> = <Value2>
            ...
        }
    }
}
  • <ConfigurationName>: The name of the configuration (e.g., EnsureIIS).
  • <ComputerName>: The target node (e.g., localhost or a remote computer).
  • <ResourceName>: The DSC resource (e.g., WindowsFeature, xRemoteFile).
  • <ResourceInstanceName>: A unique name for the resource instance.

Example: Ensuring IIS is Installed

This example ensures the IIS feature is installed on a local machine: 

Configuration EnsureIIS {
    Node localhost {
        WindowsFeature IIS {
            Name = "Web-Server"
            Ensure = "Present"
        }
    }
}

Explanation:
- The WindowsFeature resource ensures the "Web-Server" feature is installed.
- Ensure = "Present" specifies the desired state.

Applying the Configuration

After defining the configuration, compile it into a MOF file and apply it: 

# Generate the MOF file
EnsureIIS -OutputPath .\Output

# Apply the configuration
Start-DscConfiguration -ConfigurationName EnsureIIS -OutputPath .\Output -Wait -Verbose
  • -OutputPath: Specifies where the MOF file is saved.
  • -Wait: Blocks until the configuration completes.
  • -Verbose: Provides detailed output during application.

Key Takeaways

  • DSC configurations use the Configuration block to define resources and target nodes.
  • Resources are added with their specific property sets (e.g., WindowsFeature).
  • The Start-DscConfiguration cmdlet applies the configuration to the target system.
  • MOF files are generated during compilation and applied to enforce the desired state.