Executing PowerShell code

Some Windows maintenance tasks require the use of Windows Management Instrumentation (WMI), and PowerShell is the most useful way to access WMI methods. Puppet has a special module that can be used to execute arbitrary PowerShell code.

A common Windows maintenance tasks is to disable Windows drive indexing, because it can negatively impact disk performance on servers.

To disable drive indexing:
$drive = 'C:'

exec { 'disable-c-indexing':
   provider  => powershell,
   command   => "\$wmi_volume = Get-WmiObject -Class Win32_Volume -Filter 'DriveLetter=\"${drive}\"'; if (\$wmi_volume.IndexingEnabled -ne \$True) { return }; \$wmi_volume | Set-WmiInstance -Arguments @{IndexingEnabled = \$False}",
   unless    => "if ((Get-WmiObject -Class Win32_Volume -Filter 'DriveLetter=\"${drive}\"').IndexingEnabled) { exit 1 }",
}
You can see the results in your object editor window:
Object editor window showing that IndexingEnabled is set to FALSE.

Using the Windows built-in WBEMTest tool, running this manifest sets IndexingEnabled to FALSE, which is the desired behavior.

This exec sets a few important attributes:
  • The provider is configured to use PowerShell (which relies on the module).

  • The command contains inline PowerShell, and as such, must be escaped with PowerShell variables preceded with $ must be escaped as \$.

  • The unless attribute is set to ensure that Puppet behaves idempotently, a key aspect of using Puppet to manage resources. If the resource is already in the desired state, Puppet does not modify the resource state.