Infrastructure as Code and DSC

Scripts describe steps. Declarative configuration describes the desired end state and lets a tool work out the steps — and it can be applied repeatedly with the same result (idempotence).

Idempotent scripts

Even without a framework, write scripts that check before they change:

function Set-DesiredFolder {
  [CmdletBinding(SupportsShouldProcess)]
  param([string]$Path)
  if (Test-Path -LiteralPath $Path) {
    "$Path already exists - no change"
  } elseif ($PSCmdlet.ShouldProcess($Path, 'Create folder')) {
    New-Item -ItemType Directory -Path $Path | Out-Null
    "$Path created"
  }
}

Set-DesiredFolder -Path logs
Set-DesiredFolder -Path logs

logs created
logs already exists - no change

Running it twice is safe: the second run changes nothing.

Desired State Configuration

DSC is PowerShell's declarative configuration platform. DSC v3 is a cross-platform command-line tool (dsc) that reads YAML or JSON configuration documents and uses resources — which can be written in PowerShell — to test and set state:

# web.dsc.yaml
$schema: https://aka.ms/dsc/schemas/v3/bundled/config/document.json
resources:
  - name: IIS feature
    type: PSDesiredStateConfiguration/WindowsFeature
    properties:
      Name: Web-Server
      Ensure: Present
  - name: App folder
    type: PSDesiredStateConfiguration/File
    properties:
      DestinationPath: C:\inetpub\app
      Type: Directory
      Ensure: Present

dsc config test --file web.dsc.yaml reports drift; dsc config set fixes it. Every resource implements Get, Test, and Set — exactly the idempotent pattern above. (Windows PowerShell 5.1 includes the older DSC v1 with Configuration blocks and MOF files, still found in many organizations.)

PowerShell alongside IaC tools

For cloud infrastructure, teams usually declare resources with Bicep, ARM templates, or Terraform, and use PowerShell around them: deploying templates (New-AzResourceGroupDeployment), preparing parameters, validating results, and handling the steps the declarative tools can't.