Ohai Chefs. Today’s release of Chef Client 11.16.0 marks the inclusion of PowerShell Desired State Configuration (DSC) support into Chef Client for Windows. DSC is a powerful configuration management platform built into PowerShell 4.0, and now you can use it with Chef!
To try it out, just configure a system with Chef Client 11.16.0 or later and target it with a recipe that uses the new `dsc_script` resource, which you can learn about on our documentation site.
Like Chef, DSC exposes *resources* to configure systems. The rest of this post gives details on how to use Chef’s new `dsc_script` resource to gain access to all of DSC’s resources from your recipes, and also discusses where we’re headed with DSC in the future.
The `dsc_script` resource allows cookbook authors to include DSC configurations in the form of PowerShell code in their Chef
recipes. This is not unlike the use of script code through Chef’s `powershell_script` or
`bash` resources. With DSC and `dsc_script`, however, you get a lot
more than just access to a scripting language. Here’s a simple example that uses
`dsc_script` in a Chef recipe to unzip (i.e. decompress) a file using DSC’s
`Archive` resource:
dsc\_script 'unzip\_powershell\_modules' do
code <<-EOH
Archive PSModules
Path = "$home/downloads/modules.zip"
Destination = "$env:programfiles/WindowsPowerShell/Modules"
}
EOH
end
The string supplied to the `code` attribute above is DSC (and therefore
PowerShell) code, which you can learn about at the DSC site. That PowerShell code specifies a “configuration” with DSC’s
`Archive` resource. Running this Chef recipe code will invoke
the DSC code and unzip the file located at `Path` to the directory location at
`Destination`.
Unlike, say, the use of a `bash` or `powershell_script` resource in Chef that
executes a decompression command like
`tar`, there is no need to write guard expressions (i.e. `not_if` / `only_if`)
in the recipe when using `dsc_script` in order to ensure idempotence — DSC
resources, like Chef resources, are intrinsically idempotent.
## DSC: A new universe of resources for Chef
PowerShell 4.0 ships with 12 built-in resources including `Archive`, most of
which are direct analogs of resources that already exist in Chef. But if you
install the recently released DSC Wave 6 resource kit from Microsoft, you suddenly have access to 80+ additional resources!
`xSQLHAGroup`, `xWebSite`, `xADUser`, `xDNSServer`, and `xVMHyperV` are some of
the suggestive resource names you’ll find if you install the resource kit and execute
`Get-DSCResource` in your PowerShell terminal. They do what their names imply
— configure web sites, high-availability database configurations, create
users in Active Directory, etc., all with Chef-like convergence. With
`dsc_script`, Chef users can build powerful cookbooks on top of DSC automation provided
by Microsoft and the PowerShell community.
## Re-using DSC configurations
While DSC itself is relatively new, ambitious users have already invested in their own libraries of DSC
scripts; these are consumed very much like Chef recipes. One could
integrate such a *”DSC recipe”* into a Chef recipe using `dsc_script` as follows:
dsc\_script 'CompanyWiki' do command '//infra01/configurations/wiki.ps1' flags AuthType: 'Windows', LogArchive: '//serverlogs/wiki' end
This will run the DSC configuration named `CompanyWiki` found in the
`wiki.ps1` script (“recipe”) given by the `command` attribute, and pass the parameters `AuthType` and `LogArchive` to the
configuration using `flags`.
## What’s next for DSC + Chef
Chef is not yet finished with DSC:
DSC accelerates our collective Chef efforts to automate *all the Windows things*. Now it’s up to us to start building.