Chaganti - Windows PowerShell desired state configuration revealed : [everything you need to know about automating configuration management in Windows]

Appendix A

DSC Community Resources

For many system and IT administrators managing a mix of Windows and Linux/Unix-based environments, small or big, configuration management and preventing configuration drift is an essential task. Desired State Configuration (DSC) is built into the Windows operating system with the release of Windows Server 2012 R2, and Microsoft is working on enabling DSC for Linux or Unix environments. With these exciting changes in the IT data center management landscape, the community has been quick to adopt DSC and extend the resources to configure different elements in the IT ecosystem. With the official release of Windows Management Framework 4.0 and 5.0, there has been only a smaller subset of DSC resource modules. These resources are meant to cover some of the basic configurable entities in an operating system. We saw some of them in , it is very easy to convert that skill to writing a DSC resource module. Several enthusiasts from the PowerShell community have built such custom DSC resource modules for configuring different entities in their IT environment, and they are sharing their work with the rest of the community.

To support the community and extend the number of DSC resources, the Windows PowerShell team released several DSC resource kits. The total number of DSC resource modules in the DSC resource kit is staggering and is continuing to grow. There are not only resource modules but also helper modules that enable creating a template for custom DSC resources and debugging the configuration enactment process when using DSC.

In this appendix, we will look at an overview of some of the community DSC resources and a few DSC resource kit modules released by the Windows PowerShell team. In the earlier chapters, we did several configuration changes to build the DSC infrastructure manually, for example, creating an OData-based Pull service and so on. I mentioned in . The DSC diagnostics module in the resource kit makes it seamless to query event logs and get the right debugging information. We will look at these in detail in this appendix.

The DSC Community

The Windows PowerShell community, like any other active technical community, is very strong and has members who are experts in several other technologies, not just PowerShell. PowerShell is the glue. Each person in this community has a specific need when it comes to using PowerShell in their daily lives. With the release of Desired State Configuration (DSC), the community started to look at writing DSC resources and helping one another in doing more with DSC. For example, PowerShell.org began an initiative to host community-built custom DSC resources, and any that were updated to Microsoft provided resources as a GitHub repository. You can access it at https://github.com/PowerShellOrg/DSC . This is a public repository that accepts contributions from any community member. So, if you have your own custom DSC resources and want to share them with the rest of the community, this is the place where you can publish all that. Steven Murawski, a Windows PowerShell MVP and an expert in all things related to DSC, manages this repository. He is the author of all StackExchange DSC resources in this GitHub repository. There are many other DSC experts who help others get answers to their DSC-related questions, either through technical forums and/or their own blogs.

As I mentioned, the PowerShell.org repository has a mix of DSC resource modules and other helper modules, from both the community and the PowerShell team resource kits, so I wont provide details of the modules here. Instead, we will look at some of the modules in the official Microsoft DSC resource kit.

Windows PowerShell DSC Resource Kit

Soon after the release of WMF 4.0, the Windows PowerShell team started releasing several waves of DSC resource kits. At the time of this writing, wave 4 is the current release and has more than 50 PowerShell modules. These modules cover a breadth of features and applications, such as basic computer management, Azure virtual machines, Active Directory, SQL Availability Groups, Hyper-V Virtual Machine configurations, and so on. You can download these modules from the TechNet gallery at http://gallery.technet.microsoft.com/DSC-Resource-Kit-All-c449312d .

I encourage you to read the documentation accessible from the preceding link, to get a complete overview of the available modules in the resource kit. The modules in the resource kit are packaged as nested PowerShell modules. Therefore, once you download the zip file at the preceding link, you should extract it to the $env:ProgramFiles\WindowsPowerShell\Modules folder. Each resource kit module begins with the letter x, to indicate that it is an experimental resource module.

Note There is no official support for any of these modules. You can, however, report issues and seek help through Microsoft Connect and several other technical online forums.

There are two types of modules in this resource kit release. The first type is a PowerShell script module that complements the functionality of DSC. For example, the xDscDiagnostics , xDscResourceDesigner , and xPSDesiredStateConfiguration modules are PowerShell Script modules that are not DSC resources. You can see these modules in the output of the Get-Module cmdlet when the -ListAvailable switch parameter is used.

The second type of modules in the resource kit are DSC resource modules written as PowerShell script modules. We can use the Get-DscResource cmdlet to obtain a list of all these resource modules. This list is too exhaustive to fit in a single screenshot, but I recommend that you run this command and verify whether or not the DSC resource modules are listed.

It is impossible in this book to write about each of these modules. Therefore, I have chosen to showcase three modules that I use often when working with DSC. The following sections describe these modules and how some of the examples shown in earlier chapters can be executed in an easier way, with the help of these or custom DSC resources. Let us begin.

DSC Resource Designer

We have seen in what it takes to create a custom DSC resource. We have to create a schema Managed Object Format (MOF) with a specific syntax, a PowerShell module script that uses special semantics, and finally, a PowerShell module data file that describes the module. Each of these files has to be validated, so that they dont have any errors and dont fail when someone attempts to load them as DSC resources. For someone who has no knowledge of writing a schema MOF file, it will be hard to understand what qualifiers to use and so on. So, to make this process easy, and to create a skeleton for a custom DSC resource, the PowerShell team included what is called a DSC resource designer in the resource kit. What the resource designer cant help you with is the logic for the Get , Set , and Test-TargetResource functions of the DSC resource module.

You can access a list of cmdlets in this module by using the Get-Command cmdlet. This is shown in .

. Cmdlets in the DSC resource designer module

To understand how to use this module, and for demonstration purposes, let us create a skeleton for the HostsFile resource that we built in .

Defining Resource Properties

The HostsFile resource has only three attributes: IPAddress , HostName , and Ensure . The Ensure property is a value map that takes Present or Absent as valid values. Let us explore how to define these properties. We use the New-xDscResourceProperty cmdlet for this.