Thursday, June 16, 2016

Desired State Configuration - Part 1

I have been diving into Powershell Desired State Configuration lately, as the technology is now a few years old and a little more mature, especially with the coming of Powershell 5. Many in the industry named this technology the technology that you should learn last year or the year before that already and not to mention that Microsoft keeps hammering on it that you should learn about it.

So what is Powershell DSC? In its core it is a configuration management platform. It allows for systems and applications to be installed and configured by means of a configuration document, and can manage configuration drift. Configuration management tools are not new, and have been around for a while with other tools like Puppet, Chef, Ansible, Salt and others.They serve the same purpose with varying features, but are mostly catered to Linux platforms. The same way that Powershell was an answer to having a proper commandline automation tool for Windows that supported its .Net and object oriented nature, DSC is Microsoft's answer to Configuration Management. But Microsoft went further by making DSC a platform that other tools use. So instead of competing against companies like Pupped and Chef, Microsoft has actively engaged with these companies so they could use the technology to better automatically configure Windows systems and applications.

Powershell and DSC inventor Jeffrey Snover describes DSC as captain Picard on the Starship Enterprise ordering Riker to go to that distant planet by saying "Make it so number one", and Riker executes that order: Picard desires something, and Riker "makes it so". DSC is basically the same thing inside your computer: With DSC, you desire something to be in a certain state through a configuration file and the local agent (called the Local Configuration Manager a.k.a. LCM) makes it so. This LCM is not all knowing in itself, but it uses things called DSC Resources to do the tasks you want it to do. These resources are now rapidly being developed by both Microsoft as well as the community around it, but if you can't find the thing you want to have configured, you can create them yourself. The main source for resources is the Powershell Gallery, and Powershell 5 has got the PowerShellGet module which now lets you install modules straight from this repository, just like you would use apt-get from a linux repository.

What makes DSC so cool?
  • You can deploy a system complete with applications and settings, nuke it and deploy the exact same machine (which makes devs happy because your dev matches your prod environment exactly)
  • Your OS/application is as you documented it in your configuration file, and configuration drift can be corrected by DSC
  • The DSC configuration is a Powershell based script, so you can use Powershell for variables and such, and do troubleshooting with it too
  • DSC can be used not only for Windows systems, but is slowly making its way to hardware devices too (e.g. Cisco Nexus)
  • There's linux support too, but as far as I've seen it, that's a bit of a work in progress. Cool nonetheless. 
  • Puppet/Chef/Salt/Ansible support the use of the DSC resources!
  • Windows Nano Server doesn't support Group Policies, but it supports DSC instead
There are more cool things about it, and DSC resources are added daily to make it even cooler. In another post I will go over the more technical details.

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