PowerShell desired state configuration

In the previous section, we talked about ARM and ARM templates that define resources, but they are unable to design the way a VM looks inside, specify which software needs to be installed, and how the deployment should be done. This is why we need to have a look at VM extensions. VM extensions define what should be done after ARM deployment has finished. In general, the extension could be anything that's a script. The best practice is to use PowerShell and it's add-on called Desired State Configuration (DSC).

DSC defines quite similarly to ARM, how the software needs to be installed and configured. The great concept is, that it also monitors whether the desired state of a virtual machine is changing (for example, because an administrator uninstalls or re-configures a machine). If it does, it makes sure within minutes whether the original state will be fulfilled again and rolls back the actions to the desired state: