Configuring a Desired State Configuration Client

Once we have our pull server in place and we're starting to create configurations, we need to set up our client nodes to be able to connect to the pull server and how we want the node to behave.

The High Points

Examining the Local Configuration Manager

The Desired State Configuration agent included in Windows Management Framework 4 (or natively on Server 2012 R2 / Windows 8.1) is exposed through the Local Configuration Manager.

PS> Get-DscLocalConfigurationManager

AllowModuleOverwrite           : False
CertificateID                  :
ConfigurationID                :
ConfigurationMode              : ApplyAndMonitor
ConfigurationModeFrequencyMins : 30
Credential                     :
DownloadManagerCustomData      :
DownloadManagerName            :
RebootNodeIfNeeded             : False
RefreshFrequencyMins           : 15
RefreshMode                    : PUSH
PSComputerName                 :

This is where we can configure the behavior of DSC for a particular node.  So, how do we configure it?  With DSC of course!

There is a configuration option LocalConfigurationManager that allows us to set values for the Local Configuration Manager.  A sample configuration looks something like this:

configuration LetsGetConfiguring
    param ($NodeId, $PullServer)    

        AllowModuleOverwrite = 'True'
        ConfigurationID = $NodeId
        ConfigurationModeFrequencyMins = 60 
        ConfigurationMode = 'ApplyAndAutoCorrect'
        RebootNodeIfNeeded = 'True'
        RefreshMode = 'PULL' 
        DownloadManagerName = 'WebDownloadManager'
        DownloadManagerCustomData = (@{ServerUrl = "https://$PullServer/psdscpullserver.svc"})

While this configuration looks similar to other configurations we might create, we need to apply it with a different command - Set-DscLocalConfigurationManager.

LetsGetConfiguring -NodeId 71defb7f-232b-4213-b289-08c3d424e162 -PullServer
Set-DscLocalConfigurationManager -path LetsGetConfiguring

The Local Configuration Manager offers a number of options, which we'll examine.


This one is pretty straight-forward and only impacts configurations where you are using a pull server.  If you allow module overwrite, newer versions of modules can replace existing modules.  If you don't enable this, you'll have to manually remove modules if you want a new copy to pull down.


CertficateID is a thumbprint of a certificate in the machine certificate store that will be used to decrypt any secrets present in the configuration.  DSC allows PSCredential objects to be marshaled through a MOF file, but requires them (without explicit authorization) to be encrypted. (There is another option as well, if you use the ConfigurationData feature, you can also supply the path to a certificate file to use - I'll be blogging that scenario later when I cover some more advanced scenarios.)


The ConfigurationID is a GUID which uniquely identifies what configuration a node should retrieve from a pull server.  If you haven't had to generate GUIDs before, a really easy way to do so is:

PS> [guid]::NewGuid().Guid


ConfigurationMode defines how the DSC client operates.  There are three valid values:

  • Apply
  • ApplyAndMonitor
  • ApplyAndAutoCorrect

(NOTE:  These descriptions of functionality are based on limited testing - the TechNet documentation is not up to date yet, but should be in the near future.)

Apply will apply the configuration once and after a successful run is logged, it will stop attempting to apply configuration or checking the configuration.  ApplyAndMonitor will apply a configuration as in Apply, but will continue to validate that a node is configured as described.  No corrective action will take place if there is configuration drift.  Finally, ApplyAndAutoCorrect is what most of us think of when looking at DSC as a configuration management tool.  This setting applies a configuration and checks it regularly.  If configuration drift is detected, the configuration manager will attempt to return the machine to the desired state (see how I worked the product name in there..).


This setting determines how frequently the configured method (the RefreshMode) will be run.  In the case of a pull server, this is how frequently the pull server will be checked for updated configurations.  The minimum value for this is 30.  This value needs to be a multiple of the RefreshFrequencyMins.  If it is not, the engine will treat it as if it was a multiple (rounded up).


The Credential supplied can be used for accessing remote resources.


DownloadManagerCustomData is a hashtable of values that is passed to the specified download manager.  In the case of a a pull server, the two possible keys are ServerUrl and AllowUnsecureConnection.


Here is where we specify which download manager to use.  DSC ships with two options, the WebDownloadManager (for the web-based pull server) and the DSCFileDownloadManager (for using an SMB share).


Here's another pretty self-explanatory setting.  DSC offers a method for resources to request a reboot.  If this setting is $true, then DSC will reboot the node when it is requested.  If it is set to $false, DSC will notify (via the verbose stream and the DSC log) that a reboot is required, but not actually reboot the node.


The RefreshFrequencyMins setting determines how often DSC runs an integrity check against the cached configuration value (or if the check falls on the ConfigurationModeFrequencyMins interval against the pull server if one is configured).  The minimum value for this setting is 15 minutes.


RefreshMode is either PUSH or PULL.  If you set the RefreshMode to PULL, you'll need to configure a download manager (via DownloadManagerName).

Next up, we'll look at how we can build custom resources.


  1. PowerShell on Linux exists to help Windows admins to help them transition away from Windows Server. But In a decade, when > 75% of workloads running on Azure are Linux, the tools used to manage those workloads will be designed for and meet the needs of the Linux administrator mindset. Linux administrators have a great set of mature tools and it isn't entirely clear why they'd want to transition to using PowerShell. Linux has won. The growth of Linux on Azure shows that. It's time for Azure to be a Linux First environment - and PowerShell on Linux doesn't really fit because it's primarily trying to graft a new and unproven Microsoft way of doing things onto successful practices and culture. Sure they can do it - but they'd be better off retraining everyone to "Think Linux".

    If Microsoft has (apparently) given up on Windows Server and understand that only a few legacy holdouts will want to run it in Azure in 10 years time (with the majority of workloads being Linux), they are wasting resources trying to reinvent how Linux administrators do things as a way of placating legacy Windows administrators. Legacy Windows administrators should bite the bullet and go "all-in" and adopt existing successful open source administration paradigms. The clock is ticking on their relevance and if they spend precious time investing in a nascent administration technology instead of fully transitioning to an open source mindset, they'll be less employable in future.

    PowerShell on Linux would be a neat idea if Windows Server had a future. It'll remain around in the same way that mainframes are still with us - but Microsoft has no interest in making a compelling case for organizations to choose their product over the free alternative. The future of Windows Server is the current reality of Windows Phone.

    • Thank you SO much for contributing your perspective! I do think - and I'm not a Microsoft fanboy per se - that you're misinformed, or at least under-informed. Time will tell, of course, but I suspect you've brought some personal bias to your viewpoint.

    • Interesting perspective. But I think you missed the point why Microsoft is actually open sourcing PowerShell. If you followed the talks that Jeffrey Snover did the last few years, it became clear that they want to be able to support heterogeneous environments. And for what I've seen now from Microsoft, and especially the PowerShell team, is that they don't have a hidden agenda. Microsoft is not the Microsoft anymore from let's say, 5-10 years ago.

      I agree with you, that there's a lot of Linux on Azure. But many, many companies I come are mainly Windows based infrastructures. Also guys that I know that work for other companies almost only see Windows based infra's.

      Yes, Linux has it's place in this world, but according for Microsoft there's no battle between Windows or Linux. They're citizens in IT which Microsoft wants to support best. And PowerShell is not a tool per se, it's meant to be a management framework. A framework that operates with built-in tools or in the case of Windows, the .NET framework.

      Windows Server has a big future, just look at the developments Microsoft is doing on Nano server.

    • Do you really think in 20 years well be dealing with "OS war" ?

      Do you think well see linux or windows in 20-30 years ? I dont.

      Do you think there is a loosing side or a winning side ? There are never winners in any war.

      From my POV, the shift towards lean kernels to accommodate the cloud, will get us eventually to a unified kernel of some sort getting the best of breed of all OSes, giving developers and IT the option to focus on the tools and the frameworks and less about the underlying layers.

      Running a business that creates OS is becoming very expensive. No one wants to be limited in the tools they want to use, thus the SQL on Linux is a huge huge thing in that sense and it will only get bigger with more such products going the same way. I have yet to see any major party offer anything similar things, coming from the Linux side because it takes money and effort very little companies have, so MS in that sense is helping transform the ecosystem again and its in a very good direction.

      Powershell on Linux exists so I, as a windows admin will have a lower barrier of entrance, if my boss decides one day to invest some our company assets on linux. If I can help my company get the right decisions that will save it money and achieve more and if that means going with a non MS way, guess what, I can still use my skills from the windows side without the hassle of the learning curve.

      For a long time I've been an advocate of learning both windows and Linux, no matter what I do mostly in my work time, as they are just tools to make the job, means to achieve a goal..they are not the goals themselves, and the movement to the cloud just emphasize it even more.

      I think your notion of what open source and free means is what's leading you in the line of thought and that's where I think you were wrong, imho.
      Not saying that my notion of what open source and free means is better, but its somewhat less biased. Nothing is free. Open source doesn't mean security (look at the horrible OpenSSL hole that's been there for two years and only recently been closed, or support-when-you-NEED it, that will always cost money, either by support contracts or having devs that know that specific language to deal with the bugs internaly (which by itself is even more limiting with the amount of languages and frameworks popping every second day).

      As for hidden agendas, you need to remember this is still a business. There's always money involved and business opportunities to be made. MS along they years was always good in creating those opportunities for itself and its partners and it continues to do so, the bottom line will be the tools. If you have ones that do the job for you, keep using them. If MS puts money and effort to create better tools with the community, who's the winner ? Everyone.

      I've seen this in the heated arguments on the PS repo the second it went public. The lack of broader vision some of the Linux base audience showed, the arrogance, the "Its mine, dont touch it" is somewhat alarming. I'm just happy to know that the sysadmins in 20 years, the ones born today well have a different starting point where they will choose the tools and be told what to use by old retiring sysadmins that are trying to hold to their precious seats instead of embracing change and supporting it in the evolving it world.

  2. If I have to copy files from installation folder to destination and I have to do exception handling because everything is automated, then how to do that? What all errors may arise and how to recognize and handle them? Please help.

  3. powershell ought to get the credit it deserves for enabling a developer to rapidly create rich output handling complex decisions based upon datasets gathered from various means and implementing a nearly infinite number of actions based on these. Simply put, it can be, and it is, much more than an admin tool, in the right hands.

  4. To start this is a thing of beauty in it's simplicity.
    Does anyone have experience with how much memory the results occupy and doing Get-job | Receive-Job at the end? If I run say a 1000 or 10,000 will this cause memory problems? I am thinking doing Get-Job -State Complete | Receive-Job & then |remove-job inside the loop (and logging it) would reduce the chance of running the host out of memory, or am I just over complicating it?

  5. a) Remoting
    The primary purpose of PS on *nix will be remoting to Win-Hosts, such as Bash on Windows vice versa.

    Due to the nature of *nix as document driven OS, an object based shell does not make that much sense. We're missing the API level. Jeffrey told us so, long ago.

    b) Religious affairs
    It's not about publishing the code (which is nevertheless great!).
    The GPL especially is the denial of the biz model that drives the revenue of Microsoft. So, indeed, haters will hate. Agree.

    But, in for a penny, in for a pound, PoSh is part of Windows which is an expensive, closed down product, increasingly incapacitating the user.

    c) The role of Community
    Sorry to say that, but the PS community is so much more than the few "Get-Expert -wellknown | Get-Random" MVPs. I know it's hard to see that inside the bubble.

    PoSh itself is gorgeous but - at the end - just a shell, such as Korn, C, Z and all the others.

    Far more important: the promise of a datacenter abstraction layer beyond the borders of specific vendors, automation and the refusal of a click UI.

    In this sense, publishing the underlying code is a statement which can't be exaggerated!

    Great Post, Don!

  6. Thanks, Don. This article saved me tons of frustration. I was writing a fairly simple script that would iterate through a list of servers and grab some WMI information. However, using Get-Content, I found that once the file went beyond some threshold, my script would no longer work properly. Implementing your method fixed my problem, and the script works perfectly.

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