This last Wednesday (10/11/17) I had the opportunity to share about PowerShell DSC at JAXSUGand I wanted to follow up and share a little more about what I was doing in my demo.

PowerShell Desired State Configuration (referred to as DSC from here on) is Microsoft’s new attempt to make server configuration easier and more stable for the Admin. DSC is a feature that is available in any version of Windows Server (or even Client) running PowerShell Version 4 or greater. One of the draws of DSC is that the configurations are human readable, declarative configurations, which allows ease of understanding for anyone reading the script. Additionally, these configurations provide a way to configure nodes in mass as well as offering a way to keep nodes from creeping out of its configuration.

Each node has a Local Configuration Manager(LCM), which is responsible for processing the configurations it receives. You can find out what your LCM by running Get-DSCLocalConfigurationManager in an Administrative PowerShell console. PowerShell is used to create the configurations as a .MOF file (or meta.mof if it is for the Local Configuration Manager). These files comply with the CIM (Common Information Model) which is an open standard and used by many different platforms. (Just a cool side note there are some people who use MOF files to control Linux systems and Networking devices, which have been made using PowerShell).

Each Configuration that is written may also need additional resources in order to extend the type of commands that can be given. By default PowerShell knows about 13 different resources for manipulating files and server settings. In order to Install SQL Server I needed to download and use the xSQLServer resource which may be found on GitHub

Below is a sample of the code for my LCM from my Demo with some comments

#These settings produce a $computer.meta.mof
# and are used to Setup the LocalConfiguration Manager
[DSCLocalConfigurationManager()]
Configuration LCM_Push
{
    #Paramater block allows this configuration to be used many times
    Param(
     [string[]]$ComputerName
    )
    #The Node keyword is used to determine
    #what the name of the meta.mof will be called
    Node $ComputerName
    {
         Settings
         {
         #These settings are only a few of all that are possible
         AllowModuleOverwrite = $True
         ConfigurationMode = 'Applyonly'
         RefreshMode = 'Push'
         RebootNodeIfNeeded = $True
         #The CertificateID allows you to use a Document Signing
         #certificate to Encrypt credentials within the .Mof file
         CertificateID = "56201A6926C2134876123409874C437E7E66BD"
         }
     }
}

If you would like to check out the script I used you can download it here: !(Push-SQL2017)[2017/10/Push-SQL2017.zip].

While my Demo only took about 15 minutes to preform the, the initial setup of the environment (Domain Controller, Authoring Host, and deployment Vm), the certificate server and certificates for encrypting the MOF (option in test, but necessary in prod), and the Configuration itself took many hours of testing and troubleshooting it has turned out to be a necessary tool as many requests come in to me for new instances or test instances and I now know I can reliably roll out a new version with a few clicks.