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Custom DSC resource for managing hosts file entries

Desired State Configuration is a new feature added to PowerShell 4.0 and Windows Server 2012 R2. DSC is a platform for deployment and management of configuration data. While there are several built-in DSC resources, it is possible to extend what we can achieve with DSC by creating custom resources.

In this article, I am introducing a new module I created to manage hosts file as a DSC resource. This custom DSC resource helps you add or remove entries to or from the hosts file in Windows Operating System.

Before I show you how you can use it, go ahead and download this custom DSC resource hosted on Github.

Once downloaded, you can copy the files to C:\Windows\System32\WindowsPowerShell\v1.0\Modules\PSDesiredStateConfiguration\PSProviders\HostsFile folder.

To start using the hosts file resource, we need to create a configuration document. A typical configuration document for managing hosts file is shown in the example below.

Configuration HostsFileExample {
    Node "SRV2-WS2012R2" {
        HostsFile HostsFileDemo {
            HostName = "testhost100"
            IPAddress = "10.10.10.100"
            Ensure = "Present"
        }
    }
}

HostsFileExample

The above example helps you add the hosts file entry on the remote computer named SRV2-WS2012R2. In the above example, setting Ensure=”Absent” will remove the host entry if it exists.

We can apply this configuration by saving the script file, dot-sourcing the script file, and then using Start-DSCConfiguration cmdlet to apply the configuration by providing the MOF file folder location as the value to –Path parameter.

PS C:\Demo> .\demo.ps1

 Directory: C:\Demo\HostsFileExample

Mode    LastWriteTime      Length    Name
----    -------------      ------    ----
-a---   8/18/2013 2:53 AM  948       SRV2-WS2012R2.mof

PS C:\Demo> Start-DscConfiguration -Path .\HostsFileExample -Wait -Verbose

Now, if we need to extend the above example to add different entries to multiple remote computers, we can do that by adding one more Node script block.

Configuration HostsFileExample {
    Node "SRV2-WS2012R2" {
        HostsFile HostsFileDemo {
            HostName = "testhost100"
            IPAddress = "10.10.10.100"
            Ensure = "Present"
        }
    }

    Node "SRV2-WS2012R2" {
        HostsFile HostsFileDemo {
            HostName = "testhost120"
            IPAddress = "10.10.10.120"
            Ensure = "Present"
        }
    }
}

HostsFileExample

When we dot-source the above script, it will create a MOF file for each node specified in the configuration document. We can, then, simply point Start-DSCConfiguration cmdlet to apply the configuration.

Now, what if we want to add multiple host entries per node in the configuration document? Simple! We add multiple HostsFile resource entries in a Node block. For example,

Configuration HostsFileExample {
    Node "SRV2-WS2012R2" {
        HostsFile HostsFileDemo {
            HostName = "testhost100"
            IPAddress = "10.10.10.100"
            Ensure = "Present"
        }
    }

    Node "SRV3-WS2012R2" {
        HostsFile HostsFileDemo {
            HostName = "testhost102"
            IPAddress = "10.10.10.102"
            Ensure = "Absent"
        }
   }

   Node "SRV1-WS2012R2" {
       HostsFile TestHost120 {
           HostName = "testhost120"
           IPAddress = "10.10.10.120"
           Ensure = "Absent"
       }

       HostsFile TestHost130 {
           HostName = "testhost130"
           IPAddress = "10.10.10.130"
           Ensure = "Present"
       }

   }
}

HostsFileExample

This is it. I have made this custom resource available on Github DSC repository created by Steven Murawski. Steve has a great guide on getting started with creating custom DSC resources which certainly was a starting point for the HostsFile resource. Feel free to log any issues or change requests. Also, fork it and update tosuit your requirements.

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