Originally posted on Nivlesh’s blog @ nivleshc.wordpress.com

Welcome back. In this blog we will continue with our new Active Directory Domain and use Desired State Configuration (DSC) to add a replica domain controller to it, for redundancy.

If you have not read the first part of this blog series, I would recommend doing that before continuing (even if you need a refresher). The first blog can be found at Create a new Active Directory Forest using Desired State Configuration

Whenever you create an Active Directory Domain, you should have, at a minimum, two domain controllers. This ensures that domain services are available even if one domain controller goes down.

To create a replica domain controller we will be using the xActiveDirectory and xPendingReboot experimental DSC modules. Download these from

https://gallery.technet.microsoft.com/scriptcenter/xActiveDirectory-f2d573f3

https://gallery.technet.microsoft.com/scriptcenter/xPendingReboot-PowerShell-b269f154

After downloading the zip files, extract the contents and place them in the PowerShell modules directory located at $env:ProgramFiles\WindowsPowerShell\Modules folder (unless you have changed your systemroot folder, this will be located at C:\ProgramFiles\WindowsPowerShell\Modules )

With the above done, open Windows PowerShell ISE and lets get started.

Paste the following into your PowerShell editor and save it using a filename of your choice (I have saved mine as CreateADReplicaDC.ps1 )

The above declares the parameters that need to be passed to the CreateADReplicaDC DSC configuration function ($DomainName , $Admincreds, $SafemodeAdminCreds). Some variables have also been declared ($RetryCount and $RetryIntervalSec). These will be used later within the configuration script.

Next, we have to import the experimental DSC modules that we have downloaded (unless the DSC modules are present out-of-the-box, they have to be imported so that they are available for use)

The $Admincreds parameter needs to be converted into a domain\username format. This is accomplished by using the following (the result is held in a variable called $DomainCreds)

Next, we need to tell DSC that the command has to be run on the local computer. This is done by the following line (localhost refers to the local computer)

Node localhost

As mentioned in the first blog, the DSC instructions are passed to the LocalConfigurationManager which carries out the commands. We need to tell the LocalConfigurationManager it should reboot the server if required, to continue with the configuration after a reboot, and to just apply the settings once (DSC can apply a setting and constantly monitor it to check that it has not been changed. If the setting is found to be changed, DSC can re-apply the setting. In our case we will not do this, we will apply the setting just once).

Next, we will install the Remote Server Administration Tools

Now, lets install Active Directory Domain Services Role

Before continuing on, we need to check if the Active Directory Domain that we are going to add the domain controller to is available. This is achieved by using the xWaitForADDomain function in the xActiveDirectory module.

Below is what we will use.

where
$DomainName is the name of the domain the domain controller will be joined to
$DomainCreds is the Administrator username and password for the domain (the username is in the format domain\username since we had converted this previously)

The DependsOn in the above code means that this section depends on the Active Directory Domain Services role to have been successfully installed.

So far, our script has successfully installed the Active Directory Domain Services role and has checked to ensure that the domain we will join the domain controller to is available.

So, lets proceed. We will now promote the virtual machine to a replica domain controller of our new Active Directory domain.

The above will only run after DscForestWait successfully signals that the Active Directory domain is available (denoted by DependsOn ). The SafeModeAdministratorPassword is set to the password that was provided in the parameters. The DatabasePath, LogPath and SysvolPath are all set to a location on C:\. This might not be suitable for everyone. For those that are uncomfortable with this, I would suggest to add another data disk to your virtual machine and point the Database, Log and Sysvol path to this new volume.

The only thing left now is to restart the server. So lets go ahead and do that

Keep in mind that the reboot will only happen if the domain controller was successfully added as a replica domain controller (this is due to the DependsOn).

That’s it. We now have a DSC configuration script that will add a replica domain controller to our Active Directory domain

The virtual machine that will be promoted to a replica domain controller needs to have the first domain controller’s ip address added to its dns settings and it also needs to have network connectivity to the first domain controller. These are required for the DSC configuration script to succeed.

The full DSC Configuration script is pasted below

If you would like to bootstrap the above to your Azure Resource Manager template, create a DSC extension and link it to the above DSC Configuration script (the script, together with the experimental DSC modules has to be packaged into a zip file and uploaded to a public location which ARM can access. I used GitHub for this)

One thing to note when bootstrapping is that after you create your first domain controller, you will need to inject its ip address into the dns settings of the virtual machine that will become your replica domain controller. This is required so that the virtual machine can locate the Active Directory domain.

I accomplished this by using the following lines of code in my ARM template, right after the Active Directory Domain had been created.

where

DC01 is the name of the first domain controller that was created in the new Active Directory domain
DC01NicIPAddress is the ip address of DC01
DC02 is the name of the virtual machine that will be added to the domain as a replica Domain Controller
DC02NicName is the name of the network card on DC02
DC02NicIPAddress is the ip address of DC02
DC02SubnetRef is a reference to the subnet DC02 is in
nicTemplateUri is the url of the ARM deployment template that will update the network interface settings for DC02 (it will inject the DNS settings). This file has to be uploaded to a location that ARM can access (for instance GitHub)

Below are the contents of the deployment template file that nicTemplateUri refers to

After the DNS settings have been updated, the following can be used to create a DSC extension to promote the virtual machine to a replica domain controller (it uses the DSC configuration script we had created earlier)

The variables used in the json file above are listed below (I have pointed repoLocation to my GitHub repository)

This concludes the DSC series for creating a new Active Directory domain and adding a replica domain controller to it.

Hope you all enjoyed this blog post.

Category:
Azure Infrastructure, Azure Platform, PowerShell
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Join the conversation! 3 Comments

  1. Hi Nivlesh,

    Great write up!
    Any advise on how to add a Read-only DC instead of a writable? I am asking for this because I searched a lot on MSDN regarding this, but the documentation is very difficult to navigate through.

    Regards,
    Ajinkya Apte

    Reply
  2. Hey Nivlesh,
    Firstly, great article and thanks for breaking it down so well.

    I’m having an issue with the xWaitForADDomain DscForestWait component where I’m unable to locate the existing domain (lab).
    On the server which I want to promote to a DC I can ping, resolve and browse (with creds) the domain and DC so I’m not sure why the DSC script cannot find the domain. Any tips on where to look or start troubleshooting?

    Reply
  3. this is good share The virtual machine that will be promoted to a replica domain controller needs to have the first domain controller’s ip address added to its dns settings and it also needs to have network connectivity to the first domain controller. These are required for the DSC configuration script to succeed.

    Reply

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