If you have Windows Server 2008 domain controllers and you're trying to build answer files for unattended installations of Active Directory Domain Services, this article should give you the information you need to perform the task successfully.
Performing an unattended installation using an answer file is not as hard as it sounds, and can be performed without any user interaction. Using the answer (or sometimes referred to as the unattend) file eliminates the need for an administrator to interact with the DCPROMO wizard, and is most important when using a server core machine to act as a DC. You can read more about Active Directory on Windows Server 2008 core installations on my "Installing Active Directory on Windows 2008 Server Core" article. You can also use the answer files to remove AD DS in unattended mode. Note that a similar article exists that describes the basics of the unattend file in Windows 2000/2003 – "How do I automatically upgrade a server to a domain controller during installation?"
One method of creating the unattend file is by manually copying a sample text and pasting it into a text file. You can read more about this process in the next section below. Another method of creating the file is by running the DCPROMO wizard on a different server, then, when finished, saving the configuration into a text file, and then pressing Cancel. You can read more about this method below.
Manually creating the unattend file
The unattend file can be manually created, and the fields in it properly populated. Here are some examples.
Note: Entries in the [DCInstall] section of the answer file indicate installation (or uninstallation) details. In this article I plan to discuss only the installation options, not the uninstall options. For more details on the process you can refer to TechNet KB article 947034 on this same topic.
The following list provides the common fields that are used for each operation. The default values are used if the option is not specified.