We are preparing to deploy a new version of our application. The production environment will be two load balanced app servers connecting to two database servers (configured for mirroring). Now during testing in our office we use one app server and one db server and most of the authentication is done using our domain controller, we have discovered that domain authentication is nice and would like to keep that in production if possible.

When we go into production I am trying to figure out if it makes sense to have my two app servers be domain controllers so that authentication of the services to the SQL servers etc can use domain authentication.

What is the common practice in this sort of situation, should I use Active Directory, or is there a lightweight replacement? Is workgroup mode the accepted way? Is it foolish to have my app servers be domain controllers?