Consider using an AD domain controller as a DNS server, for example. Most of the DNS zone is read and stored in memory, as is a good portion of the directory. Thus, memory on the machine will need to be plentiful to make it work well in both roles. Print services are more disk-intensive, which is not a typical problem for domain controllers. So, building a domain controller with print services on it would have some special considerations regarding RAID and disk controller cards.
Security issues do crop up from time to time. A RIS server, for example, has some special requirements and accesses that are not appropriate for other systems. DHCP can have some security concerns if put on DCs. Care must be taken when installing DNS on DCs, although this particular configuration is actually very desirable from a management standpoint. However, using a DC as a border DNS server (one that answers name resolution requests from Internet sources) is a bad idea. Putting IIS together on a DC is big security risk. Any application services should generally be on member servers as opposed to DCs.
This was first published in June 2003