The new box will be brought up to netboot via PXE, which runs whichever automated installer your OS uses, including assigning IPs, partitioning the drives, etc.

The new box will be brought up to netboot via PXE, which runs whichever automated installer your OS uses, including assigning IPs, partitioning the drives, etc. The script then points to the proper configuration management system you use, which chooses the proper script for whatever the box is -- web frontend, database, etc -- and then finishes out the install. You're never a version behind, because your installer is maintained with every other bit of configuration. A good deployment system means new boxes are never out of date.