Relative DNS can be super useful. For example, you could have a project where, by convention, the app servers are just called as http://app/ http://app/ the db

Relative DNS can be super useful. For example, you could have a project where, by convention, the app servers are just called as http://app/ http://app/ the db servers are called as db etc. Saves lots of configuration effort. All you have to do is have a local DNS zone that keeps the traffic within its current setup. That way you don't even need separate app configuration for separate environments, and can transport an application and its configuration without changes into the next environment. (Sole exception: you likely want to inject different cryptographic keys to deal with (mutual) authentication).