If you haven't heard..Apple is making serious changes to their Server application. Read more. It's removing many services that many never used in a directory service environment. However, for those that do use the services that have either been removed or will soon be departing, there is resource Apple has provided.
As of April 2018, Apple has released Version 1.1 Service Migration Guide. The guide provides essential information moving from existing services offered by macOS Server.
Also, Ben Goodstein's talk "The Sky is Falling! Or: Life After macOS Server" is another great source.