Just went the through the exercise of updating a small ROS project I worked on about 3 years ago from ROS indigo to the latest ROS melodic.
Original 2017 post: Turtlepi #7: Automatic Target Generation for the Turtlebot
The port was rather straight forward. The main issue was that Turtlebot 2 has yet to be included in the official melodic release. [1,2] Using the scripts put together as a result of community discussions  with minor modifications for my use case, helped a lot.
Working through old code is always enjoyable, and humbling. I was under the belief that I had shared a repository that was complete and working. Working through the 3 year old repository indicated otherwise.