This was written on 8 November, 2019. Some of the issues mentioned below were discovered and resolved with the help of Microsoft support staff, and will hopefully be fixed in the near future.
The steps below are mostly taken from this tutorial, Deploying your Rails + PostgreSQL app on Microsoft Azure, but have also been influenced by these two other tutorials: Create a Ruby on Rails App in App Service on Linux and Build a Ruby and Postgres app in Azure App Service on Linux.
The descriptions of each step are my own personal understanding. I'm not an Azure expert, so they may not be correct 100% of the time.
Rails Version Note: The versions u