Configuration files

First, we have a config directory in the root of our Phoenix application. This is where all of the application and web service configuration files will live. We typically have the config.exs, dev.exs, test.exs, prod.secret.exs, and prod.exs files by default with our Phoenix application. The first file, config.exs, is a file that stores generic configuration details that should be the same across all run-time environments for your application, whether they're testing, development, or production environments. The next few (dev.exs, test.exs, and prod.exs) are your environment-specific configuration files. Finally, we have our prod.secret.exs, which is auto-generated by Phoenix but not checked into source control by default. This file should never be checked into the source control for your application, as this is where sensitive information should live, such as API keys, secret keys, and database passwords. If this is ever checked into source control then it would be in the history of your application, which would be a pretty significant security concern for anyone having to maintain your Phoenix application!