Dotnet core has this convention that __ (double underscore) can replace : so section__subsection environmental variable overwrites section:subsection .

When working with ASP.NET Core and Docker, it can be easy to get confused when trying to figure out who is setting what configuration variable and how. Especially if you are using one of the Visual Studio templates with Docker support.

Configuration is difficult, and confusing, and one of the first things to become a difficult thing to deal with once a project really starts to grow. Before you know it you have to store connection strings, api keys for multiple dependencies, logging settings and so on.

In classic ASP.NET and ASP.NET MVC, application settings and configuration were much easier. There was a global configuration file—web.config—and, within it, there was a section named appSettings that could receive flat name/value pairs of string data.