The configuration system in ASP.NET 5 has been completely overhauled and entire web.config/app.config mechanism has been thrown out in favor of a new pluggable system. The default configuration implementation uses a config.json file as storage, but the system is pluggable so other providers can be used instead as well as at the same time. For example, the default project template uses both config.json and environment variables, the latter of which override values in the .json file.
