Fabric configuration is currently implemented around a configuration library called [viper][viper]. Viper reads configuration from files, environment variables, and flags, and exposes an API that uses dot qualified keys to reference the configuration values (think System Properties on steroids).
When configuration is read from files, the segments of the configuration key are used to walk config file stanzas to the data. Values read from the configuration file can be overridden by setting an environment variable that