Viper is a complete configuration solution for Go applications including
12-Factor apps. It is designed to work within an application, and can handle all
types of configuration needs and formats. It supports:

- setting defaults
- reading from JSON, TOML, YAML, HCL, and Java properties config files
- live watching and re-reading of config files (optional)
- reading from environment variables
- reading from remote config systems (etcd or Consul), and watching changes
- reading from command line flags
- reading from buffer
- setting explicit values

Viper can be thought of as a registry for all of your applications configuration
needs.