logger

type Logger interface {
	// Debug log message at Debug level.
	Debug(format string, args ...interface{})
	// Info is like Debug, but logs at Info level.
	Info(format string, args ...interface{})
	// Warning is like Debug, but logs at Warning level.
	Warning(format string, args ...interface{})
	// Error is like Debug, but logs at Error level.
	Error(format string, args ...interface{})
}