An octal repr of permissions is supposed to be used here for working correctly.

pkg/logging/logger.go

@@ -20,7 +20,7 @@ type Logger struct {
 // NewLogger creates a Logger instance with given filename and
 // toStdout tells wether to write to Stdout as well or not.
 func NewLogger(path string, toStdout bool) (*Logger, error) {
-	f, err := os.OpenFile(path, os.O_WRONLY|os.O_APPEND|os.O_CREATE, os.ModeAppend)
+	f, err := os.OpenFile(path, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0660)
 	if err != nil {
 		return nil, errors.Wrap(err, "failed to open log file")
 	}