code: function(app) {
    if (process.env.POMELO_LOGGER !== 'off') {
      var env = app.get(Constants.RESERVED.ENV);
      var originPath = path.join(app.getBase(), Constants.FILEPATH.LOG);
      var presentPath = path.join(app.getBase(), Constants.FILEPATH.CONFIG_DIR, env, path.basename(Constants.FILEPATH.LOG));
      if(fs.existsSync(originPath)) {
        log.configure(app, originPath);
      } else if(fs.existsSync(presentPath)) {
        log.configure(app, presentPath);
      } else {
        logger.error('logger file path configuration is error.');
      }
    }
  }
docs: Configure custom logger.