code: function initConnectionPool() {
  
    const setting = {
      host            : process.env.LIGHTMYSQL_HOST,
      port            : process.env.LIGHTMYSQL_PORT,
      user            : process.env.LIGHTMYSQL_USER,
      password        : process.env.LIGHTMYSQL_PASS,
      database        : process.env.APPNAME,
      connectionLimit : 10
    };
  
    console.log('MySQL name: ' + setting.database);
    console.log('MySQL host: ' + setting.host);
    console.log('MySQL port: ' + setting.port);
    console.log('MySQL user: ' + setting.user);
    console.log('MySQL pool: ' + setting.connectionLimit);
  
    return mysql.createPool(setting);
  }
docs: 初始化连接池
  @returns {Object}