code: function Client(options) {
    this.accessID = options.accessID;
    this.accessKey = options.accessKey;
    this.signatureMethod = options.signatureMethod || 'HmacSHA1';
    this.signatureVersion = options.signatureVersion || '1';
    this.APIVersion = options.APIVersion || '2013-05-10';
    this.APIHost = options.APIHost || 'http://ots.aliyuncs.com';
    // protocol: 'http:'
    // hostname: 'service.ots.aliyun.com'
    // port: undefined
    this.APIHostInfo = urlparse(this.APIHost);
    this.requestAgent = options.agent || null;
    this.requestTimeout = options.requestTimeout || 5000;
    var dnsCacheTime = options.dnsCacheTime || 10000;
    this.dns = CacheDNS.create({cacheTime: dnsCacheTime});
    this.vip = options.vip;
  }
docs: OTS Client.
  
  @param {Object} options
  - {String} accessID
  - {String} accessKey
  - {Number} [requestTimeout], default 5000ms.
  - {Agent} [http] request agent, default is `urllib.agent`.
  - {Number} [dnsCacheTime] dns cache time, default is `10000 ms`.
  - {String} [APIVersion] api version, default is '2013-05-10'.
  - {String} [APIHost] api host URL, default is 'http://service.ots.aliyun.com'.
  - {Object} [vip] OTS vip manager, only use for alibaba-inc. @suqian.yf
  @constructor