docs: 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;
  }