code: function(imageIdentifier, usePrimary) {
          if (usePrimary) {
              return this.options.hosts[0];
          }
  
          var dec = imageIdentifier.charCodeAt(imageIdentifier.length - 1);
  
          // If this is an old image identifier (32 character hex string),
          // maintain backwards compatibility
          if (imageIdentifier.match(/^[a-f0-9]{32}$/)) {
              dec = parseInt(imageIdentifier.substr(0, 2), 16);
          }
  
          return this.options.hosts[dec % this.options.hosts.length];
      }
docs: Get a predictable hostname for the given image identifier
  
  @param  {String} imageIdentifier
  @param  {Boolean} [usePrimary=false] Whether to use the primary host
  @return {String}