node.js to upload image using multer shows undefined

Here I'm trying to upload files from 2 different file inputs, I'm able to upload it to the front-end but in the backend it remains undefined. Tried a couple of things but didn't work.

html:

<input type="file" name="file1" file-model = "file1"/>
<input type="file" name="file2" file-model = "file2"/>
<button  ng-click = "uploadFile()">UPLOAD FILES</button>

directive:

angular.module('myApp').directive('fileModel', ['$parse',
  function($parse) {
    return {
      restrict: 'A',
      link: function(scope, element, attrs) {
        var model = $parse(attrs.fileModel);
        var modelSetter = model.assign;

        element.bind('change', function() {
          scope.$apply(function() {
            modelSetter(scope, element[0].files[0]);
          });
        });
      }
    };
  }
])

service:

angular.module('myApp').service('fileUpload', ['$http',
  function($http) {
    this.uploadFileToUrl = function(file, uploadUrl) {
      var fd = new FormData();
      fd.append('file1', file);
      fd.append('file2', file);
      $http.post(uploadUrl, fd, {
        transformRequest: angular.identity,
        headers: {
          'Content-Type': undefined
        }
      })
    }
  }
]);

controller:

angular.module('myApp')
  .controller('ContactCtrl', ['$scope', 'fileUpload', '$http',
      function($scope, fileUpload, $http) {
        $scope.uploadFile = function() {
          var file1 = $scope.file1;
          var file2 = $scope.file2;
          console.log('file is ');
          console.dir(file1);
          console.dir(file2);

          var uploadUrl = '/upload';
          fileUpload.uploadFileToUrl({
            file1, file2
          }, uploadUrl);
        };

server:

function upload(req,res){
  console.log(req.files.file1);
}