example.tfrecords not displaying on What-If dashboard

I've converted a keras model into tensorflow saved model using saved_model_builder.SavedModelBuilder(export_path)
to be able to use is on whatif.

I've started a serving docker container docker run -p 8500:8500 --mount type=bind,source=/var/www/whatif_testing/model_name,target=/models/model_name -e MODEL_NAME=model_name -t tensorflow/serving

JPEG image data is converted into serialized tfrecords file using the below code.

def convert_to_record(train_addrs, train_labels, destination, keyword="train"):
    # address to save the TFRecords file
    train_filename = os.path.join(destination, keyword+'.tfrecords')
    # open the TFRecords file
    writer = tf.python_io.TFRecordWriter(train_filename)
    for i in range(len(train_addrs)):
        # print how many images are saved every 1000 images
        if not i % 10:
            sys.stdout.write(
                '{} data: {}/{}\r'.format(keyword, i, len(train_addrs)))
            sys.stdout.flush()
        # Load the image
        img = cv2.imread(train_addrs[i])
        img = cv2.resize(img, shape, interpolation=cv2.INTER_CUBIC)
        img = img.astype(np.uint8)/255.0

        label = train_labels[i]
        # Create a feature
        feature = {keyword+'/label': tf.train.Feature(int64_list=tf.train.Int64List(value=[label])),
                   keyword+'/image': tf.train.Feature(bytes_list=tf.train.BytesList(value=[tf.compat.as_bytes(img.tostring())])) }
        # Create an example protocol buffer
        example = tf.train.Example(features=tf.train.Features(feature=feature))

        # Serialize to string and write on the file
        writer.write(example.SerializeToString())

    writer.close()
    sys.stdout.flush()

This leads to an error from the model server

status = StatusCode.INVALID_ARGUMENT
	details = "Expects arg[0] to be double but string is provided"
	debug_error_string = "{"created":"@1541100531.185075510",
       "description":"Error received from peer",
       "file":"src/core/lib/surface/call.cc",
        "file_line":1017,
       "grpc_message":"Expects arg[0] to be double but string is provided",
       "grpc_status":3}"

I'm trying to understand what is the correct format of input image, input label and signature_def_map of the model