Use WatchFilePattern to auto-update ML models in RunInference

The pipeline in this example uses a RunInference PTransform to run inference on images using TensorFlow models. It uses a side input PCollection that emits ModelMetadata to update the model.

Using side inputs, you can update your model (which is passed in a ModelHandler configuration object) in real-time, even while the Beam pipeline is still running. This can be done either by leveraging one of Beam’s provided patterns, such as the WatchFilePattern, or by configuring a custom side input PCollection that defines the logic for the model update.

For more information about side inputs, see the Side inputs section in the Apache Beam Programming Guide.

This example uses WatchFilePattern as a side input. WatchFilePattern is used to watch for the file updates matching the file_pattern based on timestamps. It emits the latest ModelMetadata, which is used in the RunInference PTransform to automatically update the ML model without stopping the Beam pipeline.

Set up the source

To read the image names, use a Pub/Sub topic as the source. The Pub/Sub topic emits a UTF-8 encoded model path that is used to read and preprocess images to run the inference.

Models for image segmentation

For the purpose of this example, use TensorFlow models saved in HDF5 format.

Pre-process images for inference

The Pub/Sub topic emits an image path. We need to read and preprocess the image to use it for RunInference. The read_image function is used to read the image for inference.

import io
from PIL import Image
from import FileSystems
import numpy
import tensorflow as tf

def read_image(image_file_name):
  with FileSystems().open(image_file_name, 'r') as file:
    data ='RGB')
  img = data.resize((224, 224))
  img = numpy.array(img) / 255.0
  img_tensor = tf.cast(tf.convert_to_tensor(img[...]), dtype=tf.float32)
  return img_tensor

Now, let’s jump into the pipeline code.

Pipeline steps:

  1. Get the image names from the Pub/Sub topic.
  2. Read and pre-process the images using the read_image function.
  3. Pass the images to the RunInference PTransform. RunInference takes model_handler and model_metadata_pcoll as input parameters.

For the model_handler, we use TFModelHandlerTensor.

from import TFModelHandlerTensor
# initialize TFModelHandlerTensor with a .h5 model saved in a directory accessible by the pipeline.
tf_model_handler = TFModelHandlerTensor(model_uri='gs://<your-bucket>/<model_path.h5>')

The model_metadata_pcoll is a side input PCollection to the RunInference PTransform. This side input is used to update the models in the model_handler without needing to stop the beam pipeline. We will use WatchFilePattern as side input to watch a glob pattern matching .h5 files.

model_metadata_pcoll expects a PCollection of ModelMetadata compatible with AsSingleton. Because the pipeline uses WatchFilePattern as side input, it will take care of windowing and wrapping the output into ModelMetadata.

After the pipeline starts processing data and when you see some outputs emitted from the RunInference PTransform, upload a .h5 TensorFlow model that matches the file_pattern to the Google Cloud Storage bucket. RunInference will update the model_uri of TFModelHandlerTensor using WatchFilePattern as a side input.

Note: Side input update frequency is non-deterministic and can have longer intervals between updates.

import apache_beam as beam
from import WatchFilePattern
from import RunInference
with beam.Pipeline() as pipeline:

  file_pattern = 'gs://<your-bucket>/*.h5'
  pubsub_topic = '<topic_emitting_image_names>'

  side_input_pcoll = (
    | "FilePatternUpdates" >> WatchFilePattern(file_pattern=file_pattern))

  images_pcoll = (
    | "ReadFromPubSub" >>
    | "DecodeBytes" >> beam.Map(lambda x: x.decode('utf-8'))
    | "PreProcessImage" >> beam.Map(read_image)

  inference_pcoll = (
    | "RunInference" >> RunInference(

Post-process the PredictionResult object

When the inference is complete, RunInference outputs a PredictionResult object that contains example, inference, and model_id fields. The model_id is used to identify which model is used for running the inference.

from import PredictionResult

class PostProcessor(beam.DoFn):
  Process the PredictionResult to get the predicted label and model id used for inference.
  def process(self, element: PredictionResult) -> typing.Iterable[str]:
    predicted_class = numpy.argmax(element.inference[0], axis=-1)
    labels_path = tf.keras.utils.get_file(
    imagenet_labels = numpy.array(open(labels_path).read().splitlines())
    predicted_class_name = imagenet_labels[predicted_class]
    return predicted_class_name.title(), element.model_id

post_processor_pcoll = (inference_pcoll | "PostProcessor" >> PostProcessor())

Run the pipeline

result =

Note: The model_name of the ModelMetaData object will be attached as prefix to the metrics calculated by the RunInference PTransform.

Final remarks

You can use this example as a pattern when using side inputs with the RunInference PTransform to auto-update the models without stopping the pipeline. You can see a similar example for PyTorch on GitHub.