Pub/Sub to Cloud Storage using Dataflow

Stream Pub/Sub messages to Cloud Storage using Dataflow.

Documentation pages that include this code sample

To view the code sample used in context, see the following documentation:

Code sample

Java

Before trying this sample, follow the Java setup instructions in the Pub/Sub Quickstart Using Client Libraries. For more information, see the Pub/Sub Java API reference documentation.


import java.io.IOException;
import org.apache.beam.examples.common.WriteOneFilePerWindow;
import org.apache.beam.sdk.Pipeline;
import org.apache.beam.sdk.io.gcp.pubsub.PubsubIO;
import org.apache.beam.sdk.options.Default;
import org.apache.beam.sdk.options.Description;
import org.apache.beam.sdk.options.PipelineOptions;
import org.apache.beam.sdk.options.PipelineOptionsFactory;
import org.apache.beam.sdk.options.StreamingOptions;
import org.apache.beam.sdk.options.Validation.Required;
import org.apache.beam.sdk.transforms.windowing.FixedWindows;
import org.apache.beam.sdk.transforms.windowing.Window;
import org.joda.time.Duration;

public class PubSubToGcs {
  /*
   * Define your own configuration options. Add your own arguments to be processed
   * by the command-line parser, and specify default values for them.
   */
  public interface PubSubToGcsOptions extends PipelineOptions, StreamingOptions {
    @Description("The Cloud Pub/Sub topic to read from.")
    @Required
    String getInputTopic();

    void setInputTopic(String value);

    @Description("Output file's window size in number of minutes.")
    @Default.Integer(1)
    Integer getWindowSize();

    void setWindowSize(Integer value);

    @Description("Path of the output file including its filename prefix.")
    @Required
    String getOutput();

    void setOutput(String value);
  }

  public static void main(String[] args) throws IOException {
    // The maximum number of shards when writing output.
    int numShards = 1;

    PubSubToGcsOptions options =
        PipelineOptionsFactory.fromArgs(args).withValidation().as(PubSubToGcsOptions.class);

    options.setStreaming(true);

    Pipeline pipeline = Pipeline.create(options);

    pipeline
        // 1) Read string messages from a Pub/Sub topic.
        .apply("Read PubSub Messages", PubsubIO.readStrings().fromTopic(options.getInputTopic()))
        // 2) Group the messages into fixed-sized minute intervals.
        .apply(Window.into(FixedWindows.of(Duration.standardMinutes(options.getWindowSize()))))
        // 3) Write one file to GCS for every window of messages.
        .apply("Write Files to GCS", new WriteOneFilePerWindow(options.getOutput(), numShards));

    // Execute the pipeline and wait until it finishes running.
    pipeline.run().waitUntilFinish();
  }
}

Python

Before trying this sample, follow the Python setup instructions in the Pub/Sub Quickstart Using Client Libraries. For more information, see the Pub/Sub Python API reference documentation.

import argparse
import datetime
import json
import logging

import apache_beam as beam
from apache_beam.options.pipeline_options import PipelineOptions
import apache_beam.transforms.window as window


class GroupWindowsIntoBatches(beam.PTransform):
    """A composite transform that groups Pub/Sub messages based on publish
    time and outputs a list of dictionaries, where each contains one message
    and its publish timestamp.
    """

    def __init__(self, window_size):
        # Convert minutes into seconds.
        self.window_size = int(window_size * 60)

    def expand(self, pcoll):
        return (
            pcoll
            # Assigns window info to each Pub/Sub message based on its
            # publish timestamp.
            | "Window into Fixed Intervals"
            >> beam.WindowInto(window.FixedWindows(self.window_size))
            | "Add timestamps to messages" >> beam.ParDo(AddTimestamps())
            # Use a dummy key to group the elements in the same window.
            # Note that all the elements in one window must fit into memory
            # for this. If the windowed elements do not fit into memory,
            # please consider using `beam.util.BatchElements`.
            # https://beam.apache.org/releases/pydoc/current/apache_beam.transforms.util.html#apache_beam.transforms.util.BatchElements
            | "Add Dummy Key" >> beam.Map(lambda elem: (None, elem))
            | "Groupby" >> beam.GroupByKey()
            | "Abandon Dummy Key" >> beam.MapTuple(lambda _, val: val)
        )


class AddTimestamps(beam.DoFn):
    def process(self, element, publish_time=beam.DoFn.TimestampParam):
        """Processes each incoming windowed element by extracting the Pub/Sub
        message and its publish timestamp into a dictionary. `publish_time`
        defaults to the publish timestamp returned by the Pub/Sub server. It
        is bound to each element by Beam at runtime.
        """

        yield {
            "message_body": element.decode("utf-8"),
            "publish_time": datetime.datetime.utcfromtimestamp(
                float(publish_time)
            ).strftime("%Y-%m-%d %H:%M:%S.%f"),
        }


class WriteBatchesToGCS(beam.DoFn):
    def __init__(self, output_path):
        self.output_path = output_path

    def process(self, batch, window=beam.DoFn.WindowParam):
        """Write one batch per file to a Google Cloud Storage bucket. """

        ts_format = "%H:%M"
        window_start = window.start.to_utc_datetime().strftime(ts_format)
        window_end = window.end.to_utc_datetime().strftime(ts_format)
        filename = "-".join([self.output_path, window_start, window_end])

        with beam.io.gcp.gcsio.GcsIO().open(filename=filename, mode="w") as f:
            for element in batch:
                f.write("{}\n".format(json.dumps(element)).encode("utf-8"))


def run(input_topic, output_path, window_size=1.0, pipeline_args=None):
    # `save_main_session` is set to true because some DoFn's rely on
    # globally imported modules.
    pipeline_options = PipelineOptions(
        pipeline_args, streaming=True, save_main_session=True
    )

    with beam.Pipeline(options=pipeline_options) as pipeline:
        (
            pipeline
            | "Read PubSub Messages"
            >> beam.io.ReadFromPubSub(topic=input_topic)
            | "Window into" >> GroupWindowsIntoBatches(window_size)
            | "Write to GCS" >> beam.ParDo(WriteBatchesToGCS(output_path))
        )


if __name__ == "__main__":  # noqa
    logging.getLogger().setLevel(logging.INFO)

    parser = argparse.ArgumentParser()
    parser.add_argument(
        "--input_topic",
        help="The Cloud Pub/Sub topic to read from.\n"
        '"projects/<PROJECT_NAME>/topics/<TOPIC_NAME>".',
    )
    parser.add_argument(
        "--window_size",
        type=float,
        default=1.0,
        help="Output file's window size in number of minutes.",
    )
    parser.add_argument(
        "--output_path",
        help="GCS Path of the output file including filename prefix.",
    )
    known_args, pipeline_args = parser.parse_known_args()

    run(
        known_args.input_topic,
        known_args.output_path,
        known_args.window_size,
        pipeline_args,
    )