Pub/Sub to Cloud Storage using Dataflow

Stream Pub/Sub messages to Cloud Storage using Dataflow.

Explore further

For detailed documentation that includes this code sample, see the following:

• Stream messages from Pub/Sub by using Dataflow and Cloud Storage

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.

To authenticate to Pub/Sub, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

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.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 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.

To authenticate to Pub/Sub, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

import argparse
from datetime import datetime
import logging
import random

from apache_beam import (
    DoFn,
    GroupByKey,
    io,
    ParDo,
    Pipeline,
    PTransform,
    WindowInto,
    WithKeys,
)
from apache_beam.options.pipeline_options import PipelineOptions
from apache_beam.transforms.window import FixedWindows


class GroupMessagesByFixedWindows(PTransform):
    """A composite transform that groups Pub/Sub messages based on publish time
    and outputs a list of tuples, each containing a message and its publish time.
    """

    def __init__(self, window_size, num_shards=5):
        # Set window size to 60 seconds.
        self.window_size = int(window_size * 60)
        self.num_shards = num_shards

    def expand(self, pcoll):
        return (
            pcoll
            # Bind window info to each element using element timestamp (or publish time).
            | "Window into fixed intervals"
            >> WindowInto(FixedWindows(self.window_size))
            | "Add timestamp to windowed elements" >> ParDo(AddTimestamp())
            # Assign a random key to each windowed element based on the number of shards.
            | "Add key" >> WithKeys(lambda _: random.randint(0, self.num_shards - 1))
            # Group windowed elements by key. All the elements in the same window must fit
            # memory for this. If not, you need to use `beam.util.BatchElements`.
            | "Group by key" >> GroupByKey()
        )


class AddTimestamp(DoFn):
    def process(self, element, publish_time=DoFn.TimestampParam):
        """Processes each windowed element by extracting the message body and its
        publish time into a tuple.
        """
        yield (
            element.decode("utf-8"),
            datetime.utcfromtimestamp(float(publish_time)).strftime(
                "%Y-%m-%d %H:%M:%S.%f"
            ),
        )


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

    def process(self, key_value, window=DoFn.WindowParam):
        """Write messages in a batch to Google Cloud Storage."""

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

        with io.gcsio.GcsIO().open(filename=filename, mode="w") as f:
            for message_body, publish_time in batch:
                f.write(f"{message_body},{publish_time}\n".encode())


def run(input_topic, output_path, window_size=1.0, num_shards=5, pipeline_args=None):
    # Set `save_main_session` to True so DoFns can access globally imported modules.
    pipeline_options = PipelineOptions(
        pipeline_args, streaming=True, save_main_session=True
    )

    with Pipeline(options=pipeline_options) as pipeline:
        (
            pipeline
            # Because `timestamp_attribute` is unspecified in `ReadFromPubSub`, Beam
            # binds the publish time returned by the Pub/Sub server for each message
            # to the element's timestamp parameter, accessible via `DoFn.TimestampParam`.
            # https://beam.apache.org/releases/pydoc/current/apache_beam.io.gcp.pubsub.html#apache_beam.io.gcp.pubsub.ReadFromPubSub
            | "Read from Pub/Sub" >> io.ReadFromPubSub(topic=input_topic)
            | "Window into" >> GroupMessagesByFixedWindows(window_size, num_shards)
            | "Write to GCS" >> ParDo(WriteToGCS(output_path))
        )


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

    parser = argparse.ArgumentParser()
    parser.add_argument(
        "--input_topic",
        help="The Cloud Pub/Sub topic to read from."
        '"projects/<PROJECT_ID>/topics/<TOPIC_ID>".',
    )
    parser.add_argument(
        "--window_size",
        type=float,
        default=1.0,
        help="Output file's window size in minutes.",
    )
    parser.add_argument(
        "--output_path",
        help="Path of the output GCS file including the prefix.",
    )
    parser.add_argument(
        "--num_shards",
        type=int,
        default=5,
        help="Number of shards to use when writing windowed elements to GCS.",
    )
    known_args, pipeline_args = parser.parse_known_args()

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

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