Stream Pub/Sub Lite messages by using Dataflow

As an alternative to writing and running your own data processing programs, you can use Dataflow with the Pub/Sub Lite I/O connector for Apache Beam. Dataflow is a fully-managed service for transforming and enriching data in streaming (real-time) and batch modes with equal reliability and expressiveness. It reliably executes programs developed using the Apache Beam SDK, which has an extensible set of powerful stateful processing abstractions, and I/O connectors to other streaming and batch systems.

This quickstart shows you how to write an Apache Beam pipeline that will:

Read messages from Pub/Sub Lite
Window (or group) the messages by publish timestamp
Write the messages to Cloud Storage

It also shows you how to:

Submit your pipeline to run on Dataflow
Create a Dataflow Flex Template from your pipeline

This tutorial requires Maven, but it's also possible to convert the example project from Maven to Gradle. To learn more, see Optional: Convert from Maven to Gradle.

Before you begin

Sign in to your Google Cloud account. If you're new to Google Cloud, create an account to evaluate how our products perform in real-world scenarios. New customers also get $300 in free credits to run, test, and deploy workloads.

Install the Google Cloud CLI.

To initialize the gcloud CLI, run the following command:

gcloud init

Create or select a Google Cloud project.

Create a Google Cloud project:
```
gcloud projects create PROJECT_ID
```
Replace PROJECT_ID with a name for the Google Cloud project you are creating.
Select the Google Cloud project that you created:
```
gcloud config set project PROJECT_ID
```
Replace PROJECT_ID with your Google Cloud project name.

Make sure that billing is enabled for your Google Cloud project.

Enable the Pub/Sub Lite, Dataflow, Google Cloud Storage JSON API, and Cloud Logging APIs:

gcloud services enable pubsublite.googleapis.com  dataflow.googleapis.com  storage-api.googleapis.com  logging.googleapis.com

Set up authentication:

Create the service account:
```
gcloud iam service-accounts create SERVICE_ACCOUNT_NAME
```
Replace SERVICE_ACCOUNT_NAME with a name for the service account.
Grant roles to the service account. Run the following command once for each of the following IAM roles: roles/dataflow.worker, roles/storage.objectAdmin, roles/pubsublite.admin:
```
gcloud projects add-iam-policy-binding PROJECT_ID --member="serviceAccount:SERVICE_ACCOUNT_NAME@PROJECT_ID.iam.gserviceaccount.com" --role=ROLE
```
Replace the following:
- SERVICE_ACCOUNT_NAME: the name of the service account
- PROJECT_ID: the project ID where you created the service account
- ROLE: the role to grant
Note: The --role flag affects which resources the service account can access in your project. You can revoke these roles or grant additional roles later.
Grant the required role to the principal that will attach the service account to other resources.
```
gcloud iam service-accounts add-iam-policy-binding SERVICE_ACCOUNT_NAME@PROJECT_ID.iam.gserviceaccount.com --member="user:USER_EMAIL" --role=roles/iam.serviceAccountUser
```
Replace the following:
- SERVICE_ACCOUNT_NAME: the name of the service account
- PROJECT_ID: the project ID where you created the service account
- USER_EMAIL: the email address for a Google Account

Install the Google Cloud CLI.

To initialize the gcloud CLI, run the following command:

gcloud init

Create or select a Google Cloud project.

Create a Google Cloud project:
```
gcloud projects create PROJECT_ID
```
Replace PROJECT_ID with a name for the Google Cloud project you are creating.
Select the Google Cloud project that you created:
```
gcloud config set project PROJECT_ID
```
Replace PROJECT_ID with your Google Cloud project name.

Make sure that billing is enabled for your Google Cloud project.

Enable the Pub/Sub Lite, Dataflow, Google Cloud Storage JSON API, and Cloud Logging APIs:

gcloud services enable pubsublite.googleapis.com  dataflow.googleapis.com  storage-api.googleapis.com  logging.googleapis.com

Set up authentication:

Create the service account:
```
gcloud iam service-accounts create SERVICE_ACCOUNT_NAME
```
Replace SERVICE_ACCOUNT_NAME with a name for the service account.
Grant roles to the service account. Run the following command once for each of the following IAM roles: roles/dataflow.worker, roles/storage.objectAdmin, roles/pubsublite.admin:
```
gcloud projects add-iam-policy-binding PROJECT_ID --member="serviceAccount:SERVICE_ACCOUNT_NAME@PROJECT_ID.iam.gserviceaccount.com" --role=ROLE
```
Replace the following:
- SERVICE_ACCOUNT_NAME: the name of the service account
- PROJECT_ID: the project ID where you created the service account
- ROLE: the role to grant
Note: The --role flag affects which resources the service account can access in your project. You can revoke these roles or grant additional roles later.
Grant the required role to the principal that will attach the service account to other resources.
```
gcloud iam service-accounts add-iam-policy-binding SERVICE_ACCOUNT_NAME@PROJECT_ID.iam.gserviceaccount.com --member="user:USER_EMAIL" --role=roles/iam.serviceAccountUser
```
Replace the following:
- SERVICE_ACCOUNT_NAME: the name of the service account
- PROJECT_ID: the project ID where you created the service account
- USER_EMAIL: the email address for a Google Account

Create local authentication credentials for your user account:
```
gcloud auth application-default login
```

Set up your Pub/Sub Lite project

Create variables for your Cloud Storage bucket, project, and Dataflow region. Cloud Storage bucket names must be globally unique. The Dataflow region must be a valid region where you can run your job. For more information about regions and locations, see Dataflow locations.
```
export PROJECT_ID=$(gcloud config get-value project)
export SERVICE_ACCOUNT=SERVICE_ACCOUNT_NAME@PROJECT_ID.iam.gserviceaccount.com
export BUCKET=BUCKET_NAME
export DATAFLOW_REGION=DATAFLOW_REGION
```

Create a Cloud Storage bucket owned by this project:

   gcloud storage buckets create gs://$BUCKET

Create a Pub/Sub Lite zonal Lite topic and subscription

Create a zonal Lite Pub/Sub Lite topic and Lite subscription.

For the Lite location, choose a supported Pub/Sub Lite location. You must also specify a zone for the region. For example, us-central1-a.

export TOPIC=LITE_TOPIC_ID
export SUBSCRIPTION=LITE_SUBSCRIPTION_ID
export LITE_LOCATION=LITE_LOCATION
gcloud pubsub lite-topics create $TOPIC \
      --location=$LITE_LOCATION \
      --partitions=1 \
      --per-partition-bytes=30GiB
gcloud pubsub lite-subscriptions create $SUBSCRIPTION \
      --location=$LITE_LOCATION \
      --topic=$TOPIC \
      --starting-offset=beginning

Stream messages to Dataflow

Download the quickstart sample code

Clone the quickstart repository and navigate to the sample code directory.

git clone https://github.com/GoogleCloudPlatform/java-docs-samples.git
cd java-docs-samples/pubsublite/streaming-analytics

Sample code

This sample code uses Dataflow to:

Read messages from a Pub/Sub Lite subscription as an unbounded source.
Group messages based on their publish timestamps, using fixed time windows and the default trigger.
Write the grouped messages to files on Cloud Storage.

Java

Before running this sample, follow the Java setup instructions in Pub/Sub Lite Client Libraries.


import com.google.cloud.pubsublite.SubscriptionPath;
import com.google.cloud.pubsublite.proto.SequencedMessage;
import org.apache.beam.examples.common.WriteOneFilePerWindow;
import org.apache.beam.sdk.Pipeline;
import org.apache.beam.sdk.io.gcp.pubsublite.PubsubLiteIO;
import org.apache.beam.sdk.io.gcp.pubsublite.SubscriberOptions;
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.MapElements;
import org.apache.beam.sdk.transforms.windowing.FixedWindows;
import org.apache.beam.sdk.transforms.windowing.Window;
import org.apache.beam.sdk.values.TypeDescriptors;
import org.joda.time.Duration;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class PubsubliteToGcs {
  /*
   * Define your own configuration options. Add your arguments to be processed
   * by the command-line parser.
   */
  public interface PubsubliteToGcsOptions extends StreamingOptions {
    @Description("Your Pub/Sub Lite subscription.")
    @Required
    String getSubscription();

    void setSubscription(String value);

    @Description("Window size of output files in minutes.")
    @Default.Integer(1)
    Integer getWindowSize();

    void setWindowSize(Integer value);

    @Description("Filename prefix of output files.")
    @Required
    String getOutput();

    void setOutput(String value);
  }

  private static final Logger LOG = LoggerFactory.getLogger(PubsubliteToGcs.class);

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

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

    options.setStreaming(true);

    SubscriberOptions subscriberOptions =
        SubscriberOptions.newBuilder()
            .setSubscriptionPath(SubscriptionPath.parse(options.getSubscription()))
            .build();

    Pipeline pipeline = Pipeline.create(options);
    pipeline
        .apply("Read From Pub/Sub Lite", PubsubLiteIO.read(subscriberOptions))
        .apply(
            "Convert messages",
            MapElements.into(TypeDescriptors.strings())
                .via(
                    (SequencedMessage sequencedMessage) -> {
                      String data = sequencedMessage.getMessage().getData().toStringUtf8();
                      LOG.info("Received: " + data);
                      long publishTime = sequencedMessage.getPublishTime().getSeconds();
                      return data + "\t" + publishTime;
                    }))
        .apply(
            "Apply windowing function",
            Window
                // Group the elements using fixed-sized time intervals based on the element
                // timestamp (using the default event time trigger). The element timestamp
                // is the publish timestamp associated with a message.
                //
                // NOTE: If data is not being continuously ingested, such as with a batch or
                // intermittent publisher, the final window will never close as the watermark
                // will not advance. If this is a possibility with your pipeline, you should
                // add an additional processing time trigger to force window closure after
                // enough time has passed. See
                // https://beam.apache.org/documentation/programming-guide/#triggers
                // for more information.
                .<String>into(FixedWindows.of(Duration.standardMinutes(options.getWindowSize()))))
        .apply("Write elements to GCS", new WriteOneFilePerWindow(options.getOutput(), numShards));

    // Execute the pipeline. You may add `.waitUntilFinish()` to observe logs in your console, but
    // `waitUntilFinish()` will not work in Dataflow Flex Templates.
    pipeline.run();
  }
}

Start the Dataflow pipeline

To start the pipeline in Dataflow, run the following command:

mvn compile exec:java \
    -Dexec.mainClass=examples.PubsubliteToGcs \
    -Dexec.args=" \
        --subscription=projects/$PROJECT_ID/locations/$LITE_LOCATION/subscriptions/$SUBSCRIPTION \
        --output=gs://$BUCKET/samples/output \
        --windowSize=1 \
        --project=$PROJECT_ID \
        --region=$DATAFLOW_REGION \
        --tempLocation=gs://$BUCKET/temp \
        --runner=DataflowRunner \
        --serviceAccount=$SERVICE_ACCOUNT"

The preceding command launches a Dataflow job. Follow the link in the console output to access the job in the Dataflow monitoring console.

Observe job progress

Observe the job's progress in the Dataflow console.

Go to the Dataflow console

Open the job details view to see:

Job graph
Execution details
Job metrics

Publish some messages to your Lite topic.

gcloud pubsub lite-topics publish $TOPIC \
    --location=$LITE_LOCATION \
    --message="Hello World!"

You may have to wait a few minutes to see the messages in your Worker Logs.

Use the command below to check which files have been written out to Cloud Storage.

gcloud storage ls "gs://$BUCKET/samples/"

The output should look like the following:

 gs://$BUCKET/samples/output-19:41-19:42-0-of-1
 gs://$BUCKET/samples/output-19:47-19:48-0-of-1
 gs://$BUCKET/samples/output-19:48-19:49-0-of-1

Use the command below to look at the content in a file:

gcloud storage cat "gs://$BUCKET/samples/your-filename"

Optional: Create a Dataflow template

You can optionally create a custom Dataflow Flex Template based on your pipeline. Dataflow templates let you run jobs with different input parameters from Google Cloud console or the command line without the need to set up a full Java development environment.

Create a fat JAR that includes all the dependencies of your pipeline. You should see target/pubsublite-streaming-bundled-1.0.jar after the command has run.
```
mvn clean package -DskipTests=true
```

Provide names and locations for your template file and template container image.

export TEMPLATE_PATH="gs://$BUCKET/samples/your-template-file.json"
export TEMPLATE_IMAGE="gcr.io/$PROJECT_ID/your-template-image:latest"

Build a custom flex template. A required metadata.json file, which contains the necessary spec to run the job, has been provided with the example.

gcloud dataflow flex-template build $TEMPLATE_PATH \
    --image-gcr-path $TEMPLATE_IMAGE \
    --sdk-language "JAVA" \
    --flex-template-base-image "JAVA11" \
    --metadata-file "metadata.json" \
    --jar "target/pubsublite-streaming-bundled-1.0.jar" \
    --env FLEX_TEMPLATE_JAVA_MAIN_CLASS="examples.PubsubliteToGcs"

Run a job using the custom flex template.

Note: Pub/Sub Lite allows only one subscriber to pull messages from one partition. If your topic is configured to have only one partition and you use its subscription in more than one Dataflow jobs, only one job will receive messages.

Console

Create job from template.
Enter a Job name.
Enter your Dataflow region.
Choose your Custom Template.
Enter your template path.
Enter the required parameters.
Click Run job.

gcloud

gcloud dataflow flex-template run "pubsublite-to-gcs-`date +%Y%m%d`" \
     --template-file-gcs-location $TEMPLATE_PATH \
     --parameters subscription="projects/$PROJECT_ID/locations/$LITE_LOCATION/subscriptions/$SUBSCRIPTION" \
     --parameters output="gs://$BUCKET/samples/template-output" \
     --parameters windowSize=1 \
     --region $DATAFLOW_REGION \ 
     --serviceAccount=$SERVICE_ACCOUNT

Clean up

To avoid incurring charges to your Google Cloud account for the resources used on this page, delete the Google Cloud project with the resources.

In the Dataflow console, stop the job. Cancel the pipeline instead of draining it.

Delete the topic and subscription.

gcloud pubsub lite-topics delete $TOPIC
gcloud pubsub lite-subscriptions delete $SUBSCRIPTION

Delete the files created by the pipeline.

gcloud storage rm "gs://$BUCKET/samples/*" --recursive --continue-on-error
gcloud storage rm "gs://$BUCKET/temp/*" --recursive --continue-on-error

Delete the template image and the template file if they exist.

gcloud container images delete $TEMPLATE_IMAGE
gcloud storage rm $TEMPLATE_PATH

Remove the Cloud Storage bucket.

gcloud storage rm gs://$BUCKET --recursive

Delete the service account:

gcloud iam service-accounts delete SERVICE_ACCOUNT_EMAIL

Optional: Revoke the authentication credentials that you created, and delete the local credential file.
```
gcloud auth application-default revoke
```
Optional: Revoke credentials from the gcloud CLI.
```
gcloud auth revoke
```

What's next

Read more about Configuring Dataflow Flex Templates.
Understand Dataflow streaming pipelines.