Pub/Sub Tutorial

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Note: This content applies only to Cloud Run functions—formerly Cloud Functions (2nd gen).

For the 1st gen version of this document, see the Pub/Sub tutorial (1st gen).

This simple tutorial demonstrates writing, deploying, and triggering an Event-Driven Cloud Run functions with a Pub/Sub trigger.

If you are new to Pub/Sub and want to learn more, see the Pub/Sub documentation, particularly managing topics and subscriptions. See Pub/Sub Triggers for an overview of working with Pub/Sub topics and subscriptions in Cloud Run functions.

If you're looking for code samples for using Pub/Sub itself, please visit the sample browser.

Note: You can also use HTTP-triggered functions to listen to Pub/Sub push subscriptions. Using an HTTP function enables a single function to subscribe to multiple Pub/Sub topics.

Objectives

• Write and deploy an Event-Driven Cloud Run function.
• Trigger the function by publishing a message to a Pub/Sub topic.

Costs

In this document, you use the following billable components of Google Cloud:

• Cloud Run functions
• Cloud Build
• Pub/Sub
• Artifact Registry
• Eventarc
• Cloud Logging

For details, see Cloud Run functions pricing.

To generate a cost estimate based on your projected usage, use the pricing calculator. New Google Cloud users might be eligible for a free trial.

Before you begin

1. 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.

2. In the Google Cloud console, on the project selector page, select or create a Google Cloud project.

   Note: If you don't plan to keep the resources that you create in this procedure, create a project instead of selecting an existing project. After you finish these steps, you can delete the project, removing all resources associated with the project.

   Go to project selector

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

4. Enable the Cloud Functions, Cloud Build, Artifact Registry, Eventarc, Logging, and Pub/Sub APIs.

   Enable the APIs

5. Install the Google Cloud CLI.

6. To initialize the gcloud CLI, run the following command:

   gcloud init

7. In the Google Cloud console, on the project selector page, select or create a Google Cloud project.

   Note: If you don't plan to keep the resources that you create in this procedure, create a project instead of selecting an existing project. After you finish these steps, you can delete the project, removing all resources associated with the project.

   Go to project selector

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

9. Enable the Cloud Functions, Cloud Build, Artifact Registry, Eventarc, Logging, and Pub/Sub APIs.

   Enable the APIs

10. Install the Google Cloud CLI.

11. To initialize the gcloud CLI, run the following command:

    gcloud init

If you already have the gcloud CLI installed, update it by running the following command:

gcloud components update

12. Prepare your development environment.

    Node.js

    Go to the Node.js setup guide

    Python

    Go to the Python setup guide

    Go

    Go to the Go setup guide

    Java

    Go to the Java setup guide

    C#

    Go to the .NET setup guide

    Ruby

    Go to the Ruby setup guide

    PHP

    Go to Using PHP on Google Cloud

Prerequisites

Create a Pub/Sub topic:

gcloud pubsub topics create YOUR_TOPIC_NAME

This is a mandatory step before you can deploy your function. In Cloud Run functions, Pub/Sub topics are not automatically created when you deploy a function.

Preparing the application

1. Clone the sample app repository to your local machine:

   Node.js

   git clone https://github.com/GoogleCloudPlatform/nodejs-docs-samples.git

   Alternatively, you can download the sample as a zip file and extract it.

   Python

   git clone https://github.com/GoogleCloudPlatform/python-docs-samples.git

   Alternatively, you can download the sample as a zip file and extract it.

   Go

   git clone https://github.com/GoogleCloudPlatform/golang-samples.git

   Alternatively, you can download the sample as a zip file and extract it.

   Java

   git clone https://github.com/GoogleCloudPlatform/java-docs-samples.git

   Alternatively, you can download the sample as a zip file and extract it.

   C#

   git clone https://github.com/GoogleCloudPlatform/dotnet-docs-samples.git

   Alternatively, you can download the sample as a zip file and extract it.

   Ruby

   git clone https://github.com/GoogleCloudPlatform/ruby-docs-samples.git

   Alternatively, you can download the sample as a zip file and extract it.

   PHP

   git clone https://github.com/GoogleCloudPlatform/php-docs-samples.git

   Alternatively, you can download the sample as a zip file and extract it.

2. Change to the directory that contains the Cloud Run functions sample code for accessing Pub/Sub:

   Node.js

   cd nodejs-docs-samples/functions/v2/helloPubSub/

   Python

   cd python-docs-samples/functions/v2/pubsub/

   Go

   cd golang-samples/functions/functionsv2/hellopubsub/

   Java

   cd java-docs-samples/functions/v2/pubsub/

   C#

   cd dotnet-docs-samples/functions/helloworld/HelloPubSub/

   Ruby

   cd ruby-docs-samples/functions/helloworld/pubsub/

   PHP

   cd php-docs-samples/functions/helloworld_pubsub/

3. Take a look at the sample code:

   Node.js

   const functions = require('@google-cloud/functions-framework');
   
   // Register a CloudEvent callback with the Functions Framework that will
   // be executed when the Pub/Sub trigger topic receives a message.
   functions.cloudEvent('helloPubSub', cloudEvent => {
     // The Pub/Sub message is passed as the CloudEvent's data payload.
     const base64name = cloudEvent.data.message.data;
   
     const name = base64name
       ? Buffer.from(base64name, 'base64').toString()
       : 'World';
   
     console.log(`Hello, ${name}!`);
   });

   Python

   import base64
   
   from cloudevents.http import CloudEvent
   import functions_framework
   
   
   # Triggered from a message on a Cloud Pub/Sub topic.
   @functions_framework.cloud_event
   def subscribe(cloud_event: CloudEvent) -> None:
       # Print out the data from Pub/Sub, to prove that it worked
       print(
           "Hello, " + base64.b64decode(cloud_event.data["message"]["data"]).decode() + "!"
       )
   
   

   Go

   
   // Package helloworld provides a set of Cloud Functions samples.
   package helloworld
   
   import (
   	"context"
   	"fmt"
   	"log"
   
   	"github.com/GoogleCloudPlatform/functions-framework-go/functions"
   	"github.com/cloudevents/sdk-go/v2/event"
   )
   
   func init() {
   	functions.CloudEvent("HelloPubSub", helloPubSub)
   }
   
   // MessagePublishedData contains the full Pub/Sub message
   // See the documentation for more details:
   // https://cloud.google.com/eventarc/docs/cloudevents#pubsub
   type MessagePublishedData struct {
   	Message PubSubMessage
   }
   
   // PubSubMessage is the payload of a Pub/Sub event.
   // See the documentation for more details:
   // https://cloud.google.com/pubsub/docs/reference/rest/v1/PubsubMessage
   type PubSubMessage struct {
   	Data []byte `json:"data"`
   }
   
   // helloPubSub consumes a CloudEvent message and extracts the Pub/Sub message.
   func helloPubSub(ctx context.Context, e event.Event) error {
   	var msg MessagePublishedData
   	if err := e.DataAs(&msg); err != nil {
   		return fmt.Errorf("event.DataAs: %w", err)
   	}
   
   	name := string(msg.Message.Data) // Automatically decoded from base64.
   	if name == "" {
   		name = "World"
   	}
   	log.Printf("Hello, %s!", name)
   	return nil
   }
   

   Java

   import com.google.cloud.functions.CloudEventsFunction;
   import com.google.gson.Gson;
   import functions.eventpojos.PubSubBody;
   import io.cloudevents.CloudEvent;
   import java.nio.charset.StandardCharsets;
   import java.util.Base64;
   import java.util.logging.Logger;
   
   public class SubscribeToTopic implements CloudEventsFunction {
     private static final Logger logger = Logger.getLogger(SubscribeToTopic.class.getName());
   
     @Override
     public void accept(CloudEvent event) {
       // The Pub/Sub message is passed as the CloudEvent's data payload.
       if (event.getData() != null) {
         // Extract Cloud Event data and convert to PubSubBody
         String cloudEventData = new String(event.getData().toBytes(), StandardCharsets.UTF_8);
         Gson gson = new Gson();
         PubSubBody body = gson.fromJson(cloudEventData, PubSubBody.class);
         // Retrieve and decode PubSub message data
         String encodedData = body.getMessage().getData();
         String decodedData =
             new String(Base64.getDecoder().decode(encodedData), StandardCharsets.UTF_8);
         logger.info("Hello, " + decodedData + "!");
       }
     }
   }

   C#

   using CloudNative.CloudEvents;
   using Google.Cloud.Functions.Framework;
   using Google.Events.Protobuf.Cloud.PubSub.V1;
   using Microsoft.Extensions.Logging;
   using System.Threading;
   using System.Threading.Tasks;
   
   namespace HelloPubSub;
   
   public class Function : ICloudEventFunction<MessagePublishedData>
   {
       private readonly ILogger _logger;
   
       public Function(ILogger<Function> logger) =>
           _logger = logger;
   
       public Task HandleAsync(CloudEvent cloudEvent, MessagePublishedData data, CancellationToken cancellationToken)
       {
           string nameFromMessage = data.Message?.TextData;
           string name = string.IsNullOrEmpty(nameFromMessage) ? "world" : nameFromMessage;
           _logger.LogInformation("Hello {name}", name);
           return Task.CompletedTask;
       }
   }

   Ruby

   require "functions_framework"
   require "base64"
   
   FunctionsFramework.cloud_event "hello_pubsub" do |event|
     # The event parameter is a CloudEvents::Event::V1 object.
     # See https://cloudevents.github.io/sdk-ruby/latest/CloudEvents/Event/V1.html
     name = Base64.decode64 event.data["message"]["data"] rescue "World"
   
     # A cloud_event function does not return a response, but you can log messages
     # or cause side effects such as sending additional events.
     logger.info "Hello, #{name}!"
   end

   PHP

   
   use CloudEvents\V1\CloudEventInterface;
   use Google\CloudFunctions\FunctionsFramework;
   
   // Register the function with Functions Framework.
   // This enables omitting the `FUNCTIONS_SIGNATURE_TYPE=cloudevent` environment
   // variable when deploying. The `FUNCTION_TARGET` environment variable should
   // match the first parameter.
   FunctionsFramework::cloudEvent('helloworldPubsub', 'helloworldPubsub');
   
   function helloworldPubsub(CloudEventInterface $event): void
   {
       $log = fopen(getenv('LOGGER_OUTPUT') ?: 'php://stderr', 'wb');
   
       $cloudEventData = $event->getData();
       $pubSubData = base64_decode($cloudEventData['message']['data']);
   
       $name = $pubSubData ? htmlspecialchars($pubSubData) : 'World';
       fwrite($log, "Hello, $name!" . PHP_EOL);
   }

Note: The Pub/Sub message's data is stored as a base64-encoded string in the data property of the PubsubMessage object. To extract this data, you may need to decode it as shown in the examples above.

Deploying the function

To deploy the function with a Pub/Sub trigger, run the following command in the directory that contains the sample code (or in the case of Java, the pom.xml file):

Node.js

gcloud functions deploy nodejs-pubsub-function \
--gen2 \
--runtime=nodejs22 \
--region=REGION \
--source=. \
--entry-point=helloPubSub \
--trigger-topic=YOUR_TOPIC_NAME

Use the --runtime flag to specify the runtime ID of a supported Node.js version to run your function.

Python

gcloud functions deploy python-pubsub-function \
--gen2 \
--runtime=python312 \
--region=REGION \
--source=. \
--entry-point=subscribe \
--trigger-topic=YOUR_TOPIC_NAME

Use the --runtime flag to specify the runtime ID of a supported Python version to run your function.

Go

gcloud functions deploy go-pubsub-function \
--gen2 \
--runtime=go122 \
--region=REGION \
--source=. \
--entry-point=HelloPubSub \
--trigger-topic=YOUR_TOPIC_NAME

Use the --runtime flag to specify the runtime ID of a supported Go version to run your function.

Java

gcloud functions deploy java-pubsub-function \
--gen2 \
--runtime=java21 \
--region=REGION \
--source=. \
--entry-point=functions.SubscribeToTopic \
--memory=512MB \
--trigger-topic=YOUR_TOPIC_NAME

Use the --runtime flag to specify the runtime ID of a supported Java version to run your function.

C#

gcloud functions deploy csharp-pubsub-function \
--gen2 \
--runtime=dotnet8 \
--region=REGION \
--source=. \
--entry-point=HelloPubSub.Function \
--trigger-topic=YOUR_TOPIC_NAME

Use the --runtime flag to specify the runtime ID of a supported .NET version to run your function.

Ruby

gcloud functions deploy ruby-pubsub-function \
--gen2 \
--runtime=ruby33 \
--region=REGION \
--source=. \
--entry-point=hello_pubsub \
--trigger-topic=YOUR_TOPIC_NAME

Use the --runtime flag to specify the runtime ID of a supported Ruby version to run your function.

PHP

gcloud functions deploy php-pubsub-function \
--gen2 \
--runtime=php83 \
--region=REGION \
--source=. \
--entry-point=helloworldPubsub \
--trigger-topic=YOUR_TOPIC_NAME

Use the --runtime flag to specify the runtime ID of a supported PHP version to run your function.

where YOUR_TOPIC_NAME is the name of the Pub/Sub topic to which the function will be subscribed.

You must create a topic before you run the deploy command, using either the Google Cloud console or the gcloud command-line tool. Unlike Cloud Run functions (1st gen), in Cloud Run functions, Pub/Sub topics are not automatically created when you deploy a function with a Pub/Sub trigger.

Note: Cloud Run functions automatically creates push subscriptions that forward messages from the specified topic to your function, even within a VPC Service Controls environment.

Triggering the function

To test the Pub/Sub function:

1. Publish a message to the topic:

   gcloud pubsub topics publish my-topic --message="Friend"
   

2. Read the function logs to see the result:

   gcloud functions logs read \
     --gen2 \
     --region=REGION \
     --limit=5 \
     FUNCTION_NAME
   

   Replace the following:

   • REGION is the name of the Google Cloud region where you deployed your function (for example, us-west1).
   • FUNCTION_NAME is the name you gave your function when you deployed it (for example, the Node.js function in this tutorial was deployed with the function name nodejs-pubsub-function).

   You should see logging output that includes your new "Friend" message.

   Note: Logs might take a few moments to appear. If you don't see them immediately, check again in a minute or two.

Clean up

To avoid incurring charges to your Google Cloud account for the resources used in this tutorial, either delete the project that contains the resources, or keep the project and delete the individual resources.

Deleting the project

The easiest way to eliminate billing is to delete the project that you created for the tutorial.

To delete the project:

Caution: Deleting a project has the following effects:

• Everything in the project is deleted. If you used an existing project for the tasks in this document, when you delete it, you also delete any other work you've done in the project.
• Custom project IDs are lost. When you created this project, you might have created a custom project ID that you want to use in the future. To preserve the URLs that use the project ID, such as an appspot.com URL, delete selected resources inside the project instead of deleting the whole project.

If you plan to explore multiple architectures, tutorials, or quickstarts, reusing projects can help you avoid exceeding project quota limits.

1. In the Google Cloud console, go to the Manage resources page.

   Go to Manage resources

2. In the project list, select the project that you want to delete, and then click Delete.
3. In the dialog, type the project ID, and then click Shut down to delete the project.

Deleting the Cloud Run function

Deleting Cloud Run functions does not remove any resources stored in Cloud Storage.

To delete the Cloud Run function you created in this tutorial, run the following command:

Node.js

gcloud functions delete nodejs-pubsub-function --gen2 --region REGION 

Python

gcloud functions delete python-pubsub-function --gen2 --region REGION 

Go

gcloud functions delete go-pubsub-function --gen2 --region REGION 

Java

gcloud functions delete java-pubsub-function --gen2 --region REGION 

C#

gcloud functions delete csharp-pubsub-function --gen2 --region REGION 

Ruby

gcloud functions delete ruby-pubsub-function --gen2 --region REGION 

PHP

gcloud functions delete php-pubsub-function --gen2 --region REGION 

You can also delete Cloud Run functions from the Google Cloud console.