Cloud Pub/Sub Tutorial

This simple tutorial demonstrates writing, deploying, and triggering a Background Cloud Function with a Cloud 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 Google Cloud Pub/Sub Triggers for an overview of working with Pub/Sub topics and subscriptions in Cloud Functions.

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 a Background Cloud Function.
• Trigger the function by publishing a message to a Pub/Sub topic.

Costs

This tutorial uses billable components of Cloud Platform, including:

• Cloud Functions
• Pub/Sub

Use the Pricing Calculator to generate a cost estimate based on your projected usage.

New Cloud Platform users might be eligible for a free trial.

Before you begin

1. Sign in to your Google Account.

   If you don't already have one, sign up for a new account.

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

3. Verifica che la fatturazione sia attivata per il tuo progetto.

   scopri come attivare la fatturazione

4. Enable the Cloud Functions, Cloud Build, and Cloud Pub/Sub APIs.

   Enable the APIs

5. Install and initialize the Cloud SDK.
6. Update gcloud components:

   gcloud components update

7. 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

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.

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

   Node.js

   cd nodejs-docs-samples/functions/helloworld/

   Python

   cd python-docs-samples/functions/helloworld/

   Go

   cd golang-samples/functions/helloworld/

   Java

   cd java-docs-samples/functions/helloworld/hello-pubsub/

3. Take a look at the sample code:

   Node.js

   functions/helloworld/index.js

   View on GitHub

   /**
    * Background Cloud Function to be triggered by Pub/Sub.
    * This function is exported by index.js, and executed when
    * the trigger topic receives a message.
    *
    * @param {object} message The Pub/Sub message.
    * @param {object} context The event metadata.
    */
   exports.helloPubSub = (message, context) => {
     const name = message.data
       ? Buffer.from(message.data, 'base64').toString()
       : 'World';
   
     console.log(`Hello, ${name}!`);
   };

   Python

   functions/helloworld/main.py

   View on GitHub

   def hello_pubsub(event, context):
       """Background Cloud Function to be triggered by Pub/Sub.
       Args:
            event (dict):  The dictionary with data specific to this type of
            event. The `data` field contains the PubsubMessage message. The
            `attributes` field will contain custom attributes if there are any.
            context (google.cloud.functions.Context): The Cloud Functions event
            metadata. The `event_id` field contains the Pub/Sub message ID. The
            `timestamp` field contains the publish time.
       """
       import base64
   
       print("""This Function was triggered by messageId {} published at {}
       """.format(context.event_id, context.timestamp))
   
       if 'data' in event:
           name = base64.b64decode(event['data']).decode('utf-8')
       else:
           name = 'World'
       print('Hello {}!'.format(name))

   Go

   functions/helloworld/hello_pubsub.go

   View on GitHub

   
   // Package helloworld provides a set of Cloud Functions samples.
   package helloworld
   
   import (
   	"context"
   	"log"
   )
   
   // PubSubMessage is the payload of a Pub/Sub event.
   type PubSubMessage struct {
   	Data []byte `json:"data"`
   }
   
   // HelloPubSub consumes a Pub/Sub message.
   func HelloPubSub(ctx context.Context, m PubSubMessage) error {
   	name := string(m.Data) // Automatically decoded from base64.
   	if name == "" {
   		name = "World"
   	}
   	log.Printf("Hello, %s!", name)
   	return nil
   }
   

   Java

   functions/helloworld/hello-pubsub/src/main/java/functions/HelloPubSub.java

   View on GitHub

   
   import com.google.cloud.functions.BackgroundFunction;
   import com.google.cloud.functions.Context;
   import functions.eventpojos.PubSubMessage;
   import java.nio.charset.StandardCharsets;
   import java.util.Base64;
   import java.util.logging.Level;
   import java.util.logging.Logger;
   
   public class HelloPubSub implements BackgroundFunction<PubSubMessage> {
     private static final Logger logger = Logger.getLogger(HelloPubSub.class.getName());
   
     @Override
     public void accept(PubSubMessage message, Context context) {
       String name = "world";
       if (message != null && message.getData() != null) {
         name = new String(
             Base64.getDecoder().decode(message.getData().getBytes(StandardCharsets.UTF_8)),
             StandardCharsets.UTF_8);
       }
       logger.info(String.format("Hello %s!", name));
       return;
     }
   }

   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. The context parameter is described here.

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 helloPubSub \
--runtime nodejs10 \
--trigger-topic YOUR_TOPIC_NAME

You can use the following values for the --runtime flag to specify your preferred Node.js version:

• nodejs10
• nodejs12

Python

gcloud functions deploy hello_pubsub \
--runtime python37 \
--trigger-topic YOUR_TOPIC_NAME

You can use the following values for the --runtime flag to specify your preferred Python version:

• python37
• python38

Go

gcloud functions deploy HelloPubSub \
--runtime go111 \
--trigger-topic YOUR_TOPIC_NAME

You can use the following values for the --runtime flag to specify your preferred Go version:

• go111
• go113

Java

gcloud functions deploy java-pubsub-function \
--entry-point functions.HelloPubSub \
--runtime java11 \
--memory 512MB \
--trigger-topic YOUR_TOPIC_NAME

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

If YOUR_TOPIC_NAME doesn't already exist, this command creates it for you. You can also create a topic before you run the deploy command, using either the Cloud Console or the following gcloud command:

gcloud pubsub topics create YOUR_TOPIC_NAME

Triggering the function

1. Publish a message to your Pub/Sub topic. In this example, the message is a name that the function will include in a greeting:

   gcloud pubsub topics publish YOUR_TOPIC_NAME --message YOUR_NAME

   Replace YOUR_TOPIC_NAME with the name of your Pub/Sub topic, and YOUR_NAME with an arbitrary string.

2. Check the logs to be sure the executions have completed:

   gcloud functions logs read --limit 50
   

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

You can also publish a message to a Pub/Sub topic from within a function.

Cleaning up

To avoid incurring charges to your Google Cloud Platform account for the resources used in this tutorial:

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 this tutorial, 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 tutorials and quickstarts, reusing projects can help you avoid exceeding project quota limits.

1. In the Cloud Console, go to the Manage resources page.

   Go to the Manage resources page

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 Function

Deleting Cloud Functions does not remove any resources stored in Cloud Storage.

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

Node.js

gcloud functions delete helloPubSub 

Python

gcloud functions delete hello_pubsub 

Go

gcloud functions delete HelloPubSub 

Java

gcloud functions delete java-pubsub-function 

You can also delete Cloud Functions from the Google Cloud Console.