Cloud Pub/Sub Tutorial (1st gen)

This simple tutorial demonstrates writing, deploying, and triggering an Event-Driven Cloud Run function 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.

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.

   Ruby

   git clone https://github.com/GoogleCloudPlatform/ruby-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/helloworld/

   Python

   cd python-docs-samples/functions/helloworld/

   Go

   cd golang-samples/functions/helloworld/

   Java

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

   Ruby

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

3. Take a look at the sample code:

   Node.js

   /**
    * 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

   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 `@type` field maps to
                            `type.googleapis.com/google.pubsub.v1.PubsubMessage`.
                           The `data` field maps to the PubsubMessage data
                           in a base64-encoded string. The `attributes` field maps
                           to the PubsubMessage attributes if any is present.
            context (google.cloud.functions.Context): Metadata of triggering event
                           including `event_id` which maps to the PubsubMessage
                           messageId, `timestamp` which maps to the PubsubMessage
                           publishTime, `event_type` which maps to
                           `google.pubsub.topic.publish`, and `resource` which is
                           a dictionary that describes the service API endpoint
                           pubsub.googleapis.com, the triggering topic's name, and
                           the triggering event type
                           `type.googleapis.com/google.pubsub.v1.PubsubMessage`.
       Returns:
           None. The output is written to Cloud Logging.
       """
       import base64
   
       print(
           """This Function was triggered by messageId {} published at {} to {}
       """.format(
               context.event_id, context.timestamp, context.resource["name"]
           )
       )
   
       if "data" in event:
           name = base64.b64decode(event["data"]).decode("utf-8")
       else:
           name = "World"
       print(f"Hello {name}!")
   
   

   Go

   
   // Package helloworld provides a set of Cloud Functions samples.
   package helloworld
   
   import (
   	"context"
   	"log"
   )
   
   // 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 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

   
   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;
     }
   }

   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

   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 nodejs22 \
--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 hello_pubsub \
--runtime python312 \
--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 HelloPubSub \
--runtime go121 \
--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 \
--entry-point functions.HelloPubSub \
--runtime java17 \
--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.

Ruby

gcloud functions deploy hello_pubsub --runtime ruby33 \
--trigger-topic YOUR_TOPIC_NAME

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

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 Google Cloud console or the following gcloud command:

gcloud pubsub topics create YOUR_TOPIC_NAME

Note: Cloud Run functions automatically creates push subscriptions that forward messages from the specified topic to your function.

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.