Trigger functions from Pub/Sub using Eventarc

Required roles

You or your administrator must grant the deployer account, the trigger identity, and optionally, the Pub/Sub service agent and the Cloud Storage service agent the following IAM roles.

Create a Pub/Sub topic

In Cloud Run, Pub/Sub topics are not automatically created when you deploy a function. Before deploying your function, publish a message to this Pub/Sub topic to trigger the function:

gcloudpubsubtopicscreateYOUR_TOPIC_NAME

Prepare the application

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

   Node.js

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

   Python

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

   Go

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

   Java

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

   .NET

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

   Ruby

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

   PHP

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

2. Change to the directory that contains the 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/
   

   .NET

   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

   constfunctions=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.
   constbase64name=cloudEvent.data.message.data;
   constname=base64name
   ?Buffer.from(base64name,'base64').toString()
   :'World';
   console.log(`Hello, ${name}!`);
   });

   Python

   importbase64
   fromcloudevents.httpimport CloudEvent
   importfunctions_framework
   # Triggered from a message on a Cloud Pub/Sub topic.
   @functions_framework.cloud_event
   defsubscribe(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.
   packagehelloworld
   import(
   "context"
   "fmt"
   "log"
   "github.com/GoogleCloudPlatform/functions-framework-go/functions"
   "github.com/cloudevents/sdk-go/v2/event"
   )
   funcinit(){
   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
   typeMessagePublishedDatastruct{
   MessagePubSubMessage
   }
   // 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
   typePubSubMessagestruct{
   Data[]byte`json:"data"`
   }
   // helloPubSub consumes a CloudEvent message and extracts the Pub/Sub message.
   funchelloPubSub(ctxcontext.Context,eevent.Event)error{
   varmsgMessagePublishedData
   iferr:=e.DataAs(&msg);err!=nil{
   returnfmt.Errorf("event.DataAs: %w",err)
   }
   name:=string(msg.Message.Data)// Automatically decoded from base64.
   ifname==""{
   name="World"
   }
   log.Printf("Hello, %s!",name)
   returnnil
   }
   

   Java

   importcom.google.cloud.functions.CloudEventsFunction;
   importcom.google.gson.Gson;
   importfunctions.eventpojos.PubSubBody;
   importio.cloudevents.CloudEvent;
   importjava.nio.charset.StandardCharsets;
   importjava.util.Base64;
   importjava.util.logging.Logger;
   publicclass SubscribeToTopicimplementsCloudEventsFunction{
   privatestaticfinalLoggerlogger=Logger.getLogger(SubscribeToTopic.class.getName());
   @Override
   publicvoidaccept(CloudEventevent){
   // The Pub/Sub message is passed as the CloudEvent's data payload.
   if(event.getData()!=null){
   // Extract Cloud Event data and convert to PubSubBody
   StringcloudEventData=newString(event.getData().toBytes(),StandardCharsets.UTF_8);
   Gsongson=newGson();
   PubSubBodybody=gson.fromJson(cloudEventData,PubSubBody.class);
   // Retrieve and decode PubSub message data
   StringencodedData=body.getMessage().getData();
   StringdecodedData=
   newString(Base64.getDecoder().decode(encodedData),StandardCharsets.UTF_8);
   logger.info("Hello, "+decodedData+"!");
   }
   }
   }

   .NET

   usingCloudNative.CloudEvents;
   usingGoogle.Cloud.Functions.Framework;
   usingGoogle.Events.Protobuf.Cloud.PubSub.V1;
   usingMicrosoft.Extensions.Logging;
   usingSystem.Threading;
   usingSystem.Threading.Tasks;
   namespaceHelloPubSub;
   publicclassFunction:ICloudEventFunction<MessagePublishedData>
   {
   privatereadonlyILogger_logger;
   publicFunction(ILogger<Function>logger)=>
   _logger=logger;
   publicTaskHandleAsync(CloudEventcloudEvent,MessagePublishedDatadata,CancellationTokencancellationToken)
   {
   stringnameFromMessage=data.Message?.TextData;
   stringname=string.IsNullOrEmpty(nameFromMessage)?"world":nameFromMessage;
   _logger.LogInformation("Hello {name}",name);
   returnTask.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.decode64event.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);
   }

Deploy an event-driven function

To deploy the function, run the following command in the directory that contains the sample code:

 gcloud run deploy FUNCTION \
 --source . \
 --function helloPubSub \
 --base-image BASE_IMAGE \

 gcloud run deploy FUNCTION \
 --source . \
 --function subscribe \
 --base-image BASE_IMAGE \

 gcloud run deploy FUNCTION \
 --source . \
 --function HelloPubSub \
 --base-image BASE_IMAGE \

 gcloud run deploy FUNCTION \
 --source . \
 --function functions.SubscribeToTopic \
 --base-image BASE_IMAGE \

 gcloud run deploy FUNCTION \
 --source . \
 --function HelloPubSub.Function \
 --base-image BASE_IMAGE \

 gcloud run deploy FUNCTION \
 --source . \
 --function hello_pubsub \
 --base-image BASE_IMAGE \

 gcloud run deploy FUNCTION \
 --source . \
 --function helloworldPubsub \
 --base-image BASE_IMAGE \

If you are prompted to create a repository in the specified region, respond by pressing y. When the deployment is complete, the Google Cloud CLI displays a URL where the service is running.

Create an Eventarc trigger

To deploy the function with a Pub/Sub trigger, run the following command in the directory that contains the sample code:

1. Create an Eventarc Pub/Sub trigger:

   gcloudeventarctriggerscreateTRIGGER_NAME\
   --location=${REGION}\
   --destination-run-service=FUNCTION\
   --destination-run-region=${REGION}\
   --event-filters="type=google.cloud.pubsub.topic.v1.messagePublished"\
   --service-account=PROJECT_NUMBER-compute@developer.gserviceaccount.com

   Replace:

   • TRIGGER_NAME with the name for your trigger.
   • FUNCTION with the name of your function.
   • PROJECT_NUMBER with your Google Cloud project number.

   Note that when creating an Eventarc trigger for the first time in a Google Cloud project, there might be a delay in provisioning the Eventarc service agent. This issue can usually be resolved by attempting to create the trigger again. For more information, see Permission denied errors.

2. Confirm that the trigger was successfully created. Note that although your trigger is created immediately, it can take up to two minutes for a trigger to be fully functional.

   gcloudeventarctriggerslist--location=${REGION}

   The output should be similar to the following:

   NAME: helloworld-events
   TYPE: google.cloud.pubsub.topic.v1.messagePublished
   DESTINATION: Cloud Run service: helloworld-events
   ACTIVE: Yes
   LOCATION: us-central1
   

Trigger the function

To test the Pub/Sub function:

1. Assign the topic to a variable:

   TOPIC_ID=$(gcloud eventarc triggers describe TRIGGER_NAME --location $REGION --format='value(transport.pubsub.topic)')
   

2. Publish a message to the topic:

   gcloud pubsub topics publish $TOPIC_ID --message="Hello World"
   

The Cloud Run service logs the body of the incoming message. You can view this in the Logs section of your Cloud Run instance:

1. Navigate to the Google Cloud console.
2. Click the function.

3. Select the Logs tab.

   Logs might take a few moments to appear. If you don't see them immediately, check again after a few moments.

4. Look for the "Hello World!" message.