Pub/Sub without CloudEvents

Use Pub/Sub without CloudEvents.

Introduction

Dapr uses CloudEvents to provide additional context to the event payload, enabling features like:

  • Tracing
  • Deduplication by message Id
  • Content-type for proper deserialization of event’s data

For more information about CloudEvents, read the CloudEvents specification.

When adding Dapr to your application, some services may still need to communicate via raw pub/sub messages not encapsulated in CloudEvents. This may be for compatibility reasons, or because some apps are not using Dapr. Dapr enables apps to publish and subscribe to raw events that are not wrapped in a CloudEvent.

Publishing raw messages

Dapr apps are able to publish raw events to pub/sub topics without CloudEvent encapsulation, for compatibility with non-Dapr apps.

Diagram showing how to publish with Dapr when subscriber does not use Dapr or CloudEvent

To disable CloudEvent wrapping, set the rawPayload metadata to true as part of the publishing request. This allows subscribers to receive these messages without having to parse the CloudEvent schema.


curl -X "POST" http://localhost:3500/v1.0/publish/pubsub/TOPIC_A?metadata.rawPayload=true -H "Content-Type: application/json" -d '{"order-number": "345"}'

from dapr.clients import DaprClient

with DaprClient() as d:
    req_data = {
        'order-number': '345'
    }
    # Create a typed message with content type and body
    resp = d.publish_event(
        pubsub_name='pubsub',
        topic='TOPIC_A',
        data=json.dumps(req_data),
        metadata=(
                     ('rawPayload', 'true')
                 )
    )
    # Print the request
    print(req_data, flush=True)

<?php

require_once __DIR__.'/vendor/autoload.php';

$app = \Dapr\App::create();
$app->run(function(\DI\FactoryInterface $factory) {
    $publisher = $factory->make(\Dapr\PubSub\Publish::class, ['pubsub' => 'pubsub']);
    $publisher->topic('TOPIC_A')->publish('data', ['rawPayload' => 'true']);
});

Subscribing to raw messages

Dapr apps are also able to subscribe to raw events coming from existing pub/sub topics that do not use CloudEvent encapsulation.

Diagram showing how to subscribe with Dapr when publisher does not use Dapr or CloudEvent

Programmatically subscribe to raw events

When subscribing programmatically, add the additional metadata entry for rawPayload so the Dapr sidecar automatically wraps the payloads into a CloudEvent that is compatible with current Dapr SDKs.


import flask
from flask import request, jsonify
from flask_cors import CORS
import json
import sys

app = flask.Flask(__name__)
CORS(app)

@app.route('/dapr/subscribe', methods=['GET'])
def subscribe():
    subscriptions = [{'pubsubname': 'pubsub',
                      'topic': 'deathStarStatus',
                      'route': 'dsstatus',
                      'metadata': {
                          'rawPayload': 'true',
                      } }]
    return jsonify(subscriptions)

@app.route('/dsstatus', methods=['POST'])
def ds_subscriber():
    print(request.json, flush=True)
    return json.dumps({'success':True}), 200, {'ContentType':'application/json'}

app.run()

<?php

require_once __DIR__.'/vendor/autoload.php';

$app = \Dapr\App::create(configure: fn(\DI\ContainerBuilder $builder) => $builder->addDefinitions(['dapr.subscriptions' => [
    new \Dapr\PubSub\Subscription(pubsubname: 'pubsub', topic: 'deathStarStatus', route: '/dsstatus', metadata: [ 'rawPayload' => 'true'] ),
]]));

$app->post('/dsstatus', function(
    #[\Dapr\Attributes\FromBody]
    \Dapr\PubSub\CloudEvent $cloudEvent,
    \Psr\Log\LoggerInterface $logger
    ) {
        $logger->alert('Received event: {event}', ['event' => $cloudEvent]);
        return ['status' => 'SUCCESS'];
    }
);

$app->start();

Declaratively subscribe to raw events

Similarly, you can subscribe to raw events declaratively by adding the rawPayload metadata entry to your Subscription Custom Resource Definition (CRD):

apiVersion: dapr.io/v1alpha1
kind: Subscription
metadata:
  name: myevent-subscription
spec:
  topic: deathStarStatus
  route: /dsstatus
  pubsubname: pubsub
  metadata:
    rawPayload: "true"
scopes:
- app1
- app2