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Quickstart: Publish and Subscribe

Get started with Dapr’s Publish and Subscribe building block

Let’s take a look at Dapr’s Publish and Subscribe (Pub/sub) building block. In this Quickstart, you will run a publisher microservice and a subscriber microservice to demonstrate how Dapr enables a Pub/sub pattern.

  1. Using a publisher service, developers can repeatedly publish messages to a topic.
  2. A Pub/sub component queues or brokers those messages. Our example below uses Redis, you can use RabbitMQ, Kafka, etc.
  3. The subscriber to that topic pulls messages from the queue and processes them.

Select your preferred language-specific Dapr SDK before proceeding with the Quickstart.


Step 1: Pre-requisites

For this example, you will need:

Step 2: Set up the environment

Clone the sample provided in the Quickstarts repo.

git clone https://github.com/dapr/quickstarts.git

Step 3: Subscribe to topics

In a terminal window, from the root of the Quickstarts clone directory navigate to the order-processor directory.

cd pub_sub/python/sdk/order-processor

Install the dependencies:

pip3 install -r requirements.txt

Run the order-processor subscriber service alongside a Dapr sidecar.

dapr run --app-id order-processor --components-path ../../../components/ --app-port 5001 -- python3 app.py

In the order-processor subscriber, we’re subscribing to the Redis instance called order_pub_sub (as defined in the pubsub.yaml component) and topic orders. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

# Register Dapr pub/sub subscriptions
@app.route('/dapr/subscribe', methods=['GET'])
def subscribe():
    subscriptions = [{
        'pubsubname': 'order_pub_sub',
        'topic': 'orders',
        'route': 'orders'
    }]
    print('Dapr pub/sub is subscribed to: ' + json.dumps(subscriptions))
    return jsonify(subscriptions)


# Dapr subscription in /dapr/subscribe sets up this route
@app.route('/orders', methods=['POST'])
def orders_subscriber():
    event = from_http(request.headers, request.get_data())
    print('Subscriber received : ' + event.data['orderid'], flush=True)
    return json.dumps({'success': True}), 200, {
        'ContentType': 'application/json'}


app.run(port=5001)

Step 4: Publish a topic

In a new terminal window, navigate to the checkout directory.

cd pub_sub/python/sdk/checkout

Install the dependencies:

pip3 install -r requirements.txt

Run the checkout publisher service alongside a Dapr sidecar.

dapr run --app-id checkout --components-path ../../../components/ -- python3 app.py

In the checkout publisher, we’re publishing the orderId message to the Redis instance called order_pub_sub (as defined in the pubsub.yaml component) and topic orders. As soon as the service starts, it publishes in a loop:

with DaprClient() as client:
    # Publish an event/message using Dapr PubSub
    result = client.publish_event(
        pubsub_name='order_pub_sub',
        topic_name='orders',
        data=json.dumps(order),
        data_content_type='application/json',
    )

Step 5: View the Pub/sub outputs

Notice, as specified in the code above, the publisher pushes a random number to the Dapr sidecar while the subscriber receives it.

Publisher output:

== APP == INFO:root:Published data: {"orderId": 1}
== APP == INFO:root:Published data: {"orderId": 2}
== APP == INFO:root:Published data: {"orderId": 3}
== APP == INFO:root:Published data: {"orderId": 4}
== APP == INFO:root:Published data: {"orderId": 5}
== APP == INFO:root:Published data: {"orderId": 6}
== APP == INFO:root:Published data: {"orderId": 7}
== APP == INFO:root:Published data: {"orderId": 8}
== APP == INFO:root:Published data: {"orderId": 9}
== APP == INFO:root:Published data: {"orderId": 10}

Subscriber output:

== APP == INFO:root:Subscriber received: {"orderId": 1}
== APP == INFO:root:Subscriber received: {"orderId": 2}
== APP == INFO:root:Subscriber received: {"orderId": 3}
== APP == INFO:root:Subscriber received: {"orderId": 4}
== APP == INFO:root:Subscriber received: {"orderId": 5}
== APP == INFO:root:Subscriber received: {"orderId": 6}
== APP == INFO:root:Subscriber received: {"orderId": 7}
== APP == INFO:root:Subscriber received: {"orderId": 8}
== APP == INFO:root:Subscriber received: {"orderId": 9}
== APP == INFO:root:Subscriber received: {"orderId": 10}

pubsub.yaml component file

When you run dapr init, Dapr creates a default Redis pubsub.yaml and runs a Redis container on your local machine, located:

  • On Windows, under %UserProfile%\.dapr\components\pubsub.yaml
  • On Linux/MacOS, under ~/.dapr/components/pubsub.yaml

With the pubsub.yaml component, you can easily swap out underlying components without application code changes.

The Redis pubsub.yaml file included for this Quickstart contains the following:

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: order_pub_sub
spec:
  type: pubsub.redis
  version: v1
  metadata:
  - name: redisHost
    value: localhost:6379
  - name: redisPassword
    value: ""

In the YAML file:

  • metadata/name is how your application talks to the component.
  • spec/metadata defines the connection to the instance of the component.
  • scopes specify which application can use the component.

Step 1: Pre-requisites

For this example, you will need:

Step 2: Set up the environment

Clone the sample provided in the Quickstarts repo.

git clone https://github.com/dapr/quickstarts.git

Step 3: Subscribe to topics

In a terminal window, from the root of the Quickstarts clone directory navigate to the order-processor directory.

cd pub_sub/javascript/sdk/order-processor

Install dependencies, which will include the dapr-client package from the JavaScript SDK:

npm install

Verify you have the following files included in the service directory:

  • package.json
  • package-lock.json

Run the order-processor subscriber service alongside a Dapr sidecar.

dapr run --app-port 5001 --app-id order-processing --app-protocol http --dapr-http-port 3501 --components-path ../../../components -- npm run start

In the order-processor subscriber, we’re subscribing to the Redis instance called order_pub_sub (as defined in the pubsub.yaml component) and topic orders. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

server.pubsub.subscribe("order_pub_sub", "orders", (data) => console.log("Subscriber received: " + JSON.stringify(data)));

Step 4: Publish a topic

In a new terminal window, from the root of the Quickstarts clone directory, navigate to the checkout directory.

cd pub_sub/javascript/sdk/checkout

Install dependencies, which will include the dapr-client package from the JavaScript SDK:

npm install

Verify you have the following files included in the service directory:

  • package.json
  • package-lock.json

Run the checkout publisher service alongside a Dapr sidecar.

dapr run --app-id checkout --app-protocol http --dapr-http-port 3500 --components-path ../../../components -- npm run start

In the checkout publisher service, we’re publishing the orderId message to the Redis instance called order_pub_sub (as defined in the pubsub.yaml component) and topic orders. As soon as the service starts, it publishes in a loop:

const client = new DaprClient(DAPR_HOST, DAPR_HTTP_PORT);

await client.pubsub.publish(PUBSUB_NAME, PUBSUB_TOPIC, order);
   console.log("Published data: " + JSON.stringify(order));

Step 5: View the Pub/sub outputs

Notice, as specified in the code above, the publisher pushes a random number to the Dapr sidecar while the subscriber receives it.

Publisher output:

== APP == Published data: {"orderId":1}
== APP == Published data: {"orderId":2}
== APP == Published data: {"orderId":3}
== APP == Published data: {"orderId":4}
== APP == Published data: {"orderId":5}
== APP == Published data: {"orderId":6}
== APP == Published data: {"orderId":7}
== APP == Published data: {"orderId":8}
== APP == Published data: {"orderId":9}
== APP == Published data: {"orderId":10}

Subscriber output:

== APP == Subscriber received: {"orderId":1}
== APP == Subscriber received: {"orderId":2}
== APP == Subscriber received: {"orderId":3}
== APP == Subscriber received: {"orderId":4}
== APP == Subscriber received: {"orderId":5}
== APP == Subscriber received: {"orderId":6}
== APP == Subscriber received: {"orderId":7}
== APP == Subscriber received: {"orderId":8}
== APP == Subscriber received: {"orderId":9}
== APP == Subscriber received: {"orderId":10}

pubsub.yaml component file

When you run dapr init, Dapr creates a default Redis pubsub.yaml and runs a Redis container on your local machine, located:

  • On Windows, under %UserProfile%\.dapr\components\pubsub.yaml
  • On Linux/MacOS, under ~/.dapr/components/pubsub.yaml

With the pubsub.yaml component, you can easily swap out underlying components without application code changes.

The Redis pubsub.yaml file included for this Quickstart contains the following:

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: order_pub_sub
spec:
  type: pubsub.redis
  version: v1
  metadata:
  - name: redisHost
    value: localhost:6379
  - name: redisPassword
    value: ""

In the YAML file:

  • metadata/name is how your application talks to the component.
  • spec/metadata defines the connection to the instance of the component.
  • scopes specify which application can use the component.

Step 1: Pre-requisites

For this example, you will need:

Step 2: Set up the environment

Clone the sample provided in the Quickstarts repo.

git clone https://github.com/dapr/quickstarts.git

Step 3: Subscribe to topics

In a terminal window, from the root of the Quickstarts clone directory navigate to the order-processor directory.

cd pub_sub/csharp/sdk/order-processor

Recall NuGet packages:

dotnet restore
dotnet build

Run the order-processor subscriber service alongside a Dapr sidecar.

dapr run --app-id order-processor --components-path ../../../components --app-port 7001 -- dotnet run

In the order-processor subscriber, we’re subscribing to the Redis instance called order_pub_sub (as defined in the pubsub.yaml component) and topic orders. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

// Dapr subscription in [Topic] routes orders topic to this route
app.MapPost("/orders", [Topic("order_pub_sub", "orders")] (Order order) => {
    Console.WriteLine("Subscriber received : " + order);
    return Results.Ok(order);
});

public record Order([property: JsonPropertyName("orderId")] int OrderId);

Step 4: Publish a topic

In a new terminal window, from the root of the Quickstarts clone directory, navigate to the checkout directory.

cd pub_sub/csharp/sdk/checkout

Recall NuGet packages:

dotnet restore
dotnet build

Run the checkout publisher service alongside a Dapr sidecar.

dapr run --app-id checkout --components-path ../../../components -- dotnet run

In the checkout publisher, we’re publishing the orderId message to the Redis instance called order_pub_sub (as defined in the pubsub.yaml component) and topic orders. As soon as the service starts, it publishes in a loop:

using var client = new DaprClientBuilder().Build();
await client.PublishEventAsync("order_pub_sub", "orders", order);
Console.WriteLine("Published data: " + order);

Step 5: View the Pub/sub outputs

Notice, as specified in the code above, the publisher pushes a random number to the Dapr sidecar while the subscriber receives it.

Publisher output:

== APP == Published data: Order { OrderId = 1 }
== APP == Published data: Order { OrderId = 2 }
== APP == Published data: Order { OrderId = 3 }
== APP == Published data: Order { OrderId = 4 }
== APP == Published data: Order { OrderId = 5 }
== APP == Published data: Order { OrderId = 6 }
== APP == Published data: Order { OrderId = 7 }
== APP == Published data: Order { OrderId = 8 }
== APP == Published data: Order { OrderId = 9 }
== APP == Published data: Order { OrderId = 10 }

Subscriber output:

== APP == Subscriber received: Order { OrderId = 1 }
== APP == Subscriber received: Order { OrderId = 2 }
== APP == Subscriber received: Order { OrderId = 3 }
== APP == Subscriber received: Order { OrderId = 4 }
== APP == Subscriber received: Order { OrderId = 5 }
== APP == Subscriber received: Order { OrderId = 6 }
== APP == Subscriber received: Order { OrderId = 7 }
== APP == Subscriber received: Order { OrderId = 8 }
== APP == Subscriber received: Order { OrderId = 9 }
== APP == Subscriber received: Order { OrderId = 10 }

pubsub.yaml component file

When you run dapr init, Dapr creates a default Redis pubsub.yaml and runs a Redis container on your local machine, located:

  • On Windows, under %UserProfile%\.dapr\components\pubsub.yaml
  • On Linux/MacOS, under ~/.dapr/components/pubsub.yaml

With the pubsub.yaml component, you can easily swap out underlying components without application code changes.

The Redis pubsub.yaml file included for this Quickstart contains the following:

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: order_pub_sub
spec:
  type: pubsub.redis
  version: v1
  metadata:
  - name: redisHost
    value: localhost:6379
  - name: redisPassword
    value: ""

In the YAML file:

  • metadata/name is how your application talks to the component.
  • spec/metadata defines the connection to the instance of the component.
  • scopes specify which application can use the component.

Step 1: Pre-requisites

For this example, you will need:

Step 2: Set up the environment

Clone the sample provided in the Quickstarts repo.

git clone https://github.com/dapr/quickstarts.git

Step 3: Subscribe to topics

In a terminal window, from the root of the Quickstarts clone directory navigate to the order-processor directory.

cd pub_sub/java/sdk/order-processor

Install the dependencies:

mvn clean install

Run the order-processor subscriber service alongside a Dapr sidecar.

dapr run --app-port 8080 --app-id order-processor --components-path ../../../components -- java -jar target/OrderProcessingService-0.0.1-SNAPSHOT.jar

In the order-processor subscriber, we’re subscribing to the Redis instance called order_pub_sub (as defined in the pubsub.yaml component) and topic orders. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

@Topic(name = "orders", pubsubName = "order_pub_sub")
@PostMapping(path = "/orders", consumes = MediaType.ALL_VALUE)
public Mono<ResponseEntity> getCheckout(@RequestBody(required = false) CloudEvent<Order> cloudEvent) {
    return Mono.fromSupplier(() -> {
        try {
            logger.info("Subscriber received: " + cloudEvent.getData().getOrderId());
            return ResponseEntity.ok("SUCCESS");
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    });
}

Step 4: Publish a topic

In a new terminal window, from the root of the Quickstarts clone directory, navigate to the checkout directory.

cd pub_sub/java/sdk/checkout

Install the dependencies:

mvn clean install

Run the checkout publisher service alongside a Dapr sidecar.

dapr run --app-id checkout --components-path ../../../components -- java -jar target/CheckoutService-0.0.1-SNAPSHOT.jar

In the checkout publisher, we’re publishing the orderId message to the Redis instance called order_pub_sub (as defined in the pubsub.yaml component) and topic orders. As soon as the service starts, it publishes in a loop:

DaprClient client = new DaprClientBuilder().build();
client.publishEvent(
		PUBSUB_NAME,
		TOPIC_NAME,
		order).block();
logger.info("Published data: " + order.getOrderId());

Step 5: View the Pub/sub outputs

Notice, as specified in the code above, the publisher pushes a random number to the Dapr sidecar while the subscriber receives it.

Publisher output:

== APP == 7194 [main] INFO com.service.CheckoutServiceApplication - Published data: 1
== APP == 12213 [main] INFO com.service.CheckoutServiceApplication - Published data: 2
== APP == 17233 [main] INFO com.service.CheckoutServiceApplication - Published data: 3
== APP == 22252 [main] INFO com.service.CheckoutServiceApplication - Published data: 4
== APP == 27276 [main] INFO com.service.CheckoutServiceApplication - Published data: 5
== APP == 32320 [main] INFO com.service.CheckoutServiceApplication - Published data: 6
== APP == 37340 [main] INFO com.service.CheckoutServiceApplication - Published data: 7
== APP == 42356 [main] INFO com.service.CheckoutServiceApplication - Published data: 8
== APP == 47386 [main] INFO com.service.CheckoutServiceApplication - Published data: 9
== APP == 52410 [main] INFO com.service.CheckoutServiceApplication - Published data: 10

Subscriber output:

== APP == 2022-03-07 13:31:19.551  INFO 43512 --- [nio-8080-exec-5] c.s.c.OrderProcessingServiceController   : Subscriber received: 1
== APP == 2022-03-07 13:31:19.552  INFO 43512 --- [nio-8080-exec-9] c.s.c.OrderProcessingServiceController   : Subscriber received: 2
== APP == 2022-03-07 13:31:19.551  INFO 43512 --- [nio-8080-exec-6] c.s.c.OrderProcessingServiceController   : Subscriber received: 3
== APP == 2022-03-07 13:31:19.552  INFO 43512 --- [nio-8080-exec-2] c.s.c.OrderProcessingServiceController   : Subscriber received: 4
== APP == 2022-03-07 13:31:19.553  INFO 43512 --- [nio-8080-exec-2] c.s.c.OrderProcessingServiceController   : Subscriber received: 5
== APP == 2022-03-07 13:31:19.553  INFO 43512 --- [nio-8080-exec-9] c.s.c.OrderProcessingServiceController   : Subscriber received: 6
== APP == 2022-03-07 13:31:22.849  INFO 43512 --- [nio-8080-exec-3] c.s.c.OrderProcessingServiceController   : Subscriber received: 7
== APP == 2022-03-07 13:31:27.866  INFO 43512 --- [nio-8080-exec-6] c.s.c.OrderProcessingServiceController   : Subscriber received: 8
== APP == 2022-03-07 13:31:32.895  INFO 43512 --- [nio-8080-exec-6] c.s.c.OrderProcessingServiceController   : Subscriber received: 9
== APP == 2022-03-07 13:31:37.919  INFO 43512 --- [nio-8080-exec-2] c.s.c.OrderProcessingServiceController   : Subscriber received: 10

pubsub.yaml component file

When you run dapr init, Dapr creates a default Redis pubsub.yaml and runs a Redis container on your local machine, located:

  • On Windows, under %UserProfile%\.dapr\components\pubsub.yaml
  • On Linux/MacOS, under ~/.dapr/components/pubsub.yaml

With the pubsub.yaml component, you can easily swap out underlying components without application code changes.

The Redis pubsub.yaml file included for this Quickstart contains the following:

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: order_pub_sub
spec:
  type: pubsub.redis
  version: v1
  metadata:
  - name: redisHost
    value: localhost:6379
  - name: redisPassword
    value: ""
scopes:
  - orderprocessing
  - checkout

In the YAML file:

  • metadata/name is how your application talks to the component.
  • spec/metadata defines the connection to the instance of the component.
  • scopes specify which application can use the component.

Step 1: Pre-requisites

For this example, you will need:

Step 2: Set up the environment

Clone the sample provided in the Quickstarts repo.

git clone https://github.com/dapr/quickstarts.git

Step 3: Subscribe to topics

In a terminal window, from the root of the Quickstarts clone directory navigate to the order-processor directory.

cd pub_sub/go/sdk/order-processor

Install the dependencies and build the application:

go build app.go

Run the order-processor subscriber service alongside a Dapr sidecar.

dapr run --app-port 6001 --app-id order-processor --app-protocol http --dapr-http-port 3501 --components-path ../../../components -- go run app.go

In the order-processor subscriber, we’re subscribing to the Redis instance called order_pub_sub (as defined in the pubsub.yaml component) and topic orders. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

func eventHandler(ctx context.Context, e *common.TopicEvent) (retry bool, err error) {
	fmt.Println("Subscriber received: ", e.Data)
	return false, nil
}

Step 4: Publish a topic

In a new terminal window, from the root of the Quickstarts clone directory, navigate to the checkout directory.

cd pub_sub/go/sdk/checkout

Install the dependencies and build the application:

go build app.go

Run the checkout publisher service alongside a Dapr sidecar.

dapr run --app-id checkout --app-protocol http --dapr-http-port 3500 --components-path ../../../components -- go run app.go

In the checkout publisher, we’re publishing the orderId message to the Redis instance called order_pub_sub (as defined in the pubsub.yaml component) and topic orders. As soon as the service starts, it publishes in a loop:

client, err := dapr.NewClient()

if err := client.PublishEvent(ctx, PUBSUB_NAME, PUBSUB_TOPIC, []byte(order)); err != nil {
    panic(err)
}

fmt.Sprintf("Published data: ", order)

Step 5: View the Pub/sub outputs

Notice, as specified in the code above, the publisher pushes a numbered message to the Dapr sidecar while the subscriber receives it.

Publisher output:

== APP == dapr client initializing for: 127.0.0.1:63293
== APP == Published data:  {"orderId":1}
== APP == Published data:  {"orderId":2}
== APP == Published data:  {"orderId":3}
== APP == Published data:  {"orderId":4}
== APP == Published data:  {"orderId":5}
== APP == Published data:  {"orderId":6}
== APP == Published data:  {"orderId":7}
== APP == Published data:  {"orderId":8}
== APP == Published data:  {"orderId":9}
== APP == Published data:  {"orderId":10}

Subscriber output:

== APP == Subscriber received:  {"orderId":1}
== APP == Subscriber received:  {"orderId":2}
== APP == Subscriber received:  {"orderId":3}
== APP == Subscriber received:  {"orderId":4}
== APP == Subscriber received:  {"orderId":5}
== APP == Subscriber received:  {"orderId":6}
== APP == Subscriber received:  {"orderId":7}
== APP == Subscriber received:  {"orderId":8}
== APP == Subscriber received:  {"orderId":9}
== APP == Subscriber received:  {"orderId":10}

Note: the order in which they are received may vary.

pubsub.yaml component file

When you run dapr init, Dapr creates a default Redis pubsub.yaml and runs a Redis container on your local machine, located:

  • On Windows, under %UserProfile%\.dapr\components\pubsub.yaml
  • On Linux/MacOS, under ~/.dapr/components/pubsub.yaml

With the pubsub.yaml component, you can easily swap out underlying components without application code changes.

The Redis pubsub.yaml file included for this Quickstart contains the following:

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: order_pub_sub
spec:
  type: pubsub.redis
  version: v1
  metadata:
  - name: redisHost
    value: localhost:6379
  - name: redisPassword
    value: ""
scopes:
  - orderprocessing
  - checkout

In the YAML file:

  • metadata/name is how your application talks to the component.
  • spec/metadata defines the connection to the instance of the component.
  • scopes specify which application can use the component.

Tell us what you think!

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Next steps

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Last modified July 26, 2022: Update translations for v1.6 (#2665) (e18b8c6)