---
type: docs
title: "Quickstart: Publish and Subscribe"
linkTitle: "Publish and Subscribe"
weight: 73
description: "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]({{< ref pubsub >}}). 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.
1. [A Pub/sub component](https://docs.dapr.io/concepts/components-concept/#pubsub-brokers) queues or brokers those messages. Our example below uses Redis, you can use RabbitMQ, Kafka, etc.
1. The subscriber to that topic pulls messages from the queue and processes them.

<img src="/images/pubsub-quickstart/pubsub-diagram.png" width=800 style="padding-bottom:15px;">

You can try out this pub/sub quickstart by either:

- [Running all applications in this sample simultaneously with the Multi-App Run template file]({{< ref "#run-using-multi-app-run" >}}), or
- [Running one application at a time]({{< ref "#run-one-application-at-a-time" >}})

## Run using Multi-App Run

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

{{< tabs "Python" "JavaScript" ".NET" "Java" "Go" >}}
 <!-- Python -->
{{% codetab %}}

### Step 1: Pre-requisites

For this example, you will need:

- [Dapr CLI and initialized environment](https://docs.dapr.io/getting-started).
- [Python 3.7+ installed](https://www.python.org/downloads/).
<!-- IGNORE_LINKS -->
- [Docker Desktop](https://www.docker.com/products/docker-desktop)
<!-- END_IGNORE -->

### Step 2: Set up the environment

Clone the [sample provided in the Quickstarts repo](https://github.com/dapr/quickstarts/tree/master/pub_sub).

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

From the root of the Quickstarts directory, navigate into the pub/sub directory:

```bash
cd pub_sub/python/sdk
```

### Step 3: Run the publisher and subscriber

With the following command, simultaneously run the following services alongside their own Dapr sidecars:
- The `order-processor` subscriber
- The `checkout` publisher 

```bash
dapr run -f .
```

**Expected output**

```
== APP - checkout-sdk == Published data: Order { OrderId = 1 }
== APP - order-processor == Subscriber received : Order { OrderId = 1 }
== APP - checkout-sdk == Published data: Order { OrderId = 2 }
== APP - order-processor == Subscriber received : Order { OrderId = 2 }
== APP - checkout-sdk == Published data: Order { OrderId = 3 }
== APP - order-processor == Subscriber received : Order { OrderId = 3 }
== APP - checkout-sdk == Published data: Order { OrderId = 4 }
== APP - order-processor == Subscriber received : Order { OrderId = 4 }
== APP - checkout-sdk == Published data: Order { OrderId = 5 }
== APP - order-processor == Subscriber received : Order { OrderId = 5 }
== APP - checkout-sdk == Published data: Order { OrderId = 6 }
== APP - order-processor == Subscriber received : Order { OrderId = 6 }
== APP - checkout-sdk == Published data: Order { OrderId = 7 }
== APP - order-processor == Subscriber received : Order { OrderId = 7 }
== APP - checkout-sdk == Published data: Order { OrderId = 8 }
== APP - order-processor == Subscriber received : Order { OrderId = 8 }
== APP - checkout-sdk == Published data: Order { OrderId = 9 }
== APP - order-processor == Subscriber received : Order { OrderId = 9 }
== APP - checkout-sdk == Published data: Order { OrderId = 10 }
== APP - order-processor == Subscriber received : Order { OrderId = 10 }
Exited App successfully
```

### What happened?

When you ran `dapr init` during Dapr install, the following YAML files were generated in the `.dapr/components` directory: 
- [`dapr.yaml` Multi-App Run template file]({{< ref "#dapryaml-multi-app-run-template-file" >}})
- [`pubsub.yaml` component file]({{< ref "#pubsubyaml-component-file" >}})

Running `dapr run -f .` in this Quickstart started both the [subscriber]({{< ref "#order-processor-subscriber" >}}) and [publisher]({{< ref "#checkout-publisher" >}}) applications. 

##### `dapr.yaml` Multi-App Run template file

Running the [Multi-App Run template file]({{< ref multi-app-dapr-run >}}) with `dapr run -f .` starts all applications in your project. In this Quickstart, the `dapr.yaml` file contains the following:

```yml
version: 1
common:
  resourcesPath: ../../components/
apps:
  - appID: order-processor-sdk
    appDirPath: ./order-processor/
    appPort: 6001
    command: ["uvicorn", "app:app"]
  - appID: checkout-sdk
    appDirPath: ./checkout/
    command: ["python3", "app.py"]
```

##### `pubsub.yaml` component file

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:

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

In the component 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.

##### `order-processor` subscriber

In the `order-processor` subscriber, you subscribe to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

```py
# Register Dapr pub/sub subscriptions
@app.route('/dapr/subscribe', methods=['GET'])
def subscribe():
    subscriptions = [{
        'pubsubname': 'orderpubsub',
        '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)
```

##### `checkout` publisher

In the `checkout` publisher, you publish the orderId message to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. As soon as the service starts, it publishes in a loop:

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

{{% /codetab %}}

 <!-- JavaScript -->
{{% codetab %}}

### Step 1: Pre-requisites

For this example, you will need:

- [Dapr CLI and initialized environment](https://docs.dapr.io/getting-started).
- [Latest Node.js installed](https://nodejs.org/download/).
<!-- IGNORE_LINKS -->
- [Docker Desktop](https://www.docker.com/products/docker-desktop)
<!-- END_IGNORE -->

### Step 2: Set up the environment

Clone the [sample provided in the Quickstarts repo](https://github.com/dapr/quickstarts/tree/master/pub_sub).

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

From the root of the Quickstarts directory, navigate into the pub/sub directory:

```bash
cd pub_sub/javascript/sdk
```

### Step 3: Run the publisher and subscriber

With the following command, simultaneously run the following services alongside their own Dapr sidecars:
- The `order-processor` subscriber
- The `checkout` publisher 

```bash
dapr run -f .
```

**Expected output**

```
== APP - checkout-sdk == Published data: Order { OrderId = 1 }
== APP - order-processor == Subscriber received : Order { OrderId = 1 }
== APP - checkout-sdk == Published data: Order { OrderId = 2 }
== APP - order-processor == Subscriber received : Order { OrderId = 2 }
== APP - checkout-sdk == Published data: Order { OrderId = 3 }
== APP - order-processor == Subscriber received : Order { OrderId = 3 }
== APP - checkout-sdk == Published data: Order { OrderId = 4 }
== APP - order-processor == Subscriber received : Order { OrderId = 4 }
== APP - checkout-sdk == Published data: Order { OrderId = 5 }
== APP - order-processor == Subscriber received : Order { OrderId = 5 }
== APP - checkout-sdk == Published data: Order { OrderId = 6 }
== APP - order-processor == Subscriber received : Order { OrderId = 6 }
== APP - checkout-sdk == Published data: Order { OrderId = 7 }
== APP - order-processor == Subscriber received : Order { OrderId = 7 }
== APP - checkout-sdk == Published data: Order { OrderId = 8 }
== APP - order-processor == Subscriber received : Order { OrderId = 8 }
== APP - checkout-sdk == Published data: Order { OrderId = 9 }
== APP - order-processor == Subscriber received : Order { OrderId = 9 }
== APP - checkout-sdk == Published data: Order { OrderId = 10 }
== APP - order-processor == Subscriber received : Order { OrderId = 10 }
Exited App successfully
```

### What happened?

When you ran `dapr init` during Dapr install, the following YAML files were generated in the `.dapr/components` directory: 
- [`dapr.yaml` Multi-App Run template file]({{< ref "#dapryaml-multi-app-run-template-file" >}})
- [`pubsub.yaml` component file]({{< ref "#pubsubyaml-component-file" >}})

Running `dapr run -f .` in this Quickstart started both the [subscriber]({{< ref "#order-processor-subscriber" >}}) and [publisher]({{< ref "#checkout-publisher" >}}) applications. 

##### `dapr.yaml` Multi-App Run template file

Running the [Multi-App Run template file]({{< ref multi-app-dapr-run >}}) with `dapr run -f .` starts all applications in your project. In this Quickstart, the `dapr.yaml` file contains the following:

```yml
version: 1
common:
  resourcesPath: ../../components/
apps:
  - appID: order-processor
    appDirPath: ./order-processor/
    appPort: 5002
    command: ["npm", "run", "start"]
  - appID: checkout-sdk
    appDirPath: ./checkout/
    command: ["npm", "run", "start"]
```

##### `pubsub.yaml` component file

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:

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

In the component 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.

##### `order-processor` subscriber

In the `order-processor` subscriber, you subscribe to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

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

##### `checkout` publisher

In the `checkout` publisher service, you publish the orderId message to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. As soon as the service starts, it publishes in a loop:

```js
const client = new DaprClient();

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

{{% /codetab %}}

 <!-- .NET -->
{{% codetab %}}

### Step 1: Pre-requisites

For this example, you will need:

- [Dapr CLI and initialized environment](https://docs.dapr.io/getting-started).
- [.NET SDK or .NET 6 SDK installed](https://dotnet.microsoft.com/download).
<!-- IGNORE_LINKS -->
- [Docker Desktop](https://www.docker.com/products/docker-desktop)
<!-- END_IGNORE -->

### Step 2: Set up the environment

Clone the [sample provided in the Quickstarts repo](https://github.com/dapr/quickstarts/tree/master/pub_sub).

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

From the root of the Quickstarts directory, navigate into the pub/sub directory:

```bash
cd pub_sub/csharp/sdk
```

### Step 3: Run the publisher and subscriber

With the following command, simultaneously run the following services alongside their own Dapr sidecars:
- The `order-processor` subscriber
- The `checkout` publisher 

```bash
dapr run -f .
```

**Expected output**

```
== APP - checkout-sdk == Published data: Order { OrderId = 1 }
== APP - order-processor == Subscriber received : Order { OrderId = 1 }
== APP - checkout-sdk == Published data: Order { OrderId = 2 }
== APP - order-processor == Subscriber received : Order { OrderId = 2 }
== APP - checkout-sdk == Published data: Order { OrderId = 3 }
== APP - order-processor == Subscriber received : Order { OrderId = 3 }
== APP - checkout-sdk == Published data: Order { OrderId = 4 }
== APP - order-processor == Subscriber received : Order { OrderId = 4 }
== APP - checkout-sdk == Published data: Order { OrderId = 5 }
== APP - order-processor == Subscriber received : Order { OrderId = 5 }
== APP - checkout-sdk == Published data: Order { OrderId = 6 }
== APP - order-processor == Subscriber received : Order { OrderId = 6 }
== APP - checkout-sdk == Published data: Order { OrderId = 7 }
== APP - order-processor == Subscriber received : Order { OrderId = 7 }
== APP - checkout-sdk == Published data: Order { OrderId = 8 }
== APP - order-processor == Subscriber received : Order { OrderId = 8 }
== APP - checkout-sdk == Published data: Order { OrderId = 9 }
== APP - order-processor == Subscriber received : Order { OrderId = 9 }
== APP - checkout-sdk == Published data: Order { OrderId = 10 }
== APP - order-processor == Subscriber received : Order { OrderId = 10 }
Exited App successfully
```

### What happened?

When you ran `dapr init` during Dapr install, the following YAML files were generated in the `.dapr/components` directory: 
- [`dapr.yaml` Multi-App Run template file]({{< ref "#dapryaml-multi-app-run-template-file" >}})
- [`pubsub.yaml` component file]({{< ref "#pubsubyaml-component-file" >}})

Running `dapr run -f .` in this Quickstart started both the [subscriber]({{< ref "#order-processor-subscriber" >}}) and [publisher]({{< ref "#checkout-publisher" >}}) applications. 

##### `dapr.yaml` Multi-App Run template file

Running the [Multi-App Run template file]({{< ref multi-app-dapr-run >}}) with `dapr run -f .` starts all applications in your project. In this Quickstart, the `dapr.yaml` file contains the following:

```yml
version: 1
common:
  resourcesPath: ../../components/
apps:
  - appID: order-processor
    appDirPath: ./order-processor/
    appPort: 7006
    command: ["dotnet", "run"]
  - appID: checkout-sdk
    appDirPath: ./checkout/
    command: ["dotnet", "run"]
```

##### `pubsub.yaml` component file

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:

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

In the component 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.

##### `order-processor` subscriber

In the `order-processor` subscriber, you subscribe to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

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

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

##### `checkout` publisher

In the `checkout` publisher, you publish the orderId message to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. As soon as the service starts, it publishes in a loop:

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

{{% /codetab %}}

 <!-- Java -->
{{% codetab %}}

### Step 1: Pre-requisites

For this example, you will need:

- [Dapr CLI and initialized environment](https://docs.dapr.io/getting-started).
- Java JDK 11 (or greater):
  - [Oracle JDK](https://www.oracle.com/java/technologies/downloads), or
  - OpenJDK
- [Apache Maven](https://maven.apache.org/install.html), version 3.x.
<!-- IGNORE_LINKS -->
- [Docker Desktop](https://www.docker.com/products/docker-desktop)
<!-- END_IGNORE -->

### Step 2: Set up the environment

Clone the [sample provided in the Quickstarts repo](https://github.com/dapr/quickstarts/tree/master/pub_sub).

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

From the root of the Quickstarts directory, navigate into the pub/sub directory:

```bash
cd pub_sub/java/sdk
```

### Step 3: Run the publisher and subscriber

With the following command, simultaneously run the following services alongside their own Dapr sidecars:
- The `order-processor` subscriber
- The `checkout` publisher 

```bash
dapr run -f .
```

**Expected output**

```
== APP - checkout-sdk == Published data: Order { OrderId = 1 }
== APP - order-processor == Subscriber received : Order { OrderId = 1 }
== APP - checkout-sdk == Published data: Order { OrderId = 2 }
== APP - order-processor == Subscriber received : Order { OrderId = 2 }
== APP - checkout-sdk == Published data: Order { OrderId = 3 }
== APP - order-processor == Subscriber received : Order { OrderId = 3 }
== APP - checkout-sdk == Published data: Order { OrderId = 4 }
== APP - order-processor == Subscriber received : Order { OrderId = 4 }
== APP - checkout-sdk == Published data: Order { OrderId = 5 }
== APP - order-processor == Subscriber received : Order { OrderId = 5 }
== APP - checkout-sdk == Published data: Order { OrderId = 6 }
== APP - order-processor == Subscriber received : Order { OrderId = 6 }
== APP - checkout-sdk == Published data: Order { OrderId = 7 }
== APP - order-processor == Subscriber received : Order { OrderId = 7 }
== APP - checkout-sdk == Published data: Order { OrderId = 8 }
== APP - order-processor == Subscriber received : Order { OrderId = 8 }
== APP - checkout-sdk == Published data: Order { OrderId = 9 }
== APP - order-processor == Subscriber received : Order { OrderId = 9 }
== APP - checkout-sdk == Published data: Order { OrderId = 10 }
== APP - order-processor == Subscriber received : Order { OrderId = 10 }
Exited App successfully
```

### What happened?

When you ran `dapr init` during Dapr install, the following YAML files were generated in the `.dapr/components` directory: 
- [`dapr.yaml` Multi-App Run template file]({{< ref "#dapryaml-multi-app-run-template-file" >}})
- [`pubsub.yaml` component file]({{< ref "#pubsubyaml-component-file" >}})

Running `dapr run -f .` in this Quickstart started both the [subscriber]({{< ref "#order-processor-subscriber" >}}) and [publisher]({{< ref "#checkout-publisher" >}}) applications. 

##### `dapr.yaml` Multi-App Run template file

Running the [Multi-App Run template file]({{< ref multi-app-dapr-run >}}) with `dapr run -f .` starts all applications in your project. In this Quickstart, the `dapr.yaml` file contains the following:

```yml
version: 1
common:
  resourcesPath: ../../components/
apps:
  - appID: order-processor-sdk
    appDirPath: ./order-processor/target/
    appPort: 8080
    command: ["java", "-jar", "OrderProcessingService-0.0.1-SNAPSHOT.jar"]
  - appID: checkout-sdk
    appDirPath: ./checkout/target/
    command: ["java", "-jar", "CheckoutService-0.0.1-SNAPSHOT.jar"]
```

##### `pubsub.yaml` component file

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:

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

In the component 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.

##### `order-processor` subscriber

In the `order-processor` subscriber, you subscribe to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

```java
@Topic(name = "orders", pubsubName = "orderpubsub")
@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);
        }
    });
}
```

##### `checkout` publisher

In the `checkout` publisher, you publish the orderId message to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. As soon as the service starts, it publishes in a loop:

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

{{% /codetab %}}

 <!-- Go -->
{{% codetab %}}

### Step 1: Pre-requisites

For this example, you will need:

- [Dapr CLI and initialized environment](https://docs.dapr.io/getting-started).
- [Latest version of Go](https://go.dev/dl/).
<!-- IGNORE_LINKS -->
- [Docker Desktop](https://www.docker.com/products/docker-desktop)
<!-- END_IGNORE -->

### Step 2: Set up the environment

Clone the [sample provided in the Quickstarts repo](https://github.com/dapr/quickstarts/tree/master/pub_sub).

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

From the root of the Quickstarts directory, navigate into the pub/sub directory:

```bash
cd pub_sub/go/sdk
```

### Step 3: Run the publisher and subscriber

With the following command, simultaneously run the following services alongside their own Dapr sidecars:
- The `order-processor` subscriber
- The `checkout` publisher 

```bash
dapr run -f .
```

**Expected output**

```
== APP - checkout-sdk == Published data: Order { OrderId = 1 }
== APP - order-processor == Subscriber received : Order { OrderId = 1 }
== APP - checkout-sdk == Published data: Order { OrderId = 2 }
== APP - order-processor == Subscriber received : Order { OrderId = 2 }
== APP - checkout-sdk == Published data: Order { OrderId = 3 }
== APP - order-processor == Subscriber received : Order { OrderId = 3 }
== APP - checkout-sdk == Published data: Order { OrderId = 4 }
== APP - order-processor == Subscriber received : Order { OrderId = 4 }
== APP - checkout-sdk == Published data: Order { OrderId = 5 }
== APP - order-processor == Subscriber received : Order { OrderId = 5 }
== APP - checkout-sdk == Published data: Order { OrderId = 6 }
== APP - order-processor == Subscriber received : Order { OrderId = 6 }
== APP - checkout-sdk == Published data: Order { OrderId = 7 }
== APP - order-processor == Subscriber received : Order { OrderId = 7 }
== APP - checkout-sdk == Published data: Order { OrderId = 8 }
== APP - order-processor == Subscriber received : Order { OrderId = 8 }
== APP - checkout-sdk == Published data: Order { OrderId = 9 }
== APP - order-processor == Subscriber received : Order { OrderId = 9 }
== APP - checkout-sdk == Published data: Order { OrderId = 10 }
== APP - order-processor == Subscriber received : Order { OrderId = 10 }
Exited App successfully
```

### What happened?

When you ran `dapr init` during Dapr install, the following YAML files were generated in the `.dapr/components` directory: 
- [`dapr.yaml` Multi-App Run template file]({{< ref "#dapryaml-multi-app-run-template-file" >}})
- [`pubsub.yaml` component file]({{< ref "#pubsubyaml-component-file" >}})

Running `dapr run -f .` in this Quickstart started both the [subscriber]({{< ref "#order-processor-subscriber" >}}) and [publisher]({{< ref "#checkout-publisher" >}}) applications. 

##### `dapr.yaml` Multi-App Run template file

Running the [Multi-App Run template file]({{< ref multi-app-dapr-run >}}) with `dapr run -f .` starts all applications in your project. In this Quickstart, the `dapr.yaml` file contains the following:

```yml
version: 1
common:
  resourcesPath: ../../components/
apps:
  - appID: order-processor
    appDirPath: ./order-processor/
    appPort: 6005
    command: ["go", "run", "."]
  - appID: checkout-sdk
    appDirPath: ./checkout/
    command: ["go", "run", "."]
```

##### `pubsub.yaml` component file

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:

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

In the component 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.

##### `order-processor` subscriber

In the `order-processor` subscriber, you subscribe to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

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

##### `checkout` publisher

In the `checkout` publisher, you publish the orderId message to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. As soon as the service starts, it publishes in a loop:

```go
client, err := dapr.NewClient()

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

fmt.Println("Published data: ", order)
```

{{% /codetab %}}

{{< /tabs >}}

## Run one application at a time

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

{{< tabs "Python" "JavaScript" ".NET" "Java" "Go" >}}
 <!-- Python -->
{{% codetab %}}

### Step 1: Pre-requisites

For this example, you will need:

- [Dapr CLI and initialized environment](https://docs.dapr.io/getting-started).
- [Python 3.7+ installed](https://www.python.org/downloads/).
<!-- IGNORE_LINKS -->
- [Docker Desktop](https://www.docker.com/products/docker-desktop)
<!-- END_IGNORE -->

### Step 2: Set up the environment

Clone the [sample provided in the Quickstarts repo](https://github.com/dapr/quickstarts/tree/master/pub_sub).

```bash
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.

```bash
cd pub_sub/python/sdk/order-processor
```

Install the dependencies:

```bash
pip3 install -r requirements.txt
```

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

```bash
dapr run --app-id order-processor --resources-path ../../../components/ --app-port 6002 -- python3 app.py
```

> **Note**: Since Python3.exe is not defined in Windows, you may need to use `python app.py` instead of `python3 app.py`.

In the `order-processor` subscriber, we're subscribing to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

```py
# Register Dapr pub/sub subscriptions
@app.route('/dapr/subscribe', methods=['GET'])
def subscribe():
    subscriptions = [{
        'pubsubname': 'orderpubsub',
        '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.

```bash
cd pub_sub/python/sdk/checkout
```

Install the dependencies:

```bash
pip3 install -r requirements.txt
```

Run the `checkout` publisher service alongside a Dapr sidecar.

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

> **Note**: Since Python3.exe is not defined in Windows, you may need to use `python app.py` instead of `python3 app.py`.

In the `checkout` publisher, we're publishing the orderId message to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. As soon as the service starts, it publishes in a loop:

```python
with DaprClient() as client:
    # Publish an event/message using Dapr PubSub
    result = client.publish_event(
        pubsub_name='orderpubsub',
        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:

```yaml
apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: orderpubsub
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.

{{% /codetab %}}

 <!-- JavaScript -->
{{% codetab %}}

### Step 1: Pre-requisites

For this example, you will need:

- [Dapr CLI and initialized environment](https://docs.dapr.io/getting-started).
- [Latest Node.js installed](https://nodejs.org/download/).
<!-- IGNORE_LINKS -->
- [Docker Desktop](https://www.docker.com/products/docker-desktop)
<!-- END_IGNORE -->

### Step 2: Set up the environment

Clone the [sample provided in the Quickstarts repo](https://github.com/dapr/quickstarts/tree/master/pub_sub).

```bash
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.

```bash
cd pub_sub/javascript/sdk/order-processor
```

Install dependencies, which will include the `@dapr/dapr` package from the JavaScript SDK:

```bash
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.

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

In the `order-processor` subscriber, we're subscribing to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

```js
server.pubsub.subscribe("orderpubsub", "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.

```bash
cd pub_sub/javascript/sdk/checkout
```

Install dependencies, which will include the `@dapr/dapr` package from the JavaScript SDK:

```bash
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.

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

In the `checkout` publisher service, we're publishing the orderId message to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. As soon as the service starts, it publishes in a loop:

```js
const client = new DaprClient();

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:

```cli
== 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:

```cli
== 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:

```yaml
apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: orderpubsub
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.

{{% /codetab %}}

 <!-- .NET -->
{{% codetab %}}

### Step 1: Pre-requisites

For this example, you will need:

- [Dapr CLI and initialized environment](https://docs.dapr.io/getting-started).
- [.NET SDK or .NET 6 SDK installed](https://dotnet.microsoft.com/download).
<!-- IGNORE_LINKS -->
- [Docker Desktop](https://www.docker.com/products/docker-desktop)
<!-- END_IGNORE -->

### Step 2: Set up the environment

Clone the [sample provided in the Quickstarts repo](https://github.com/dapr/quickstarts/tree/master/pub_sub).

```bash
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.

```bash
cd pub_sub/csharp/sdk/order-processor
```

Recall NuGet packages:

```bash
dotnet restore
dotnet build
```

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

```bash
dapr run --app-id order-processor --resources-path ../../../components --app-port 7005 -- dotnet run
```

In the `order-processor` subscriber, we're subscribing to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

```cs
// Dapr subscription in [Topic] routes orders topic to this route
app.MapPost("/orders", [Topic("orderpubsub", "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.

```bash
cd pub_sub/csharp/sdk/checkout
```

Recall NuGet packages:

```bash
dotnet restore
dotnet build
```

Run the `checkout` publisher service alongside a Dapr sidecar.

```bash
dapr run --app-id checkout --resources-path ../../../components -- dotnet run
```

In the `checkout` publisher, we're publishing the orderId message to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. As soon as the service starts, it publishes in a loop:

```cs
using var client = new DaprClientBuilder().Build();
await client.PublishEventAsync("orderpubsub", "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:

```dotnetcli
== 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:

```dotnetcli
== 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:

```yaml
apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: orderpubsub
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.

{{% /codetab %}}

 <!-- Java -->
{{% codetab %}}

### Step 1: Pre-requisites

For this example, you will need:

- [Dapr CLI and initialized environment](https://docs.dapr.io/getting-started).
- Java JDK 11 (or greater):
  - [Oracle JDK](https://www.oracle.com/java/technologies/downloads), or
  - OpenJDK
- [Apache Maven](https://maven.apache.org/install.html), version 3.x.
<!-- IGNORE_LINKS -->
- [Docker Desktop](https://www.docker.com/products/docker-desktop)
<!-- END_IGNORE -->

### Step 2: Set up the environment

Clone the [sample provided in the Quickstarts repo](https://github.com/dapr/quickstarts/tree/master/pub_sub).

```bash
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.

```bash
cd pub_sub/java/sdk/order-processor
```

Install the dependencies:

```bash
mvn clean install
```

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

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

In the `order-processor` subscriber, we're subscribing to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

```java
@Topic(name = "orders", pubsubName = "orderpubsub")
@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.

```bash
cd pub_sub/java/sdk/checkout
```

Install the dependencies:

```bash
mvn clean install
```

Run the `checkout` publisher service alongside a Dapr sidecar.

```bash
dapr run --app-id checkout --resources-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 `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. As soon as the service starts, it publishes in a loop:

```java
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:

```yaml
apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: orderpubsub
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.

{{% /codetab %}}

 <!-- Go -->
{{% codetab %}}

### Step 1: Pre-requisites

For this example, you will need:

- [Dapr CLI and initialized environment](https://docs.dapr.io/getting-started).
- [Latest version of Go](https://go.dev/dl/).
<!-- IGNORE_LINKS -->
- [Docker Desktop](https://www.docker.com/products/docker-desktop)
<!-- END_IGNORE -->

### Step 2: Set up the environment

Clone the [sample provided in the Quickstarts repo](https://github.com/dapr/quickstarts/tree/master/pub_sub).

```bash
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.

```bash
cd pub_sub/go/sdk/order-processor
```

Install the dependencies and build the application:

```bash
go build .
```

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

```bash
dapr run --app-port 6002 --app-id order-processor-sdk --app-protocol http --dapr-http-port 3501 --resources-path ../../../components -- go run .
```

In the `order-processor` subscriber, we're subscribing to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. This enables your app code to talk to the Redis component instance through the Dapr sidecar.

```go
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.

```bash
cd pub_sub/go/sdk/checkout
```

Install the dependencies and build the application:

```bash
go build .
```

Run the `checkout` publisher service alongside a Dapr sidecar.

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

In the `checkout` publisher, we're publishing the orderId message to the Redis instance called `orderpubsub` [(as defined in the `pubsub.yaml` component)]({{< ref "#pubsubyaml-component-file" >}}) and topic `orders`. As soon as the service starts, it publishes in a loop:

```go
client, err := dapr.NewClient()

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

fmt.Println("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:

```yaml
apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: orderpubsub
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.

{{% /codetab %}}

{{< /tabs >}}

## Tell us what you think!
We're continuously working to improve our Quickstart examples and value your feedback. Did you find this Quickstart helpful? Do you have suggestions for improvement?

Join the discussion in our [discord channel](https://discord.com/channels/778680217417809931/953427615916638238).

## Next steps

- Set up Pub/sub using HTTP instead of an SDK.
  - [Python](https://github.com/dapr/quickstarts/tree/master/pub_sub/python/http)
  - [JavaScript](https://github.com/dapr/quickstarts/tree/master/pub_sub/javascript/http)
  - [.NET](https://github.com/dapr/quickstarts/tree/master/pub_sub/csharp/http)
  - [Java](https://github.com/dapr/quickstarts/tree/master/pub_sub/java/http)
  - [Go](https://github.com/dapr/quickstarts/tree/master/pub_sub/go/http)
- Learn more about [Pub/sub as a Dapr building block]({{< ref pubsub-overview >}})

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