Using Dapr for pub/sub with Azure Service Bus

Table of contents

Step 1: Create Azure Service Bus
Step 2: Configure the pub/sub component
Step 3: Test the application

Stop Simulation, TrafficControlService and FineCollectionService, and VehicleRegistrationService by pressing Crtl-C in the respective terminal windows.

Step 1: Create Azure Service Bus

In this assignment, you will use Azure Service Bus as the message broker with the Dapr pub/sub building block. You’re going to create an Azure Service Bus namespace and a topic in it. To be able to do this, you need to have an Azure subscription. If you don’t have one, you can create a free account at https://azure.microsoft.com/free/.

Login to Azure:
```
 az login
```
Create a resource group:
```
 az group create --name rg-dapr-workshop-java --location eastus
```
A resource group is a container that holds related resources for an Azure solution. The resource group can include all the resources for the solution, or only those resources that you want to manage as a group. In our workshop, all the databases, all the microservices, etc. will be grouped into a single resource group.

Azure Service Bus Namespace is a logical container for topics, queues, and subscriptions. This namespace needs to be globally unique. Use the following command to generate a unique name:

Linux/Unix shell:

  UNIQUE_IDENTIFIER=$(LC_ALL=C tr -dc a-z0-9 </dev/urandom | head -c 5)
  SERVICE_BUS="sb-dapr-workshop-java-$UNIQUE_IDENTIFIER"
  echo $SERVICE_BUS

Powershell:

  $ACCEPTED_CHAR = [Char[]]'abcdefghijklmnopqrstuvwxyz0123456789'
  $UNIQUE_IDENTIFIER = (Get-Random -Count 5 -InputObject $ACCEPTED_CHAR) -join ''
  $SERVICE_BUS = "sb-dapr-workshop-java-$UNIQUE_IDENTIFIER"
  $SERVICE_BUS

Create a Service Bus messaging namespace:

 az servicebus namespace create --resource-group rg-dapr-workshop-java --name $SERVICE_BUS --location eastus

Create a Service Bus topic:

 az servicebus topic create --resource-group rg-dapr-workshop-java --namespace-name $SERVICE_BUS --name test

Create authorization rules for the Service Bus topic:

 az servicebus topic authorization-rule create --resource-group rg-dapr-workshop-java --namespace-name $SERVICE_BUS --topic-name test --name DaprWorkshopJavaAuthRule --rights Manage Send Listen

Get the connection string for the Service Bus topic and copy it to the clipboard:

 az servicebus topic authorization-rule keys list --resource-group rg-dapr-workshop-java --namespace-name $SERVICE_BUS --topic-name test --name DaprWorkshopJavaAuthRule  --query primaryConnectionString --output tsv

Step 2: Configure the pub/sub component

Open the file dapr/azure-servicebus-pubsub.yaml in your code editor.
```
 apiVersion: dapr.io/v1alpha1
 kind: Component
 metadata:
   name: pubsub
 spec:
   type: pubsub.azure.servicebus
   version: v1
   metadata:
   - name: connectionString # Required when not using Azure Authentication.
     value: "Endpoint=sb://{ServiceBusNamespace}.servicebus.windows.net/;SharedAccessKeyName={PolicyName};SharedAccessKey={Key};EntityPath={ServiceBus}"
 scopes:
   - trafficcontrolservice
   - finecollectionservice
```
As you can see, you specify a different type of pub/sub component (pubsub.azure.servicebus) and you specify in the metadata section how to connect to Azure Service Bus created in step 1. For this workshop, you are going to use the connection string you copied in the previous step. You can also configure the component to use Azure Active Directory authentication. For more information, see Azure Service Bus pub/sub component.

In the scopes section, you specify that only the TrafficControlService and FineCollectionService should use the pub/sub building block. To know more about scopes, see Application access to components with scopes.
Copy or Move this file dapr/azure-servicebus-pubsub.yaml to dapr/components folder.
Replace the connectionString value with the value you copied from the clipboard.
Move the files dapr/components/kafka-pubsub.yaml and dap/components/rabbit-pubsub.yaml back to dapr/ folder if they are present in the component folder.

Step 3: Test the application

You’re going to start all the services now.

Make sure no services from previous tests are running (close the command-shell windows).
Open the terminal window and make sure the current folder is VehicleRegistrationService.
Enter the following command to run the VehicleRegistrationService with a Dapr sidecar:
```
mvn spring-boot:run
```
Open a terminal window and change the current folder to FineCollectionService.

Enter the following command to run the FineCollectionService with a Dapr sidecar:

dapr run --app-id finecollectionservice --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 --resources-path ../dapr/components mvn spring-boot:run

Open a terminal window and change the current folder to TrafficControlService.

Enter the following command to run the TrafficControlService with a Dapr sidecar:

dapr run --app-id trafficcontrolservice --app-port 6000 --dapr-http-port 3600 --dapr-grpc-port 60000 --resources-path ../dapr/components mvn spring-boot:run

Open a terminal window and change the current folder to Simulation.
Start the simulation:
```
mvn spring-boot:run
```

You should see the same logs as before. Obviously, the behavior of the application is exactly the same as before. But now, instead of messages being published and subscribed via kafka topic, are being processed through Azure Service Bus.

< Assignment 2 - Run with Dapr Assignment 4 - Observability >