Azure Service Bus Topics

Introduction

In my last article, I discussed about Azure Service Bus Queue, which is basically a one to one communication. This article tells you how to work with Azure Service Bus topics with a sample console application.

Content

• Service Bus Topics
• Create Service Bus Topics and subscriptions on the Azure portal
• Send and receive a message using service bus topics

Pre-request

• Visual Studio 2017 update 3 or later
• Azure Subscription
• Basic Knowledge of the Azure portal

Azure Service Bus Topics

Topics is similar to Queue but Inside a topic, we have subscriptions and each subscription will have multiple subscribers. The process is simple - just put data to the subscription and one or more subscriber will pull the data out.

Creating a Service Bus Topic in Azure Portal

Step 1

Login into Azure Portal https://portal.azure.com/

Step 2

I’m going to use an existing Azure Service Bus namespace which is used for creating a Queue, please refer to the last article where I have explained how to create an Azure Service Bus and it’ namespace.

Step 3

Once the Azure Service Bus has been created successfully, now, we can start to create a topic for the service bus. Working with topics is similar to queue in Azure Service Bus.

Step 4

Go to Azure service bus namespace. In my case I’m using my existing namespace msgdemobus .

Step 5

In overview, you can find a topic, click on it to add a new topic as shown in the below figure.

 

Step 6 - Add Topic

• Give the name for the topic, in my case I named it as mytopics
• Set a max topic size based on the requirement
• Time for message to live --  by default it will be 14 days
• By enabling duplicate detection, topic will not store any duplicate messages
• By enabling the partioning, the topics itself spreads into multiple storage systems, that means more than one message broker will    be backing up the message.

 

Finally click on create.

Step 7

Once the topic is created successfully, we are able to create a subscription for the topic. In topic overview, click on subscription as shown below.

Step 8

Add the subscription, name the subscription, and I'm going with default values for other fields, as shown below,

 

Send and receive a message using Service Bus Topics

I’m going to create a new console application using C# to send and receive a message with Azure Service Bus Topics using Topic Client.

MyTopicApp.cs

using Microsoft.ServiceBus.Messaging;
using System;


namespace MyTopicApp
{
    class Program
    {
        private static string _serviceBusConn = "Endpoint=sb://<namespace>.servicebus.windows.net/;SharedAccessKeyName=<policy name>;SharedAccessKey=<key>";
        private static string _serviceBustopic = "<Topic Name>";

        static void Main(string[] args)
        {
            SendMessage("Hello I'm Azure Service Bus Topic ");
        }

        static void SendMessage(string message)
        {
            var topicClient = TopicClient.CreateFromConnectionString(_serviceBusConn, _serviceBustopic);
            var msg = new BrokeredMessage(message);
            topicClient.Send(msg);
        }

        static void ReadMessage()
        {
            var subClient = SubscriptionClient.CreateFromConnectionString(_serviceBusConn, _serviceBustopic, "<subscription name>");
            subClient.OnMessage(m =>
            {
                Console.WriteLine(m.GetBody<string>());
            });
        }
    }
}

_serviceBustopic will holds a topic Name.  

_serviceBusConn will hold the Azure service bus connection string, we can get a shared access Name and key from Azure service bus shared access policy as showed in the below figure.

 

 

 Policy Name  

 

Pick a key.

Send Message

SendMessage function is used to send a message to Azure service bus topic using topic client and the BrokeredMessage is used to hold the message.

static void Main(string[] args)
       {
           SendMessage("Hello I'm Azure Service Bus Topic ");
       }

       static void SendMessage(string message)
       {
           var topicClient = TopicClient.CreateFromConnectionString(_conn, _topic);
           var msg = new BrokeredMessage(message);
           topicClient.Send(msg);
       }

Run the program

Switch to Azure portal, you can notice the message count will be updated from 0 to 1. 

 

Read Message

ReadMessage function is used to received a message based on the subscription using subscription client.

static void Main(string[] args)
       {
           ReadMessage();
           Console.ReadKey();
       }
 static void ReadMessage()
       {
           var subClient = SubscriptionClient.CreateFromConnectionString(_serviceBusConn, _serviceBustopic, "MyAppSubscription");
           subClient.OnMessage(m =>
           {
               Console.WriteLine(m.GetBody<string>());

           });
       }

Run a program

Result

 

 

Message is received from topic through subscription.

 

Switch to the Azure portal and you can notice the message count will be updated from 1 to 0. 

 

I hope you have enjoyed this article. Your valuable feedback, questions, or comments about this article are always welcome.