Get started with Azure Service Bus topics and subscriptions (.NET)

This quickstart shows how to send messages to a Service Bus topic and receive messages from a subscription to that topic by using the Azure.Messaging.ServiceBus .NET library.

In this quickstart, you'll do the following steps:

1. Create a Service Bus namespace, using the Azure portal.
2. Create a Service Bus topic, using the Azure portal.
3. Create a Service Bus subscription to that topic, using the Azure portal.
4. Write a .NET console application to send a set of messages to the topic.
5. Write a .NET console application to receive those messages from the subscription.

Prerequisites

If you're new to the service, see Service Bus overview before you do this quickstart.

• Azure subscription. To use Azure services, including Azure Service Bus, you need a subscription. If you don't have an existing Azure account, you can sign up for a trial subscription.
• Visual Studio 2022. The sample application makes use of new features that were introduced in C# 10. You can still use the Service Bus client library with previous C# language versions, but the syntax might vary. To use the latest syntax, we recommend that you install .NET 6.0, or higher and set the language version to latest. If you're using Visual Studio, versions before Visual Studio 2022 aren't compatible with the tools needed to build C# 10 projects.

Create a namespace in the Azure portal

To begin using Service Bus messaging entities in Azure, you must first create a namespace with a name that is unique across Azure. A namespace provides a scoping container for Service Bus resources (queues, topics, etc.) within your application.

To create a namespace:

1. Sign in to the Azure portal.

2. Navigate to the All services page.

3. On the left navigation bar, select Integration from the list of categories, hover the mouse over Service Bus, and then select + button on the Service Bus tile.

   

4. In the Basics tag of the Create namespace page, follow these steps:

   1. For Subscription, choose an Azure subscription in which to create the namespace.

   2. For Resource group, choose an existing resource group in which the namespace will live, or create a new one.

   3. Enter a name for the namespace. The namespace name should adhere to the following naming conventions:

      • The name must be unique across Azure. The system immediately checks to see if the name is available.
      • The name length is at least 6 and at most 50 characters.
      • The name can contain only letters, numbers, hyphens "-".
      • The name must start with a letter and end with a letter or number.
      • The name doesn't end with "-sb" or "-mgmt".

   4. For Location, choose the region in which your namespace should be hosted.

   5. For Pricing tier, select the pricing tier (Basic, Standard, or Premium) for the namespace. For this quickstart, select Standard.

      Important

      If you want to use topics and subscriptions, choose either Standard or Premium. Topics/subscriptions aren't supported in the Basic pricing tier.

      If you selected the Premium pricing tier, specify the number of messaging units. The premium tier provides resource isolation at the CPU and memory level so that each workload runs in isolation. This resource container is called a messaging unit. A premium namespace has at least one messaging unit. You can select 1, 2, 4, 8 or 16 messaging units for each Service Bus Premium namespace. For more information, see Service Bus Premium Messaging.

   6. Select Review + create at the bottom of the page.

      

   7. On the Review + create page, review settings, and select Create.

5. Once the deployment of the resource is successful, select Go to resource on the deployment page.

   

6. You see the home page for your service bus namespace.

   

Create a topic using the Azure portal

1. On the Service Bus Namespace page, select Topics on the left menu.

2. Select + Topic on the toolbar.

3. Enter a name for the topic. Leave the other options with their default values.

4. Select Create.

   

Create a subscription to the topic

1. Select the topic that you created in the previous section.

   

2. On the Service Bus Topic page, select + Subscription on the toolbar.

   

3. On the Create subscription page, follow these steps:

   1. Enter S1 for name of the subscription.

   2. Enter 3 for Max delivery count.

   3. Then, select Create to create the subscription.

      

Authenticate the app to Azure

This quick start shows you two ways of connecting to Azure Service Bus: passwordless and connection string. The first option shows you how to use your security principal in Azure Active Directory and role-based access control (RBAC) to connect to a Service Bus namespace. You don't need to worry about having hard-coded connection string in your code or in a configuration file or in a secure storage like Azure Key Vault. The second option shows you how to use a connection string to connect to a Service Bus namespace. If you are new to Azure, you may find the connection string option easier to follow. We recommend using the passwordless option in real-world applications and production environments. For more information, see Authentication and authorization. You can also read more about passwordless authentication on the overview page.

Launch Visual Studio and sign-in to Azure

You can authorize access to the service bus namespace using the following steps:

1. Launch Visual Studio. If you see the Get started window, select the Continue without code link in the right pane.

2. Select the Sign in button in the top right of Visual Studio.

   

3. Sign-in using the Microsoft Entra account you assigned a role to previously.

   

Send messages to the topic

This section shows you how to create a .NET console application to send messages to a Service Bus topic.

Create a console application

1. In Visual Studio, select File -> New -> Project menu.
2. On the Create a new project dialog box, do the following steps: If you don't see this dialog box, select File on the menu, select New, and then select Project.

   1. Select C# for the programming language.

   2. Select Console for the type of the application.

   3. Select Console App from the results list.

   4. Then, select Next.

      

3. Enter TopicSender for the project name, ServiceBusTopicQuickStart for the solution name, and then select Next.
4. On the Additional information page, select Create to create the solution and the project.

Add the NuGet packages to the project

Add code to send messages to the topic

1. Replace the contents of Program.cs with the following code. The important steps are outlined in this section, with additional information in the code comments.

   • Passwordless
   • Connection String

   1. Creates a ServiceBusClient object using the DefaultAzureCredential object. DefaultAzureCredential automatically discovers and uses the credentials of your Visual Studio sign-in to authenticate to Azure Service Bus.
   2. Invokes the CreateSender method on the ServiceBusClient object to create a ServiceBusSender object for the specific Service Bus topic.
   3. Creates a ServiceBusMessageBatch object by using the ServiceBusSender.CreateMessageBatchAsync.
   4. Add messages to the batch using the ServiceBusMessageBatch.TryAddMessage.
   5. Sends the batch of messages to the Service Bus topic using the ServiceBusSender.SendMessagesAsync method.

   Important

   Update placeholder values (<NAMESPACE-NAME> and <TOPIC-NAME>) in the code snippet with names of your Service Bus namespace and topic.

   using System.Threading.Tasks;
   using Azure.Messaging.ServiceBus;
   using Azure.Identity;
   
   // the client that owns the connection and can be used to create senders and receivers
   ServiceBusClient client;
   
   // the sender used to publish messages to the topic
   ServiceBusSender sender;
   
   // number of messages to be sent to the topic
   const int numOfMessages = 3;
   
   // The Service Bus client types are safe to cache and use as a singleton for the lifetime
   // of the application, which is best practice when messages are being published or read
   // regularly.
   
   //TODO: Replace the "<NAMESPACE-NAME>" and "<TOPIC-NAME>" placeholders.
   client = new ServiceBusClient(
       "<NAMESPACE-NAME>.servicebus.chinacloudapi.cn",
       new DefaultAzureCredential());
   sender = client.CreateSender("<TOPIC-NAME>");
   
   // create a batch 
   using ServiceBusMessageBatch messageBatch = await sender.CreateMessageBatchAsync();
   
   for (int i = 1; i <= numOfMessages; i++)
   {
       // try adding a message to the batch
       if (!messageBatch.TryAddMessage(new ServiceBusMessage($"Message {i}")))
       {
           // if it is too large for the batch
           throw new Exception($"The message {i} is too large to fit in the batch.");
       }
   }
   
   try
   {
       // Use the producer client to send the batch of messages to the Service Bus topic
       await sender.SendMessagesAsync(messageBatch);
       Console.WriteLine($"A batch of {numOfMessages} messages has been published to the topic.");
   }
   finally
   {
       // Calling DisposeAsync on client types is required to ensure that network
       // resources and other unmanaged objects are properly cleaned up.
       await sender.DisposeAsync();
       await client.DisposeAsync();
   }
   
   Console.WriteLine("Press any key to end the application");
   Console.ReadKey();
   

2. Build the project, and ensure that there are no errors.

3. Run the program and wait for the confirmation message.

   A batch of 3 messages has been published to the topic
   

   Important

   In most cases, it will take a minute or two for the role assignment to propagate in Azure. In rare cases, it might take up to eight minutes. If you receive authentication errors when you first run your code, wait a few moments and try again.

4. In the Azure portal, follow these steps:

   1. Navigate to your Service Bus namespace.

   2. On the Overview page, in the bottom-middle pane, switch to the Topics tab, and select the Service Bus topic. In the following example, it's mytopic.

      

   3. On the Service Bus Topic page, In the Messages chart in the bottom Metrics section, you can see that there are three incoming messages for the topic. If you don't see the value, wait for a few minutes, and refresh the page to see the updated chart.

      

   4. Select the subscription in the bottom pane. In the following example, it's S1. On the Service Bus Subscription page, you see the Active message count as 3. The subscription has received the three messages that you sent to the topic, but no receiver has picked them yet.

      

Receive messages from a subscription

In this section, you create a .NET console application that receives messages from the subscription to the Service Bus topic.

Create a project for the receiver

1. In the Solution Explorer window, right-click the ServiceBusTopicQuickStart solution, point to Add, and select New Project.
2. Select Console application, and select Next.
3. Enter SubscriptionReceiver for the Project name, and select Next.
4. On the Additional information page, select Create.
5. In the Solution Explorer window, right-click SubscriptionReceiver, and select Set as a Startup Project.

Add the NuGet packages to the project

Add code to receive messages from the subscription

In this section, you add code to retrieve messages from the subscription.

1. Replace the existing contents of Program.cs with the following properties and methods:

   • Passwordless
   • Connection String

   using System.Threading.Tasks;
   using Azure.Messaging.ServiceBus;
   using Azure.Identity;
   
   // the client that owns the connection and can be used to create senders and receivers
   ServiceBusClient client;
   
   // the processor that reads and processes messages from the subscription
   ServiceBusProcessor processor;    
   
   // handle received messages
   async Task MessageHandler(ProcessMessageEventArgs args)
   {
       string body = args.Message.Body.ToString();
       Console.WriteLine($"Received: {body} from subscription.");
   
       // complete the message. messages is deleted from the subscription. 
       await args.CompleteMessageAsync(args.Message);
   }
   
   // handle any errors when receiving messages
   Task ErrorHandler(ProcessErrorEventArgs args)
   {
       Console.WriteLine(args.Exception.ToString());
       return Task.CompletedTask;
   }
   

2. Append the following code to the end of Program.cs.

   • Passwordless
   • Connection String

   • Creates a ServiceBusClient object using the DefaultAzureCredential object. DefaultAzureCredential automatically discovers and uses the credentials of your Visual Studio sign-in to authenticate to Azure Service Bus.
   • Invokes the CreateProcessor method on the ServiceBusClient object to create a ServiceBusProcessor object for the specified Service Bus topic.
   • Specifies handlers for the ProcessMessageAsync and ProcessErrorAsync events of the ServiceBusProcessor object.
   • Starts processing messages by invoking the StartProcessingAsync on the ServiceBusProcessor object.
   • When user presses a key to end the processing, invokes the StopProcessingAsync on the ServiceBusProcessor object.

   Important

   Update placeholder values (<NAMESPACE-NAME>, <TOPIC-NAME>, <SUBSCRIPTION-NAME>) in the code snippet with names of your Service Bus namespace, topic, and subscription.

   For more information, see code comments.

   // The Service Bus client types are safe to cache and use as a singleton for the lifetime
   // of the application, which is best practice when messages are being published or read
   // regularly.
   //
   // Create the clients that we'll use for sending and processing messages.
   // TODO: Replace the <NAMESPACE-NAME> placeholder
   client = new ServiceBusClient(
       "<NAMESPACE-NAME>.servicebus.chinacloudapi.cn",
       new DefaultAzureCredential());
   
   // create a processor that we can use to process the messages
   // TODO: Replace the <TOPIC-NAME> and <SUBSCRIPTION-NAME> placeholders
   processor = client.CreateProcessor("<TOPIC-NAME>", "<SUBSCRIPTION-NAME>", new ServiceBusProcessorOptions());
   
   try
   {
       // add handler to process messages
       processor.ProcessMessageAsync += MessageHandler;
   
       // add handler to process any errors
       processor.ProcessErrorAsync += ErrorHandler;
   
       // start processing 
       await processor.StartProcessingAsync();
   
       Console.WriteLine("Wait for a minute and then press any key to end the processing");
       Console.ReadKey();
   
       // stop processing 
       Console.WriteLine("\nStopping the receiver...");
       await processor.StopProcessingAsync();
       Console.WriteLine("Stopped receiving messages");
   }
   finally
   {
       // Calling DisposeAsync on client types is required to ensure that network
       // resources and other unmanaged objects are properly cleaned up.
       await processor.DisposeAsync();
       await client.DisposeAsync();
   }
   

3. Here's what your Program.cs should look like:

   • Passwordless
   • Connection String

   using System;
   using System.Threading.Tasks;
   using Azure.Messaging.ServiceBus;
   using Azure.Identity;
   
   // the client that owns the connection and can be used to create senders and receivers
   ServiceBusClient client;
   
   // the processor that reads and processes messages from the subscription
   ServiceBusProcessor processor;
   
   // handle received messages
   async Task MessageHandler(ProcessMessageEventArgs args)
   {
       string body = args.Message.Body.ToString();
       Console.WriteLine($"Received: {body} from subscription.");
   
       // complete the message. messages is deleted from the subscription. 
       await args.CompleteMessageAsync(args.Message);
   }
   
   // handle any errors when receiving messages
   Task ErrorHandler(ProcessErrorEventArgs args)
   {
       Console.WriteLine(args.Exception.ToString());
       return Task.CompletedTask;
   }
   
   // The Service Bus client types are safe to cache and use as a singleton for the lifetime
   // of the application, which is best practice when messages are being published or read
   // regularly.
   //
   // Create the clients that we'll use for sending and processing messages.
   // TODO: Replace the <NAMESPACE-NAME> placeholder
   client = new ServiceBusClient(
       "<NAMESPACE-NAME>.servicebus.chinacloudapi.cn",
       new DefaultAzureCredential());
   
   // create a processor that we can use to process the messages
   // TODO: Replace the <TOPIC-NAME> and <SUBSCRIPTION-NAME> placeholders
   processor = client.CreateProcessor("<TOPIC-NAME>", "<SUBSCRIPTION-NAME>", new ServiceBusProcessorOptions());
   
   try
   {
       // add handler to process messages
       processor.ProcessMessageAsync += MessageHandler;
   
       // add handler to process any errors
       processor.ProcessErrorAsync += ErrorHandler;
   
       // start processing 
       await processor.StartProcessingAsync();
   
       Console.WriteLine("Wait for a minute and then press any key to end the processing");
       Console.ReadKey();
   
       // stop processing 
       Console.WriteLine("\nStopping the receiver...");
       await processor.StopProcessingAsync();
       Console.WriteLine("Stopped receiving messages");
   }
   finally
   {
       // Calling DisposeAsync on client types is required to ensure that network
       // resources and other unmanaged objects are properly cleaned up.
       await processor.DisposeAsync();
       await client.DisposeAsync();
   }
   

4. Build the project, and ensure that there are no errors.

5. Run the receiver application. You should see the received messages. Press any key to stop the receiver and the application.

   Wait for a minute and then press any key to end the processing
   Received: Message 1 from subscription: S1
   Received: Message 2 from subscription: S1
   Received: Message 3 from subscription: S1
   
   Stopping the receiver...
   Stopped receiving messages
   

6. Check the portal again.

   • On the Service Bus Topic page, in the Messages chart, you see three incoming messages and three outgoing messages. If you don't see these numbers, wait for a few minutes, and refresh the page to see the updated chart.

     

   • On the Service Bus Subscription page, you see the Active message count as zero. It's because a receiver has received messages from this subscription and completed the messages.

     

Next steps

See the following documentation and samples:

• Azure Service Bus client library for .NET - Readme
• .NET samples for Azure Service Bus on GitHub
• .NET API reference