Forums

On the page (jump to):

How to Use Service Bus Queues

This guide will show you how to use Service Bus queues. The samples are written in C# and use the .NET API. The scenarios covered include creating queues, sending and receiving messages, and deleting queues. For more information on queues, see the Next Steps section.

What are Service Bus QueuesWhat are Service Bus Queues

Service Bus Queues support a brokered messaging communication model. When using queues, components of a distributed application do not communicate directly with each other, they instead exchange messages via a queue, which acts as an intermediary. A message producer (sender) hands off a message to the queue and then continues its processing. Asynchronously, a message consumer (receiver) pulls the message from the queue and processes it. The producer does not have to wait for a reply from the consumer in order to continue to process and send further messages. Queues offer First In, First Out (FIFO) message delivery to one or more competing consumers. That is, messages are typically received and processed by the receivers in the order in which they were added to the queue, and each message is received and processed by only one message consumer.

Queue Concepts

Service Bus queues are a general-purpose technology that can be used for a wide variety of scenarios:

Communication between web and worker roles in a multi-tier Windows Azure application
Communication between on-premises apps and Windows Azure hosted apps in a hybrid solution
Communication between components of a distributed application running on-premises in different organizations or departments of an organization

Using queues can enable you to scale out your applications better, and enable more resiliency to your architecture.

Create a Service NamespaceCreate a Service Namespace

To begin using Service Bus queues in Windows Azure, you must first create a service namespace. A service namespace provides a scoping container for addressing Service Bus resources within your application.

To create a service namespace:

Log on to the Windows Azure Management Portal.
In the left navigation pane of the Management Portal, click Service Bus.
In the lower pane of the Management Portal, click Create.
In the Add a new namespace dialog, enter a namespace name. The system immediately checks to see if the name is available.
After making sure the namespace name is available, choose the country or region in which your namespace should be hosted (make sure you use the same country/region in which you are deploying your compute resources).

IMPORTANT: Pick the same region that you intend to choose for deploying your application. This will give you the best performance.
Click the check mark. The system now creates your service namespace and enables it. You might have to wait several minutes as the system provisions resources for your account.

The namespace you created will then appear in the Management Portal and takes a moment to activate. Wait until the status is Active before continuing.

Obtain Management CredentialsObtain the Default Management Credentials for the Namespace

In order to perform management operations, such as creating a queue, on the new namespace, you must obtain the management credentials for the namespace.

In the left navigation pane, click the Service Bus node, to display the list of available namespaces:
Select the namespace you just created from the list shown:
Click Access Key.
In the Connect to your namespace dialog, find the Default Issuer and Default Key entries. Make a note of these values, as you will use this information below to perform operations with the namespace.

Configure the ApplicationConfigure the Application to Use Service Bus

When you create an application that uses Service Bus, you must add a reference to the Service Bus assembly and include the corresponding namespaces.

Add a Reference to the Service Bus Assembly

In Visual Studio's Solution Explorer, right-click References, and then click Add Reference.
In the Browse tab, go to C:\Program Files\Microsoft SDKs\Windows Azure\.NET SDK\v2.0\ref and add a Microsoft.ServiceBus.dll reference.

Import the Service Bus Namespaces

Add the following to the top of any C# file where you want to use Service Bus queues:

using Microsoft.ServiceBus;
using Microsoft.ServiceBus.Messaging;

You are now ready to write code against the Service Bus.

Set Up the Connection StringHow to Set Up a Service Bus Connection String

The Service Bus uses a connection string to store endpoints and credentials. You can put your connection string in a configuration file, rather than hard-coding it in code:

When using Windows Azure Cloud Services, it is recommended you store your connection string using the Windows Azure service configuration system (*.csdef and *.cscfg files).
When using Windows Azure Web Sites or Windows Azure Virtual Machines, it is recommended you store your connection string using the .NET configuration system (e.g. web.config file).

In both cases, you can retrieve your connection string using the CloudConfigurationManager.GetSetting method as shown later in this guide.

Configuring your connection string when using Cloud Services

The service configuration mechanism is unique to Windows Azure Cloud Services projects and enables you to dynamically change configuration settings from the Windows Azure Management Portal without redeploying your application. For example, add a Setting to your service definition (*.csdef) file, as shown below:

<ServiceDefinition name="WindowsAzure1">
...
    <WebRole name="MyRole" vmsize="Small">
        <ConfigurationSettings>
            <Setting name="Microsoft.ServiceBus.ConnectionString" />
        </ConfigurationSettings>
    </WebRole>
...
</ServiceDefinition>

You then specify values in the service configuration (*.cscfg) file:

<ServiceConfiguration serviceName="WindowsAzure1">
...
    <Role name="MyRole">
        <ConfigurationSettings>
            <Setting name="Microsoft.ServiceBus.ConnectionString" 
                     value="Endpoint=sb://[yourServiceNamespace].servicebus.windows.net/;SharedSecretIssuer=[issuerName];SharedSecretValue=[yourDefaultKey]" />
        </ConfigurationSettings>
    </Role>
...
</ServiceConfiguration>

Use the issuer and key values retrieved from the Management Portal as described in the previous section.

Configuring your connection string when using Web Sites or Virtual Machines

When using Web Sites or Virtual Machines, it is recommended you use the .NET configuration system (e.g. web.config). You store the connection string using the <appSettings> element:

<configuration>
    <appSettings>
        <add key="Microsoft.ServiceBus.ConnectionString"
             value="Endpoint=sb://[yourServiceNamespace].servicebus.windows.net/;SharedSecretIssuer=[issuerName];SharedSecretValue=[yourDefaultKey]" />
    </appSettings>
</configuration>

Use the issuer and key values retrieved from the Management Portal as described in the previous section.

How to Create a QueueHow to Create a Queue

You can perform management operations for Service Bus queues via the NamespaceManager class. The NamespaceManager class provides methods to create, enumerate, and delete queues.

This example constructs a NamespaceManager object using the Windows Azure CloudConfigurationManager class with a connection string consisting of the base address of a Service Bus service namespace and the appropriate credentials with permissions to manage it. This connection string is of the form

Endpoint=sb://[yourServiceNamespace].servicebus.windows.net/;SharedSecretIssuer=[issuerName];SharedSecretValue=[yourDefaultKey]

For example, given the configuration settings in the previous section:

// Create the queue if it does not exist already
string connectionString = 
    CloudConfigurationManager.GetSetting("Microsoft.ServiceBus.ConnectionString");

var namespaceManager = 
    NamespaceManager.CreateFromConnectionString(connectionString);

if (!namespaceManager.QueueExists("TestQueue"))
{
    namespaceManager.CreateQueue("TestQueue");
}

There are overloads of the CreateQueue method that enable you to tune properties of the queue (for example, to set the default "time-to-live" value to be applied to messages sent to the queue). These settings are applied by using the QueueDescription class. The following example shows how to create a queue named "TestQueue" with a maximum size of 5GB and a default message time-to-live of 1 minute:

// Configure Queue Settings
QueueDescription qd = new QueueDescription("TestQueue");
qd.MaxSizeInMegabytes = 5120;
qd.DefaultMessageTimeToLive = new TimeSpan(0, 1, 0);

// Create a new Queue with custom settings
string connectionString = 
    CloudConfigurationManager.GetSetting("Microsoft.ServiceBus.ConnectionString");

var namespaceManager = 
    NamespaceManager.CreateFromConnectionString(connectionString);

if (!namespaceManager.QueueExists("TestQueue"))
{
    namespaceManager.CreateQueue(qd);
}

Note: You can use the QueueExists method on NamespaceManager objects to check if a queue with a specified name already exists within a service namespace.

Send Messages to a QueueHow to Send Messages to a Queue

To send a message to a Service Bus queue, your application creates a QueueClient object using the connection string.

The code below demonstrates how to create a QueueClient object for the "TestQueue" queue created above using the CreateFromConnectionString API call:

string connectionString = 
    CloudConfigurationManager.GetSetting("Microsoft.ServiceBus.ConnectionString");

QueueClient Client = 
    QueueClient.CreateFromConnectionString(connectionString, "TestQueue");

Client.Send(new BrokeredMessage());

Messages sent to (and received from) Service Bus queues are instances of the BrokeredMessage class. BrokeredMessage objects have a set of standard properties (such as Label and TimeToLive), a dictionary that is used to hold custom application specific properties, and a body of arbitrary application data. An application can set the body of the message by passing any serializable object into the constructor of the BrokeredMessage, and the appropriate DataContractSerializer will then be used to serialize the object. Alternatively, a System.IO.Stream can be provided.

The following example demonstrates how to send five test messages to the "TestQueue" QueueClient obtained in the code snippet above:

for (int i=0; i<5; i++)
 {
   // Create message, passing a string message for the body
   BrokeredMessage message = new BrokeredMessage("Test message " + i);

   // Set some addtional custom app-specific properties
   message.Properties["TestProperty"] = "TestValue";
   message.Properties["Message number"] = i;   

   // Send message to the queue
   Client.Send(message);
 }

Service Bus queues support a maximum message size of 256 Kb (the header, which includes the standard and custom application properties, can have a maximum size of 64 Kb). There is no limit on the number of messages held in a queue but there is a cap on the total size of the messages held by a queue. This queue size is defined at creation time, with an upper limit of 5 GB.

Receive Messages from a QueueHow to Receive Messages from a Queue

The easiest way to receive messages from a queue is to use a QueueClient object. These objects can work in two different modes: ReceiveAndDelete and PeekLock.

When using the ReceiveAndDelete mode, the receive is a single-shot operation - that is, when the Service Bus receives a read request for a message in a queue, it marks the message as consumed, and returns it to the application. ReceiveAndDelete mode is the simplest model and works best for scenarios in which an application can tolerate not processing a message in the event of a failure. To understand this, consider a scenario in which the consumer issues the receive request and then crashes before processing it. Because the Service Bus will have marked the message as being consumed, when the application restarts and begins consuming messages again, it will have missed the message that was consumed prior to the crash.

In PeekLock mode (which is the default mode), the receive becomes a two-stage operation, which makes it possible to support applications that cannot tolerate missing messages. When the Service Bus receives a request, it finds the next message to be consumed, locks it to prevent other consumers receiving it, and then returns it to the application. After the application finishes processing the message (or stores it reliably for future processing), it completes the second stage of the receive process by calling Complete on the received message. When the Service Bus sees the Complete call, it marks the message as being consumed and removes it from the queue.

The example below demonstrates how messages can be received and processed using the default PeekLock mode. To specify a different ReceiveMode value, you can use another overload for CreateFromConnectionString. This example creates an infinite loop and processes messages as they arrive into the "TestQueue":

Client.Receive();

// Continuously process messages sent to the "TestQueue" 
while (true) 
{  
   BrokeredMessage message = Client.Receive();

   if (message != null)
   {
      try 
      {
         Console.WriteLine("Body: " + message.GetBody<string>());
         Console.WriteLine("MessageID: " + message.MessageId);
         Console.WriteLine("Test Property: " + 
            message.Properties["TestProperty"]);

         // Remove message from queue
         message.Complete();
      }
      catch (Exception)
      {
         // Indicate a problem, unlock message in queue
         message.Abandon();
      }
   }
}

Application Crashes and Unreadable MessagesHow to Handle Application Crashes and Unreadable Messages

The Service Bus provides functionality to help you gracefully recover from errors in your application or difficulties processing a message. If a receiver application is unable to process the message for some reason, then it can call the Abandon method on the received message (instead of the Complete method). This will cause the Service Bus to unlock the message within the queue and make it available to be received again, either by the same consuming application or by another consuming application.

There is also a timeout associated with a message locked within the queue, and if the application fails to process the message before the lock timeout expires (for example, if the application crashes), then the Service Bus unlocks the message automatically and makes it available to be received again.

In the event that the application crashes after processing the message but before the Complete request is issued, then the message will be redelivered to the application when it restarts. This is often called At Least Once Processing, that is, each message will be processed at least once but in certain situations the same message may be redelivered. If the scenario cannot tolerate duplicate processing, then application developers should add additional logic to their application to handle duplicate message delivery. This is often achieved using the MessageId property of the message, which will remain constant across delivery attempts.

Next StepsNext Steps

Now that you've learned the basics of Service Bus queues, follow these links to learn more.

See the MSDN Reference: Queues, Topics, and Subscriptions.
Build a working application that sends and receives messages to and from a Service Bus queue: Service Bus Brokered Messaging .NET Tutorial.