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.
Table of Contents
What 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.
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 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:
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Log on to the Windows Azure Management Portal.
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In the lower left navigation pane of the Management Portal, click Service Bus, Access Control & Caching.
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In the upper left pane of the Management Portal, click the Service Bus node, and then click the New button.
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In the Create a new Service Namespace dialog, enter a Namespace, and then to make sure that it is unique, click the Check Availability button.
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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), and then click the Create Namespace button.
The namespace you created will then appear in the Management Portal and takes a moment to activate. Wait until the status is Active before moving on.
Obtain the Default Management Credentials for the Namespace
In order to perform management operations, such as creating a queue, on the new namespace, you need to obtain the management credentials for the namespace.
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In the left navigation pane, click the Service Bus node, to display the list of available namespaces:
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Select the namespace you just created from the list shown:
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The right-hand Properties pane will list the properties for the new namespace:
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The Default Key is hidden. Click the View button to display the security credentials:
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Make a note of the Default Issuer and the Default Key as you will use this information below to perform operations with the namespace.
Configure Your Application to Use Service Bus
When you create an application that uses Service Bus, you will need to add a reference to the Service Bus assembly and include the corresponding namespaces.
Add a Reference to the Service Bus Assembly
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In Visual Studio's Solution Explorer, right-click References, and then click Add Reference.
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In the Browse tab, go to C:\Program Files\Windows Azure SDK\v1.6\ServiceBus\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 Service Bus.
How to Create a Security Token Provider
Service Bus uses a claims-based security model implemented using the Windows Azure Access Control Service (ACS). The TokenProvider class provides a security token provider with built-in factory methods. The code below creates a SharedSecretTokenProvider to hold the shared secret credentials and handle the acquisition of the appropriate tokens from the Access Control Service:
string issuer = "<obtained from portal>";
string key = "<obtained from portal>";
TokenProvider tP = TokenProvider.CreateSharedSecretTokenProvider(issuer, key);
Use the issuer and key values retrieved from the Management Portal as described in the previous section.
How to Create a Queue
Management operations for Service Bus queues can be performed via the NamespaceManager class. A NamespaceManager object is constructed with the base address of a Service Bus namespace and an appropriate token provider that has permissions to manage it. The base address of a Service Bus namespace is a URI of the form "sb://.servicebus.windows.net". The ServiceBusEnvironment class provides the CreateServiceUri helper method to assist the creation of these URIs.
The NamespaceManager class provides methods to create, enumerate, and delete queues. The example below shows how a NamespaceManager can be used to create a queue named "TestQueue" within a "HowToSample" service namespace:
string issuer = "<obtained from portal>";
string key = "<obtained from portal>";
TokenProvider tP = TokenProvider.CreateSharedSecretTokenProvider(issuer, key);
// Retrieve URI of our "HowToSample" service namespace (created via the portal)
Uri uri = ServiceBusEnvironment.CreateServiceUri("sb", "HowToSample", string.Empty);
// Create NamespaceManager for our "HowToSample" service namespace
NamespaceManager namespaceManager = new NamespaceManager(uri, tP);
// Create a new Queue named "TestQueue"
namespaceManager.CreateQueue("TestQueue");
There are overloads of the CreateQueue method that allow properties of the queue to be tuned ( 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:
string issuer = "<obtained from portal>";
string key = "<obtained from portal>";
TokenProvider tP = TokenProvider.CreateSharedSecretTokenProvider(issuer, key);
// Retrieve URI of our "HowToSample" service namespace (created via the portal)
Uri uri = ServiceBusEnvironment.CreateServiceUri("sb", "HowToSample", string.Empty);
// Create NamespaceManager for our "HowToSample" service namespace
NamespaceManager namespaceManager = new NamespaceManager(uri, tP);
// 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
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.
How to Send Messages to a Queue
To send a message to a Service Bus Queue, your application will obtain a MessageSender object. Like NamespaceManager objects, this object is created from the base URI of the service namespace and the appropriate token provider.
The below code demonstrates how to retrieve a MessageSender object for the "TestQueue" queue we created above within our "HowToSample" service namespace:
string issuer = "<obtained from portal>";
string key = "<obtained from portal>";
// URI address and token for our "HowToSample" namespace
TokenProvider tP = TokenProvider.CreateSharedSecretTokenProvider(issuer, key);
Uri uri = ServiceBusEnvironment.CreateServiceUri("sb", "HowToSample", string.Empty);
// Retrieve MessageSender for the "TestQueue" within our "HowToSample" namespace
MessagingFactory factory = MessagingFactory.Create(uri, tP);
MessageSender testQueue = factory.CreateMessageSender("TestQueue");
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" MessageSender we 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 additional custom app-specific properties
message.Properties["TestProperty"] = "TestValue";
message.Properties["Message number"] = i;
// Send message to the queue
testQueue.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.
How to Receive Messages from a Queue
The simplest way to receive messages from a queue is to use a MessageReceiver object. MessageReceiver objects can work in two different modes: ReceiveAndDelete and PeekLock.
When using the ReceiveAndDelete mode, receive is a single-shot operation - that is, when Service Bus receives a read request for a message in a queue, it marks the message as being 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 Service Bus will have marked the message as being consumed, then 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), receive becomes a two stage operation, which makes it possible to support applications that cannot tolerate missing messages. When 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 Service Bus sees the Complete call, it will mark the message as being consumed and remove it from the queue.
The example below demonstrates how messages can be received and processed using PeekLock mode (the default mode). The example below does an infinite loop and processes messages as they arrive into our "TestQueue":
string issuer = "<obtained from portal>";
string key = "<obtained from portal>";
// URI address and token for our "HowToSample" namespace
TokenProvider tP = TokenProvider.CreateSharedSecretTokenProvider(issuer, key);
Uri uri = ServiceBusEnvironment.CreateServiceUri("sb", "HowToSample", string.Empty);
// Retrieve MessageReceiver for the "TestQueue" within our "HowToSample" namespace
MessagingFactory factory = MessagingFactory.Create(uri, tP);
MessageReceiver testQueue = factory.CreateMessageReceiver("TestQueue");
// Continuously process messages sent to the "TestQueue"
while (true)
{
BrokeredMessage message = testQueue.Receive();
if (message != null)
{
try
{
Console.WriteLine("Body: " + message.GetBody<string>());
Console.WriteLine("MessageID: " + message.MessageId);
Console.WriteLine("Custom Property: " + message.Properties["TestProperty"]);
// Remove message from queue
message.Complete();
}
catch (Exception)
{
// Indicate a problem, unlock message in queue
message.Abandon();
}
}
}
How to Handle Application Crashes and Unreadable Messages
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 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 (e.g., if the application crashes), then Service Bus will unlock the message automatically and make 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 Steps
Now that you've learned the basics of Service Bus queues, follow these links to learn more.