Using Dead-Letter Queues to Handle Message Transfer Failures
Queued messages can fail delivery. These failed messages are recorded in a dead-letter queue. The failed delivery can be caused by reasons such as network failures, a deleted queue, a full queue, authentication failure, or a failure to deliver on time.
Queued messages can remain in the queue for a long time if the receiving application does not read them from the queue in a timely fashion. This behavior may not be appropriate for time-sensitive messages. Time-sensitive messages have a Time to Live (TTL) property set in the queued binding, which indicates how long the messages can be in the queue before they must expire. Expired messages are sent to a special queue called the dead-letter queue. Messages can also be put in a dead-letter queue for other reasons, such as exceeding a queue quota or because of authentication failure.
Generally, applications write compensation logic to read messages from the dead-letter queue and failure reasons. The compensation logic depends on the cause of the failure. For example, in the case of authentication failure, you can correct the certificate attached with the message and resend the message. If delivery failed because the target queue quota was reached, you can reattempt delivery in the hope that the quota problem was resolved.
Most queuing systems have a system-wide dead-letter queue where all failed messages from that system are stored. Message Queuing (MSMQ) provides two system-wide dead-letter queues: a transactional system-wide dead-letter queue that stores messages that failed delivery to the transactional queue and a non-transactional system-wide dead-letter queue that stores messages that failed delivery to the non-transactional queue. If two clients are sending messages to two different services, and therefore different queues in WCF are sharing the same MSMQ service to send, then it is possible to have a mix of messages in the system dead-letter queue. This is not always optimal. In several cases (security, for example), you may not want one client to read another client's messages from a dead-letter queue. A shared dead-letter queue also requires clients to browse through the queue to find a message that they sent, which can be prohibitively expensive based on the number of messages in the dead-letter queue. Therefore, in WCF NetMsmqBinding, MsmqIntegrationBinding, and MSMQ on Windows Vista provide a custom dead-letter queue (sometimes referred to as an application-specific dead-letter queue).
The custom dead-letter queue provides isolation between clients that share the same MSMQ service to send messages.
On Windows Server 2003 and Windows XP, Windows Communication Foundation (WCF) provides a system-wide dead-letter queue for all queued client applications. On Windows Vista, WCF provides a dead-letter queue for each queued client application.
Specifying Use of the Dead-Letter Queue
A dead-letter queue is in the queue manager of the sending application. It stores messages that have expired or that have failed transfer or delivery.
The binding has the following dead-letter queue properties:
Reading Messages from the Dead-Letter Queue
An application that reads messages out of a dead-letter queue is similar to a WCF service that reads from an application queue, except for the following minor differences:
To read messages from a system transactional dead-letter queue, the Uniform Resource Identifier (URI) must be of the form: net.msmq://localhost/system$;DeadXact.
To read messages from a system non-transactional dead-letter queue, the URI must be of the form: net.msmq://localhost/system$;DeadLetter.
To read messages from a custom dead-letter queue, the URI must be of the form:net.msmq://localhost/private/<custom-dlq-name> where custom-dlq-name is the name of the custom dead-letter queue.
For more information about how to address queues, see Service Endpoints and Queue Addressing.
The WCF stack on the receiver matches addresses that the service is listening on with the address on the message. If the addresses match, the message is dispatched; if not, the message is not dispatched. This can cause problems when reading from the dead-letter queue, because messages in the dead-letter queue are typically addressed to the service and not the dead-letter queue service. Therefore, the service reading from the dead-letter queue must install an address filter ServiceBehavior that instructs the stack to match all messages in the queue independently of the addressee. Specifically, you must add a ServiceBehavior with the Any parameter to the service reading messages from the dead-letter queue.
Poison Message Handling from the Dead-Letter Queue
Poison message handling is available on dead-letter queues, with some conditions. Because you cannot create sub-queues from system queues, when reading from the system dead-letter queue, the ReceiveErrorHandling cannot be set to Move. Note that if you are reading from a custom dead-letter queue, you can have sub-queues and, therefore, Move is a valid disposition for the poison message.
When ReceiveErrorHandling is set to Reject, when reading from the custom dead letter queue, the poison message is put in the system dead-letter queue. If reading from the system dead-letter queue, the message is dropped (purged). A reject from a system dead-letter queue in MSMQ drops (purges) the message.
Example
The following example shows how to create a dead-letter queue and how to use it to process expired messages. The example is based on the example in How to: Exchange Queued Messages with WCF Endpoints. The following example shows how to write the client code to the order processing service that uses a dead-letter queue for each application. The example also shows how to process messages from the dead-letter queue.
The following is code for a client that specifies a dead-letter queue for each application.
using System;
using System.ServiceModel.Channels;
using System.Configuration;
//using System.Messaging;
using System.ServiceModel;
using System.Transactions;
namespace Microsoft.ServiceModel.Samples
{
//The service contract is defined in generatedProxy.cs, generated from the service by the svcutil tool.
//Client implementation code.
class Client
{
static void Main()
{
// Get MSMQ queue name from appsettings in configuration.
string deadLetterQueueName = ConfigurationManager.AppSettings["deadLetterQueueName"];
// Create the transacted MSMQ queue for storing dead message if necessary.
if (!System.Messaging.MessageQueue.Exists(deadLetterQueueName))
System.Messaging.MessageQueue.Create(deadLetterQueueName, true);
OrderProcessorClient client = new OrderProcessorClient("OrderProcessorEndpoint");
try
{
// Create the purchase order.
PurchaseOrder po = new PurchaseOrder();
po.CustomerId = "somecustomer.com";
po.PONumber = Guid.NewGuid().ToString();
PurchaseOrderLineItem lineItem1 = new PurchaseOrderLineItem();
lineItem1.ProductId = "Blue Widget";
lineItem1.Quantity = 54;
lineItem1.UnitCost = 29.99F;
PurchaseOrderLineItem lineItem2 = new PurchaseOrderLineItem();
lineItem2.ProductId = "Red Widget";
lineItem2.Quantity = 890;
lineItem2.UnitCost = 45.89F;
po.orderLineItems = new PurchaseOrderLineItem[2];
po.orderLineItems[0] = lineItem1;
po.orderLineItems[1] = lineItem2;
//Create a transaction scope.
using (TransactionScope scope = new TransactionScope(TransactionScopeOption.Required))
{
// Make a queued call to submit the purchase order.
client.SubmitPurchaseOrder(po);
// Complete the transaction.
scope.Complete();
}
client.Close();
}
catch(TimeoutException timeout)
{
Console.WriteLine(timeout.Message);
client.Abort();
}
catch(CommunicationException conexcp)
{
Console.WriteLine(conexcp.Message);
client.Abort();
}
Console.WriteLine();
Console.WriteLine("Press <ENTER> to terminate client.");
Console.ReadLine();
}
}
}
The following is code for the client configuration file.
<configuration>
<!-- Change "localhost" in the endpoint address to the machine name where the queue resides
Change "localhost" in the customDeadLetterQueue attribute in the binding element to the
machine name where the client application executes
-->
<appSettings>
<!-- use appSetting to configure MSMQ Dead Letter queue name -->
<add key="deadLetterQueueName" value=".\private$\ServiceModelSamplesOrdersAppDLQ"/>
</appSettings>
<system.serviceModel>
<client>
<!-- Define NetMsmqEndpoint -->
<endpoint name="OrderProcessorEndpoint"
address="net.msmq://localhost/private/ServiceModelSamplesDeadLetter"
binding="netMsmqBinding"
bindingConfiguration="PerAppDLQBinding"
contract="IOrderProcessor" />
</client>
<bindings>
<netMsmqBinding>
<binding name="PerAppDLQBinding"
deadLetterQueue="Custom"
customDeadLetterQueue="net.msmq://localhost/private/ServiceModelSamplesOrdersAppDLQ"
timeToLive="00:00:02"/>
</netMsmqBinding>
</bindings>
</system.serviceModel>
</configuration>
The following is code for a service processing messages from a dead-letter queue.
using System;
using System.ServiceModel.Description;
using System.Configuration;
using System.Messaging;
using System.ServiceModel;
using System.ServiceModel.Channels;
using System.Transactions;
namespace Microsoft.ServiceModel.Samples
{
// Define a service contract.
[ServiceContract(Namespace = "http://Microsoft.ServiceModel.Samples")]
public interface IOrderProcessor
{
[OperationContract(IsOneWay = true)]
void SubmitPurchaseOrder(PurchaseOrder po);
}
// Service class that implements the service contract.
// Added code to write output to the console window
[ServiceBehavior(InstanceContextMode = InstanceContextMode.Single, ConcurrencyMode = ConcurrencyMode.Single, AddressFilterMode = AddressFilterMode.Any)]
public class PurchaseOrderDLQService : IOrderProcessor
{
OrderProcessorClient orderProcessorService;
public PurchaseOrderDLQService()
{
orderProcessorService = new OrderProcessorClient("OrderProcessorEndpoint");
}
[OperationBehavior(TransactionScopeRequired = true, TransactionAutoComplete = true)]
public void SimpleSubmitPurchaseOrder(PurchaseOrder po)
{
Console.WriteLine("Submitting purchase order did not succeed ", po);
MsmqMessageProperty mqProp = OperationContext.Current.IncomingMessageProperties[MsmqMessageProperty.Name] as MsmqMessageProperty;
Console.WriteLine("Message Delivery Status: {0} ", mqProp.DeliveryStatus);
Console.WriteLine("Message Delivery Failure: {0}", mqProp.DeliveryFailure);
Console.WriteLine();
}
[OperationBehavior(TransactionScopeRequired = true, TransactionAutoComplete = true)]
public void SubmitPurchaseOrder(PurchaseOrder po)
{
Console.WriteLine("Submitting purchase order did not succeed ", po);
MsmqMessageProperty mqProp = OperationContext.Current.IncomingMessageProperties[MsmqMessageProperty.Name] as MsmqMessageProperty;
Console.WriteLine("Message Delivery Status: {0} ", mqProp.DeliveryStatus);
Console.WriteLine("Message Delivery Failure: {0}", mqProp.DeliveryFailure);
Console.WriteLine();
// Resend the message if timed out.
if (mqProp.DeliveryFailure == DeliveryFailure.ReachQueueTimeout ||
mqProp.DeliveryFailure == DeliveryFailure.ReceiveTimeout)
{
// Re-send.
Console.WriteLine("Purchase order Time To Live expired");
Console.WriteLine("Trying to resend the message");
// Reuse the same transaction used to read the message from dlq to enqueue the message to the application queue.
orderProcessorService.SubmitPurchaseOrder(po);
Console.WriteLine("Purchase order resent");
}
}
// Host the service within this EXE console application.
public static void Main()
{
// Create a ServiceHost for the PurchaseOrderDLQService type.
using (ServiceHost serviceHost = new ServiceHost(typeof(PurchaseOrderDLQService)))
{
// Open the ServiceHostBase to create listeners and start listening for messages.
serviceHost.Open();
// The service can now be accessed.
Console.WriteLine("The dead letter service is ready.");
Console.WriteLine("Press <ENTER> to terminate service.");
Console.WriteLine();
Console.ReadLine();
// Close the ServiceHostBase to shutdown the service.
serviceHost.Close();
}
}
}
}
The following is code for the dead-letter queue service configuration file.
<!-- Change the endpoint address to reflect your machine name.
Place this code in the app.config for the Dead Letter Queue service -->
<configuration>
<system.serviceModel>
<services>
<service
name="Microsoft.ServiceModel.Samples.PurchaseOrderDLQService">
<!-- Define NetMsmqEndpoint in this case, DLQ end point to read messages-->
<endpoint address="net.msmq://localhost/private/ServiceModelSamplesOrdersAppDLQ"
binding="netMsmqBinding"
bindingConfiguration="DefaultBinding"
contract="Microsoft.ServiceModel.Samples.IOrderProcessor" />
</service>
</services>
<client>
<!-- Define NetMsmqEndpoint -->
<endpoint name="OrderProcessorEndpoint"
address="net.msmq://localhost/private/ServiceModelSamplesDeadLetter"
binding="netMsmqBinding"
bindingConfiguration="SystemDLQBinding"
contract="IOrderProcessor" />
</client>
<bindings>
<netMsmqBinding>
<binding name="DefaultBinding" />
<binding name="SystemDLQBinding"
deadLetterQueue="System"/>
</netMsmqBinding>
</bindings>
</system.serviceModel>
</configuration>
See Also
Tasks
How to: Exchange Queued Messages with WCF Endpoints