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Message reliablity


When a message is sent across the network many things can go wrong. The message can be lost, dropped or sent in wrong order. This can happen due to a variety of reason, network failure, network congestion and proxy failure are few reasons among many other reasons. 

WCF Reliablity features sessions are used to take care most of the above issues. There are two types of reliability Message reliability and Transport reliability. These reliability features simplifies coding needed.

Enabling reliable session

Reliable sessions are built on top of SOAP messaging and enables connection maintenance, verification and message ordering. Turning on reliable session allow the application to ignore duplicates, retry dropped connection and reestablish connections, notify service when the client is not available anymore. However, the cost of this reliability is increased traffic.

Reliable session is easy to turn on. For some binding the reliable session is on by default whereas for other binding its off by default.
  • wsHttpBinding          - default is off
  • netTcpBinding           - default is off
  • wsDualHttpBinding    - default is on
1. Open the WCF service application that you created earlier or download start file here.

2. To make a session reliable, open the App.config of the host and add the following updates to the the binding configuration. 

        <bindings>
          <wsHttpBinding>
            <binding name ="WsHttpBindingConfig">
              <reliableSession />
            </binding>
          </wsHttpBinding>
        </bindings>

 3. To order the messages set the ordered property to true. 
<reliableSession ordered="true" /> 

Enabling Queued Messaging 

Enabling message queues makes the message persist until the message is successfully transferred across the wire. This allows asynchronous communication between the client and the server. This means the services and the client that consume that service do not have to be up and running at the same time making service host and client to be loosely coupled. Such feature is ideal in scenarios where the service may have to serve a huge loads temporarily.

4. To enable queued messages, first we need a queue. To create a queue, MSMQ should be installed. To check, open Computer Management and check if there is Message Queuing under Services and Applications. If not you will have to install MSMQ, do step 5, or else do step 8.

5. Open Control Panel (Win key + X > select Control Panel) > Programs > Programs and Features > Turn Windows features on or off > Expand Microsoft Message Queue (MSMQ) Server Core > check MSMQ HTTP Support >  click OK

6. Open Computer Management, expand Services and Applications, Expand Message Queuing > right click on Private Queues > select New > Private Queue > type productservice > click OK.

7. To use MSMQ with WCF you have to ensure that all the contract is marked OneWay. When using endpoint configured to use MSMQ, it is important to ensure all the operationcontract is marked IsOneWay=true. Update OperationContract of SubmitReview as shown below: 

    [ServiceContract]
    public interface IProductService
    {
        [OperationContract(IsOneWay=true)]
        void SubmitReview (ProductReview pr);

    }

8. Add the endpoint for MSMQ

<endpoint address="net.msmq://localhost/private/productservice" binding="netMsmqBinding"
bindingConfiguration="NetMsmqBindingConfig" contract="ProductServiceLibrary.IProductService" />


9. Add binding configuration for the above endpoint
       <bindings>
        <netMsmqBinding>
          <binding name="NetMsmqBindingConfig" exactlyOnce="false">
            <security mode="None"></security>
          </binding>
        </netMsmqBinding>

        </bindings>

10. Test the console host. It should work without any issues.

11. Update the service reference in the client.

ProductServiceClient client = new ProductServiceClient("NetMsmqBinding_IProductService");

12. Run the Service Host and Client at the same time and test it.

13. Now run only the service client and notice that it accepts a new product review even when the host is not running.

14. Go the Computer Management and check the ProductReview Queue you notice that there is a message that has been queued.

15 Try submitting another product review using the client, now you should see two messages queued

16. Now run the service host. Notice that service host now shows that two reviews have been added.

17. Check the productReview queue in the computer management you will not see any message queued now.

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