Yesterday I blogged about content based routing with WCF. Today I want to talk about error handling. What if you route to a service that is not available. WCF allows you to define backup services using a backup list.

So let’s do this: start by building a compatible backup service. In this case I will be using named pipes because this is a very reliable transport:

static Uri ServiceUri = new Uri("net.pipe://localhost/BackupProductService");

static void Main(string[] args)
{
  using (ServiceHost host = new ServiceHost(typeof(BackupProductsService), ServiceUri))
  {
    host.Open();

    Console.ForegroundColor = ConsoleColor.Red;
    Console.WriteLine("Backup product service is running");
    Console.ReadKey();
  }
}

Now let’s create the backup list in the routing service’s configuration:

<routing>

  <backupLists>
    <backupList name="backup">
      <add endpointName="backup" />
    </backupList>  
  </backupLists>
      

This adds a backup endpoint called “backup” which we of course also need to add the the client endpoints:

<client>
  <endpoint address="net.tcp://localhost:8010/ProductService1"
            binding="netTcpBinding" contract="*" name="toys" />
  <endpoint address="net.tcp://localhost:8011/ProductService2"
            binding="netTcpBinding" contract="*" name="beverages" />
  <endpoint address="net.pipe://localhost/BackupProductService"
            binding="netNamedPipeBinding" contract="*" name="backup" />
 </client>

Finally we add the backup list to the filterTable:

<filterTables>
  <filterTable name="productRouting">
     <add filterName="filterToys" endpointName="toys" backupList="backup" />
     <add filterName="noToys" endpointName="beverages" backupList="backup" />
  </filterTable>
</filterTables>

If we now run the sample, but without the toys or beverages service, routing will automatically divert to the backup service.