Multiple instances of a self hosted WCF service

Question

We have a "worker" service running from console application in c#, for development we were always running a single instance of this service, which fetches chunks of data and performs some calculations, these chunks of data are provided by another service (which keeps track of how much data is left etc.)

Now in QA we want to run multiple instances of the "worker" service simultaneously (on the same machine).However we are get an exception as soon as the second instance is launched:

The TransportManager failed to listen on the supplied URI using the NetTcpPortSharing service: the URI is already registered with the service.

We are using netTcpBinding and the endpoint address is hardcoded into the app.config and remains the same and because of that I assume we are getting this error.

<services>
    <service behaviorConfiguration="CoreBehavior" name="WorkerService">
        <endpoint address="net.tcp://localhost:8001/WorkerAssignment" binding="netTcpBinding" contract="IWorkerService" bindingConfiguration="CoreTcpBinding"/>
    </service>
</services>
<bindings>
    <netTcpBinding>
        <binding name="CoreTcpBinding" portSharingEnabled="true">
            <security mode="None"/>
        </binding>
    </netTcpBinding>
</bindings> 

Application code :

var host = new ServiceHost(typeof(WorkerService));
host.Open();

How do we provide a different URI for each instance so that atleast the port will remain the same ?

OR If there is a different way to run multiple instances of the same service?

Answer 1

If you want to have multiple instances of the service than it is enough to have single service host - just decorate you WorkerService with ServiceBehaviorAttribute

[ServiceBehavior(InstanceContextMode = InstanceContextMode.Percall)] 
public class WorkerService : IWorkerService 
{
  //...service data
}

This will make sure that every call to the service will first create new instance of the service. Other ways of creating service class can be found here

If, however you would like to have multiple service hosts than it is impossible to have two service hosts that will host same service on completely the same url.

Another case would be if you want to have one service host hosting the same service on multiple endpoints with the same base address and custom uri's. In this case you can make use of overloaded ServiceHost constructor or investigate methods AddBaseAddress , AddServiceEndpoint . Or if you want to do it from configuration file than here's simple example with your code slightly modified

<service behaviorConfiguration="CoreBehavior" name="WorkerService">
    <endpoint address="WorkerAssignment" binding="netTcpBinding" contract="IWorkerService"/>
    <endpoint address="QAWorkerAssignment" binding="netTcpBinding" contract="IWorkerService"/>
  <host>
    <baseAddresses>
      <add baseAddress="net.tcp://localhost:8001/" />
    </baseAddresses>
  </host>
</service>

with this configuration you will have two endpoints for your service

net.tcp://localhost:8001/WorkerAssignment

net.tcp://localhost:8001/QAWorkerAssignment

Answer 2

Murtaza you are right that you still need multiple instances and the issue is how to give different port

Alternate 1: For each instance of service: before calling ServiceHost.Open you can add endpoint to the service

ServiceHost serviceHost = new ServiceHost(typeof(CalculatorService))
WSHttpBinding binding = new WSHttpBinding();
serviceHost.AddServiceEndpoint(typeof(ICalculator), binding, "http://localhost:8000/servicemodelsamples/service/basic");

In above code the address part can have different port for each instance of the service.

For details following link

Alternate 2: Enable port sharing

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.serviceModel>
    <bindings>
      <netTcpBinding>
        <binding portSharingEnabled="true">
          <security mode="None" />
        </binding>
      </netTcpBinding>
    </bindings>
  </system.serviceModel>
</configuration>

Answer 3

You can define your specific behavior

[ServiceBehavior(InstanceContextMode=InstanceContextMode.PerCall, 
                 ConcurrencyMode = ConcurrencyMode.Multiple)]