Sessions with WCF Service

Sessions in WCF refers controlling correlation of messages between two end points.

Session Modes

• Allowed: Clients can connect with or without establishing session 
• Required: Client can connect only with establishing session 
• NotAllowed: Client can connect only without session

    [ServiceContract(SessionMode= SessionMode.Required)]

    public interface IService1

    {

        [OperationContract]

        string GetData();

    }

Session is not supported by all bindings. Only WS-*, netTcpBinding & netNamedPipe are support wcf sessions.

If we use bindings other than mentioned above, service throws exception

Instance Context Modes

• PerCall: Each request made to the service is served by a new instance of service
• PerSession: All requests made to the service served by a single service instance for a particular single session
• Single: All request made to the service served by a single service instance even from different clients

   [ServiceBehavior(InstanceContextMode= InstanceContextMode.PerSession)]

    public class Service1 : IService1

    {

       int counter = 0;

        public string GetData()

        {

            return string.Format("Counter : {0} , Session Id: {1}", counter++, OperationContext.Current.SessionId);

        }

    }

Below are the results of 9 scenarios

Session Mode : Allowed

1. InstanceContextMode.PerCall : Session maintained but new instance serving every method call

2. InstanceContextMode.PerSession : Session maintained with every client and only one instance serving all calls for a particular session with a client

3. InstanceContextMode.Single : Session maintained with every client only one service instance serving all service calls from all clients doesn't matter session

Session Mode : NotAllowed
1. InstanceContextMode.PerCall : Session not maintained every call served by new instance

2. InstanceContextMode.PerSession : Session not maintained every call served by new instance

3. InstanceContextMode.Single : Session not maintained every call to the service is served by single instance of service to all clients

Session Mode :Required

1. InstanceContextMode.PerCall : Session maintained every call served by new instance

2. InstanceContextMode.PerSession : Session maintained with every client & calls to the service served by one instance within established particular sessions between clients and service

3. InstanceContextMode.Single : Session maintained between clients and service & only one instance serving all calls to the service from all the clients.

Important Links:
http://devproconnections.com/net-framework/load-balancing-and-scaling-your-wcf-services