After developing mini project with WCF duplex (Chat Service | Sms Service), I got a Point that maybe not be correct!!
I believed Duplex theory is good and useful but there is a lot problem about using Wcf Duplex. (like reliable session, Time-out exceptions, Client address-Management on server side, proxy management on Client Side)
am I think wrong ? am I miss something?
For more Information I Used wsDualHttpBinding not tcpBinding.
If you need bidirectional communication and you want to use WCF, duplex channels are the way to go. You just need to design your application correctly and correctly handle all problems you have described. If you feel that these problems are overhead and make things even worse you can always use network programming directly (sockets) or handle bidirectional communication by yourselves exposing separate service on server and another on client (where first call from client inform server about clients address) - this scenario will suffer from the same communication problems as WsDualHttpBinding.
WsDualHttpBinding itself is special kind of duplex communication. I personally don't like it because people very often misuse it. The problem is that this binding uses two separate connections - one from client to server and second from server to client. That is big difference to net.tcp where only connection initiated from client to server is used. Obviously using WsDualHttpBinding over internet (= you don't have control over client machines) becomes much more complicated because each client must configure its firewall (in computer, on home internet gateway, etc.) to allow connection on some port. Also if you want to run more then one instance of application on the same client machine, each instance must use its own port.
Related
I am sure that this is answered dozens of times, but I am at a loss as to what keywords to search for and thus I hope that someone can at least tell me where I should be looking given an explanation of my scenario.
I need two services (one can be just a client if that is easier) to talk to each other, but the client will be on a private network whereas the server will be on the internet. I want to be able to push jobs to the client, but the server obviously does not have an IP to hit the client. I'd rather not poll from the client every X seconds. I have read various topics all circling this issue and so I am going to throw out a few terms that I think are relevant, but I am not sure which to use or exactly how.
Comet, SignalR, WebSockets, XSockets, Publisher/Subscriber Pattern...
I have looked at each of these and I am not sure which is the right way to go. The client can certainly "subscribe" to the server on startup, so that should not be an issue. But the client should be either a console app, windows service, or WCF service. It seems Comet and SignalR are more for ASP.NET apps, where the client is JS in a browser. I just need "server(client)" to server connection where the client is behind firewalls.
Which of these terms (or none of them) is a good way to handle server -> client push notifications?
Pub/Sub architecture pattern with something like Azure Service Bus should help you create the solution you desire. This does require that service and the client are aware of the bus. For the plumbing of the client and the services use the WCF which has built in bindings to facilitate the use of this pattern.
Azure: How to Use Service Bus Topics/Subscriptions.
Azure SB has a counter part that works on-premises as well. There are other popular message bus tech (NServiceBus, MasTransit, etc.)
You can have a look at node.js together with socket.io.
This will give everything you need.
socket.io uses web sockets, and if the browser does not support web sockets, it gracefully falls back to other communication mechanism like xhr, flash, polling, aso.
I don't think I was clear. What I meant was How to set a callback("server to client") in a different connection from a "client to server" connection using WCF ?
I always saw callbacks examples using just one DuplexChannelFactory. This implies using only one TCP connection to make client to server calls and receive server to client callbacks.
This question came to me after I read this this topic:
Seeking WCF Duplex "TwoWay" Subscribe+Callback Example
I the top answer, Ian Ringrose said:
Some rules I found to help avoid deadlocks. (Look at my WCF questions to see the pain I had!)
The sever must never call out to a client on the same connection as a call from the same client is in process on.
And/or
The client must never call back to the server on the same connection as is used for the “callbacks” while processing a call-back.
And I was wondering how to implement it using WCF.
This CodeProject on Robust Interapplication Communications using Double-Simplex WCF answers exactly your question:
What I decided to do was run two separate WCF connections (double simplex). Each application would run a WCF Host for incoming messages and each application would run a WCF Client for outgoing messages. This is a pretty robust solution and will not be broken by stopping and starting the applications. The WCF Client simply re-establishes the connection if needed.
The way it is solved meets the requirements you have extracted from the Ian Ringrose answer.
In my application I need to push notifications of real time events from server to clients. The amount of data to pass is very small, mostly and Id. The number of clients listening simultaneously can be around 100 and I may have to publish one notification every 2 - 3 seconds. Both the server and client are built using .Net and WCF.
Given these requirements I have built a set of WCF services which will be run on a load balanced server cluster. The Instance context mode is Per Call and there is no need for sessions etc.
I am currently using BasicHttpBinding. Will TCP binding be better? Does it run on IIS 5 or 6? If not why?
What configuration for serialization can work best?
What are the things I need to do to make sure I get maximum performance?
Edit - Adding more information based on some of the responses -
I host a small WCF service in the client process using manual hosting. The server just calls this service on each client to push the data to all of them.
Firstly have you considered using messaging for what you are trying to achieve?
In answer to will TCP binding work better than BasicHttpBinding- almost certainly yes. If you want to use TCP, you can't use IIS- look into WAS with Windows Server 2008. If you're stuck with Windows Server 2003, then you'll have to host in a windows service instead.
You've made a good choice by choosing per call- this is the preferred instance management mode for creating scalable WCF services.
Edit:
Now you've update your question, I recommend you take a look at IDesign's Pub/Sub framework if you want to stick with WCF. I'd also look at Pub/Sub with MSMQ in WCF and also with "Vanilla" products such as Tibco RV.
If you need pushing data from service to clients you need sessions and you need duplex binding - NetTcpBinding or WSDualHttpBinding. It will not work with BasicHttpBinding because it allows only pulling data (client pools the service for changes). Push data means tha service sends data to clients when needed.
NetTcpBinding always crete session. It can't be hosted in IIS 6 or older. NetTcpBinding is allowed only in Windows Activation Service (WAS) which is extension of IIS 7.x. For older systems you need self hosting = windows service.
Edit:
Based on your description you need Publish-Subscribe message exchange pattern.
Just a technology update, now that .NET 4.0 is out.
I write an application that communicates to the server through what is basically a message bus (instead of method calls). This is based on the internal architecture of the application (which is multi threaded, passing the messages around).
There are a limited number of messages to go from the client to the server, quite a lot more from the server to the client. Most of those can be handled via a separate specialized mechanism, but at the end we talk of possibly 10-100 small messages per second going from the server to the client.
The client is supposed to operate under "internet conditions". THis means possibly home end users behind standard NAT devices (i.e. typical DSL routers) - a firewalled secure and thus "open" network can not be assumed.
I want to have as little latency and as little overhad for the communication as possible.
What is the technologally best way to handle the message bus callback? I Have no problem regularly calling to the server for message delivery if something needs to be sent...
...but what are my options to handle the messagtes from the server to the client?
WsDualHttp does work how? Especially under a NAT scenario?
Just as a note: polling is most likely out - the main problem here is that I would have a significant overhead OR a significant delay, both aren ot really wanted. Technically I would love some sort of streaming appraoch, where the server can write messags to a stream while he generates them and they get sent to the client as they come. Not esure this is doable with WCF, though (if not, I may acutally decide to handle the whole message part outside of WCF and just do control / login / setup / destruction via WCF).
For bidirectional communications, your best bet is NetTcpBinding, rather than the http bindings, if they're available.
This has the advantage of only requiring that the client can initiate a connection with the server.
I would go with Windows Azure Service Bus. See my answer in the following question:
WCF, 4.0, Bidirectional
Take a look at Windows AppFabric, good place to start is Here. It fundamentally wraps up WCF and WF into an application server, with WCF activation supported through WAS. Its where I would host this type of app. It offerd full duplex connection orientated, p2p or sessions between client and server. Don't confuse the Windows appfabric with Azure appfabric, (formely called Azure Service Bus).
As regards bindings above, both NetTcpBinding and WsDualHttp offer callbacks, but the ws binding you get a lot for your cash, especially if it's a mixed programming environment and you have to flatten the wsdl to make interop work. I also think that WsDual is easier on routers traversal, although I understand talking to friends, that Windows AppFabric mitigates this, with new Relay Services, (which i've not seen, and I think have now been renamed).
Hope that helps.
I need to know if Windows Communication Foundations (WCF) can completely and easly help to solve the next scenario:
I need a server program which
constantly receives events that,
according to the content of the
signal, helps to trigger one or many
processes; this server program will
run as a Windows Service.
These events will be generated as
signals from many client WPF
programs and so, can be enqueued.
These events will be generated
according to the results of a timer
also.
The communication between the client
and the server will be using an
exclusive port.
For security reasons the data
communication using the exclusive
port will need to be encrypted.
Finally, The clients will need to
monitor the results of the programa
execution.
If the answer is yes, please try to indicate me which libraries/classes should I consider for points:
1) The event management
2) The enqueue process
4) The setting, opening, use and closing of the port
5) The encryption process
6) Monitoring of the server program execution from the client.
Many, many thanks.
Rather than writing a Windows Service program from scratch, which will need to handle multithreaded queueing of incoming messages, why not make the server a web service? That way, IIS can worry about receiving, queueing, etc. and you can just write the code to process the requests.
From your description, I think a WCF service hosted in a NT Service seems like a great fit.
1) I need a server program which constantly receives events that,
Not a problem at all, the NT service will be up and running at all times, even without anyone being logged on.
2) These events will be generated as signals from many client WPF programs and so, can be enqueued.
Again, no problem for a WCF service - you can create a http, a net.tcp, a MSMQ queue endpoint - all in a single service, really. You get all the flexibility you might need.
4) The communication between the client and the server will be using an exclusive port.
Works just fine - if you self-host the WCF service in a NT service, you can completely control the endpoint addresses.
5) For security reasons the data communication using the exclusive port will need to be encrypted.
All WCF communication is encrypted by default, unless you turn it off.
6) Finally, The clients will need to monitor the results of the programa execution.
Again - not a problem.
For a MSMQ queue, you can create a number of response queues that clients can listen on. For HTTP or NetTCP, you can create a response message (if the processing is very quick) or create a "check for status" operation that allows clients to check for statuses. Or you can mix and match as needed.
All in all, I am convinced WCF will serve you very well indeed !