I have a lot of client programs and one service.
This Client programs communicate with the server with http channel with WCF.
The clients have dynamic IP.
They are online 24h/day.
I need the following:
The server should notify all the clients in 3 min interval. If the client is new (started in the moment), is should notify it immediately.
But because the clients have dynamic IP and they are working 24h/day and sometimes the connection is unstable, is it good idea to use wcf duplex?
What happens when the connection goes down? Will it automatically recover?
Is is good idea to use remote MSMQ for this type of notification ?
Regards,
WCF duplex is very resource hungry and per rule of thumb you should not use more than 10. There is a lot of overhead involved with duplex channels. Also there is not auto-recover.
If you know the interval of 3 minutes and you want the client to get information when it starts why not let the client poll the information from the server?
When the connection goes down the callback will throw an exception and the channel will close.
I am not sure MSMQ will work for you unless each client will create an MSMQ queue for you and you push messages to each one of them. Again with an unreliable connection it will not help. I don't think you can "push" the data if you loose the connection to a client, client goes off-line or changes an IP without notifying your system.
Related
I have a back end system that drops events to my system. It is critical that these events don't get lost (I work for a health care company and lost info can impact a patient's care).
I would like to make this system drop it's data into NServiceBus so that it can be published to subscribers that need it. However, my server that is dropping these messages is an AIX machine, so it can't run .NET Code.
This system can send the messages via a lot of standard protocol and communication types (TCP, WSDL Based Services, Call A Database Sproc, etc).
One option I have considered is to setup a WCF service that the AIX mainframe will call. I can then have my WCF service make the call to NServiceBus.
But the events sent per minute of this back end service can at times be fairly high (about 500 messages per minute). I am worried that WCF is not up to this, while NService bus says it can handle 1000 messages per second. Am also worried about data loss in the event of a downtime. NserviceBus claims it is not going to loose any data.
Am I wrong? Is WCF going to be just fine? Or am I making a weak link in the chain?
Is there a way I can use an established protocol to add items directly to an NServiceBus Queue?
Or should I just write my own .NET app that will allow NServiceBus to use a TCP connection?
Note: Because these messages are critical, the message must be acknowledged or the server will keep sending it.
I would take a look at the WCF integration that comes right out of the box. The WCF service is contained within the same host as NSB. The integration does nothing more than just push the message onto the queue, so I don't think you'll have a throughput issue. Seeing that this is critical data, I would suggest clustering the service. The other option would be to install 2 or more instances of the service on different machines and load balance the HTTP calls across both. In essence you would have 1 logical Publisher with 2 physical components doing the publishing.
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.
I have a multi-gui one-service architecture (i implement both, service and client) (using .net 3.5, c#, windows application/service).
whats the best practice to update the guis? i know duplex communication, but if the client doesn't send any requests for some time, the channel is closed! increasing the timeout is not the best solution...?!
Regards
Marcus
The GUIs are sending commands to the service per TCP Duplex. Each time, one GUI is changing some things, the other guis have to be informed about the changes, happend to the service.
first solution: the guis can poll each x seconds the service to ask: are there updates?
but i don't really like this solution. each time a change happend, the service send an "gui you have to update" via callback to each gui. but mayby all the channels are not open anymore...
hope this helps to understand (sorry for my very bad english)
If you want architecture where client registers to the service and service pushes data changes to clients immediately when changes happen than duplex binding is the solution. Otherwise don't use duplex binding.
If you don't like the idea of increasing connection timeout you can always implement your own keep alive mechanism. Client will continue sending some keep alive messages to the service in predefined interval so connection will be still opened.
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 !
I like using WCF callbacks when I can because to me it is better than the client having to poll the server and its more real time than polling. The question I have is when I subscribe to a WCF service event is there any kind of heart beat that keeps the connection alive between the client and the server. I starting to think that there is not because when the server goes away the subscription is lost and the client does not throw an exception (could be the exception is be swallowed by the WCF runtime). Same is true for the server, when the client goes away and the server attempts to invoke the callback and exception is throw. Any thoughts?
Thanks
There is a good short description of the Duplex contract (WCF callbacks) in this link. The duplex contract is basically two one-way channels and there is no implied message correlation. You are right, there are no "heartbeat" messages are involved, only the normal wsHTTP handshaking traffic occurs when making a duplex call.
I fired up the HTTP traffic sniffer called Fiddler2 (an unsupported Microsoft tool) to verify the session traffic. Didn't see any under-the-hood HTTP "heartbeat" communication occurring during and after the service calls. I left the client running for a good while. Good question, it got me digging a bit.
I went ahead and created a recurring heartbeat to the subscribed clients (basically a call to a function they're hosting).
I've run this for hours and it works, this helps ensure the connection.