I'm new to WCF and need some assistance with architecture for the following solution:
I want to create a WCF Service that hosts a FileSystemWatcher. This service must watch a series of folders on the machine and when a file is placed in a folder or is renamed I need this WCF service to 'Publish' an event.
Another WCF service must then 'Subscribe' to this event and do some processing.
The basic idea is that there is one service to monitor a predetermined set of directories, whilst an appropriate service gets notified that there are files available for processing.
So my questions are :-
1. Regarding the FileSystemWatcher WCF Service, I want to host it in AppFabric but am not sure exactly how this is going to work. I.E. When this service is deployed to the server I want the appropriate FileSystemWatcher object to be called and stay 'on' and monitor folders indefinately. Can WCF do this in this manner or is this a better candidate for a Windows Service
2. Can one WCF service publish events and another WCF service subscribe to these events and how? All WCF services hosted inside AppFabric?
WCF is a communication framework that can be used to expose or consume SOAP/REST services. A Windows Service is one way of hosting such applications. WAS/IIS and self-hosting are other methods. A Windows Service provides greater control of service startup/shutdown, which seems relevant to your scenario.Windows Server AppFabric improves some of the control over applications lifecycle hosted in WAS/IIS, but it is still a fundamentally different hosting choice to a Windows Service.
As far as I know WCF has no inbuilt event publishing capability (I assume you're referring to the publish/subscribe pattern). However, you can implement such a pattern using WCF duplex channels. There is no restriction on an application concurrently acting as 'server' and 'client'.
Related
I have an application that places messages on MSMQ, than I have a WCF service that I want to automatically read these messages from MSMQ.
I do not want to trigger my WCF service but I want it to be notified whenever a message is pushed on MSMQ. I have found some stuff related to WAS and netMSMQBinding, but the details seems a little unclear about automatic notifications from MSMQ to WCF.
Any help/direction in this regard? Thanks.
What is it that you're trying to achieve?
There is really no such thing as "be notified when a message is pushed on MSMQ". MSMQ uses a pull model to retrieve messages from a queue, so there always needs to exist some kind of "listener" that reads messages from the queue and processes them.
In this case, this "listener" is provided by the WCF NetMsmq or MsmqIntegration bindings automatically, so the programming model for a WCF service that is exposed over MSMQ is just like that of a regular one-way service.
As you state, you can either host that WCF service using your own custom host (such as a Windows service), or, in many cases, the preferred method will be to host that service in IIS 7.X/8.X through WAS.
The following sample shows how to host an MSMQ service in WAS: http://msdn.microsoft.com/en-us/library/ms752246(v=vs.110).aspx
Notice that you do need some specific configuration in IIS to be able to host non-HTTP services, which includes enabling the "Non-HTTP Service Activation" feature. The following articles will be useful to get this done:
http://blogs.msdn.com/b/tomholl/archive/2008/07/12/msmq-wcf-and-iis-getting-them-to-play-nice-part-1.aspx
http://blogs.msdn.com/b/tomholl/archive/2008/07/13/msmq-wcf-and-iis-getting-them-to-play-nice-part-2.aspx
http://blogs.msdn.com/b/tomholl/archive/2008/07/14/msmq-wcf-and-iis-getting-them-to-play-nice-part-3.aspx
http://blogs.msdn.com/b/tomholl/archive/2008/05/17/building-a-pub-sub-message-bus-with-wcf-and-msmq.aspx
I've gone through some tutorials on creating a WCF service. I'm using Visual Studio 2012. I got a very simple WCF Service Library (vb.net) and Windows Application (vb.net) communicating via WCF. That's a start.
However, my project requires I do the following:
My Windows Service - This is already an application that has it's tasks.
My Application - This is an application that is already developed as well.
I need the service to talk to the application. The service will need to send the following information to the windows application:
Status Updates
Metric Information (mostly integers for counts)
I need the application to send information to the service. It would need to send:
Reload Configuration command
Should be relatively simple, but I've never worked with WCF until today. So I have some questions...
Do I need to re-work my current windows service into a WCF Service?
Since it won't be in IIS, do I also create a WCF Service Library or do I roll this into the windows service somehow?
What is the best way to set up the different types of communication? (i.e., sending over specific metrics and reload commands)
Probably the main question is what components, in addition to my current windows service and application, will I need to make this work?
I hope that was clear :( I think I'm confusing it all... but I hope not
Your Windows service can host the WCF service. Similarly, if you want, your application can host a WCF service. The application could talk to the WCF service in the Windows Service, and the Windows Service's WCF could talk to the one in the application. Depending on the nature of the communication, you could also just use a callback channel to permit the Windows Service's WCF to call back to the application.
I suppose you should configure your WCF windows service to use named pipes. If your windows service is already built then the easiest way to do it would be to build another one as a WCF windows service and wrap the already existing functionality.
Hope I helped!
It is my understanding that a WCF service configured for net.msmq will not run as an HttpApplication when hosted in IIS/WAS, which means you don't get the events in Global (Application_Start being the important one). Am I correct in this regard?
Does using Windows Server AppFabric to auto-start the service hit the service over HTTP, causing the Application_Start event to fire? If so, is this reliable?
I guess my real question is, where is the "proper" place for initialization code for a non-HTTP WCF service?
Particularly (since the right place may be different for different stuff):
IoC registrations
log4net initialization
Verifying the MSMQ queue exists locally (as Juval Lowy suggests in his WCF book)
Follow-on question: Do the events in a custom IServiceBehavior fire on every request or only once at startup? What about ServiceHost.OnOpening() - every request or only once at startup? (My testing shows it's only once, but does anyone know where the WCF "lifecycle" is documented, because I can't seem to find it anywhere.)
I can't verify that WCF services hosted in IIS/WAS can't be configured to support Application_Start but it is not required to do what you want. I'd recommend you create a custom ServiceHost in conjunction with a custom ServiceHostFactory (for WAS). This approach is documented in an MSDN article and this blog post. Using this approach, you can host your service in IIS/WAS, a Windows Service or a console app because the initialization process will be the same.
I am developing a WCF web service and I used the WCF Service Application template to do that.
Does creating a "WCF Service Application" fulfill this requirement?
What are the advantage of creating a WCF Service Library over a WCF Service Application?
A service application includes a website host already setup for you. A service library is a library of services that a host can reference and startup.
If you start with a service library (recommended) you can then choose any host you wish (a windows service, IIS/ASP.NET, or even a console application) and you'd just reference your library from your new host. Choosing a Service Application limits your host to just IIS/ASP.NET (though this might be ok for your purposes, but will limit the protocols you can use).
Edit: Changes in IIS since I wrote this allow for a wider variety of protocols on ASP.NET activated services, so choosing a service application is much less limiting than before.
If all you have is the one project I see only added complexity if you separate for the heck of it. I used a library when I had some particular use cases where I had to host in both a windows service and in IIS.
For IIS you you can move the classes and interfaces to a library but keep your .SVC files in the web project. You must edit the .SVC files to point to the properly qualified classes.
Two weeks ago I needed a way to communicate a wcf service with a windows service running on the same computer. The windows service had to get data from a external source and share it with the wcf service (hosted in IIS) who had to give it when a client made a request. I chose to do that with ipc.
I done it and now the windows service is the ipc server and the wcf service is the ipc client. This goes well but I think I made a mistake doing this because to make it run right the windows service must to be executed with the ASPNET account, for this the ASPNET password account must be assigned and when I do that the IIS does not work correctly.
I am thinking on different alternatives, but in all of them the problem persists. Some ideas?
Edit:
What I needed was a system that made public, in a web service hosted in IIS, data gotten through telnet from another old system, what is a little unstable. How the response of this second system was slow I chose to put a process (the windows service) between the web service and the old system. The windows service had to save the data collected from the old system and when the wcf service asked it give it all at once through ipc.
Why does the windows service need to run as the ASPNET user? Is that because you're using an IPC connection that requires authentication from the caller?
Another alternative (if you have control over the windows-service code) would be to make that a WCF service as well (using a ServiceHost in the windows service). The IIS service could connect to the windows service using a NetTcp or NetNamedPipe binding if you need the IPC-like performance.
Why not just create another account with the same permission set of the ASPNET user which both the WCF service and your other service run under? That way, you have control over the password.
Ideally, the windows service should run as a WCF service, that way its easy for the client to communicate with it.
The next question is weather the 'client' needs to be a WCF service. If this client needs to serve other applications then it is appropriate, otherwise it may not be nessesary. I don't know enough about your system, so its up to you to decide what's best!