I need to implement a WCF service which in turn calls a third party web service for some XML result.The client calls come from windows WF apps & will be on separate processes.But for client calls coming from the same parentID, there should be only one call per ParentID, i will explain,
MainID1\SubID1 & MainID1\SubID1 on different processes calls the WCF service for result & if MainID1\SubID1 was the first to make the call, MainID1\SubID2 should wait until the first call is completed.The idea is to prevent unnecessary call to the third party web service, if we get the expected results already from the first call.
But if there are MainID2\SubID1,MainID2\SubID2,MainID2\SubID3 calls, that should be served by a different instance of the WCF service.
In short:
Related requests should be processed sequentially by one instance of WCF service
Unrelated requests should be processed by separate instance
Sorry, if haven't made myself clear, not at the liberty to use the actual business terms(which might have helped to define related & unrelated clients better).
Is this really possible?
Yes, you can do this, but it will not be trivial. Basically you need another component between your WCF Web Service and the 3rd Party service which handles the throttling/locking behavior which you describe. That component needs to create a object for each unique combination and then use that as a lock guard around the outbound call.
Realize that this is clearly multi-threaded development, making it hard to test, and prone to errors if you're not experienced with the ideas around it. You'll want to ensure you're doing double-checked locking whenever you take out a lock.
Related
The project I'm currently working on includes a server that receives C# scripts (partial code) from clients, wraps it to create a complete class, compiles it then load it into a separate AppDomain for execution.
A task (currently running script) can send feedback to the user at any point of it's execution, as defined in the script by the user. And possibly the task might wait for a response from the user (currently assuming it's only right after having sent feedback). And the user might, at any moment, decide to kill a task.
The server is implemented as a Windows Service hosting a WCF Service Library.
As I don't want to overcomplicate the client to make it communicate directly with the dynamically created AppDomains, the (partial) solution that I considered after some research was hosting a second WCF service with named pipe binding to make the dynamic AppDomains use it as a relay between them and the client facing WCF service.
My issue is that now I can't think of a clean way to have the two WCF services interact.
My ideas are:
Having them maintain direct references to each other:
Seeing as Normally both of the services are singletons it shouldn't be hard to do.
But that would be a pain to maintain in the case one of them fails and needs to be restarted. (I'm still new to WCF so I have no idea how common that is, but it's still an issue to consider. I think.)
Introducing some sort of a "message queue" (or two, one for each direction) with properties that can be set and subscribed to. Thus when one service sets a property an event will be triggered in the second. But that feels somewhat hacky to me, even though I can't really think of any clear issues.
I could really use some expert input on what I'm trying to accomplish, be it opinions on my thoughts or new ideas. Even if that involves rethinking the architecture. This project is still in an early enough stage to afford some rework, as long as there is enough reason to do that of course.
Since I've put lots of efforts (read: 2 minutes on paint) to prepare a quick (read: useless) schema of the system, I'll link it here since I don't have the reputation to post images:
Link to schema
Edit:
As I now have the reputation thanks to an upvote:
Still after rereading my question, I feel that perhaps I have been looking at this issue from a too narrow perspective by thinking of the services as something more special than ordinary classes. The more I think about it the more I feel that the observer pattern is probably the best approach to take.
Just for the record, and to avoid leaving my (silly) question unanswered, I've realised that I was looking at this too narrowly by trying to find a solution specific to WCF services.
And finally I ended up using a variation of the observer pattern (based on the IObservable<T>Interface).
I came across the same issue. The way I handled a duplex communication between the two servers is as following:
For each process (AppDomain Seperated Task) create a pair of WCF services. Both services have their Instancing set to PerSession (no need for singleton which may cause problems in the long run like disconnect). This means the Client will be communicating for each process (AppDomain Separated Task) with two distinct Service instances or a service pair (i.e. Service1 and Service2).
We want a duplex communication in between these two services, which means that both can communicate with the other and pass data (in the form of a DataContract class object).
For this:
1- Declare two services (i.e. in a separate class library) and host them (self hosting or else).
2- Create your DataContract class and add any property, collection, enum etc. as you like. Both services must have a get-set property for this class.
3- In the same class library (where the Service1 and 2 classes reside), create another class. This class will act as a depository for the Service pair instances. It has a static List in order to register the service pair instances (you can identify each service with a GUID).
4- We setup the client proxy using svcUtil.exe (or by code). When the client makes a service request, a service (i.e. service1) will be created by the WCF. At service1, create or launch the process (App Domain Separated Task) as client2 and at its constructor create the Service2 proxy by code.
5- Initialize the Service2 instance (i.e. by a call to the service2) and register the service pair instances at static list of the depository (so that it can be retrieved later for duplex communication). Now we have both service instances and both of them are registered as a pair into a static list.
6- Start communication between both services by making a call from Client1 proxy.
7- At Service1 call method, retrieve the service pair from the static list. Deep copy (DeepClone) the Datacontract class object from Service1 to the Service2 using the get-set property mentioned at (2). (Note that you can use one of the many Deep Clone libraries from Nuget like DeepCloner).
8- Make a call back from Service2. Client2 now has the identical DataContract class property values as Client1
9- Repeat steps 6-8 for Client2 proxy for Service2-Service1 communication.
So bear with me, i am new at MVC and WCF. I already have a set of services (WCF) that exposes my BLL and I am trying to consume those from my MVC.net web application but i am unsure on how to perform security operations here.
These are my app requirements:
Be able to consume WCF services using different credentials for every user on the web application
My BLL (WCF) needs to know what consumer is calling it (right now I only have the MVC app but i am planning to add iOS and Andriod calls to it, so later on i will add REST services to the WCF endpoints) Is there any design pattern for this out there? (or should i just use the soap header to include the caller ID? should i use some sort of caller secret or something?)
I need a security mechanism like Tokens or something so I dont have to pass the username and password on every call of the service method (WCF)
What i have so far:
WCF uses a certificate and and with a custom username validator.
I have manually coded proxies using the contract interfaces instead of generated proxies: But I hate the fact that i have to validate username and password every time a call is made to a WCF service. How in heaven can i use Tokens here? like to know if a given token sent on the soap header is valid or not yet expired? i have searched a lot and no tutorial/code/example is clear enough for me to actually start coding that ;(
I am trying to cache the ChannelFactory but should I? i mean, i will need to cache a channer factory per logged in user per contract ;( is that ok? what can i do here?
Thanks in advance!
Should you cache the ChannelFactory per user per contract?
It depends. There are a couple of considerations. Instantiating a channel factory could take up to 70ms. If you are doing this repeatedly, you will see a noticeable performance hit if you are not caching the ChannelFactory and instantiating one (or more) each time a user makes a http request to your MVC app that results in controller actions calling web services. This would indicate that caching the channelFactory would be beneficial for speed.
On the other hand, depending on the number of users you have, if you are caching a lot of channel factories (in a static dictionary for example), you are going to start to use a non-trivial amount of memory - this may become an issue for you.
You have to decide if the cost of instantiating channel factories on the fly (and correctly closing / aborting them and their contained channels) is too high a price vs increasing memory utilisation in the application pool hosting your MVC app.
Either way, I strongly advise to profile your app before you deploy to production.
I have a number of WCF Services which are called for a certain function from an ASP.NET MVC application.
The MVC app calls Contract-Service (WCF Service)
Contract-Service during its processing calls Contract-Buy-Service (WCF
Service)
Contract-Buy-Service calls SAM-Utility-Service (WCF Service)
When I run my TDD test cases from Contract-Buy-Service, it works perfectly fine. Because the call goes from Contract-Buy-Service to SAM-Utility-Service. But when the call goes from
Contract-Service => Contract-Buy-Service => SAM-Utility-Service
I always get the error that the endpoint for SAM-Utility-Service is not found in the config.
There is a service reference for SAM-Utility-Service in both the contract-buy-service and contract-service. I have checked that the service is hosted and is up and running. I can get the WSDL when I try to view through browser.
Can someone tell me why the service call does not go through multiple layers or am I doing something wrong here?
Thanks!
To begin with, I don't believe the Contract-Service should need a service reference or any knowledge of the SAM-Utility-Service. Unless it needs to directly communicate with that service for some other operation - in which case I'd suggest another service endpoint anyway - it shouldn't know about what the Contract-Buy-Service is doing. This is leading to tighter coupling of your services which removes one of the major benefits of service-orientation.
The cause of your problem could be a number of things (as is always the way with WCF). However I've had similar problems to this caused by bad choice, incorrect use or misalignment of transactions.
Consider that, for example, Contract-Service and Contract-Buy-Service participate in a transaction. SAM-Utility-Service may also require a transaction, but requires a new transaction. If this second transaction doesn't participate in the first transaction correctly, then the first transaction may not allow it to commit or may not commit itself.
One first step could be to get all three working in concert without any transactions.
We are migrating set of WSE services to WCF platform.
The new WCF services are called over secured HTTP. (https)
I want to invoke an operation contract of one WCF service from another. Both the services are mostly hosted in the same IIS, but they can be on separate IIS server.
Do I need to take care of some things (which i obviously do not know at present) in this scenario?
Is there any special calling mechanism in this case?
Does calling mechanism change when call is synchronous and when it is asynchronous?
Can you suggest some type of binding which is readily available in this case?
1.) If the services are on the same box, use named pipes, unless you have any compelling reason not to, to communicate with each other. While WCF proper doesn't care about what you're doing as long as the address, binding and contract all match up (see what I did there?), .NET will when it comes to making network connections. The fewer you use, the better. (see http://msdn.microsoft.com/en-us/library/fb6y0fyc.aspx for more details)
2.) As stated in #1, if they're talking on the same box, use named pipes unless there's a good reason not to.
3.) Can you provide a little more detail on what you mean by this or what you're planning on doing? A lot of this is built out for you, so assuming you're familiar with implementing async methods and using async callbacks, the short answer is yes, it's different than calling an operation synchronously, but that's to be expected. Or do you mean IsOneWay = true? If that's the case, the calling mechanism is the same but there can be a number of other gotchas (e.g. faults)
4.) Named Pipes on the same box, BasicHttp otherwise (unless you need any of the additional features from WS).
but they can be on separate IIS server
In this case, you either can't use Windows authentication (if you were using it) or you have to set up some special delegates stuff on the domain to make it work. Windows Authentication won't "hop" between different servers. Here's some info on that, there's a lot of reading out there on the subject.
If they stay on the same server or you're not using Windows authentication, then it shouldn't be a problem.
Does calling mechanism change when call is synchronous and when it is
asynchronous?
Shouldn't matter, it's all the same on the service end. I will say that if the client calls X and X calls Y, X might as well call Y synchronously because it can't return to the client until Y is done anyway. (If X calls Y and Z, then X making async calls may make more sense.)
Can you suggest some type of binding which is readily available in
this case?
If you were using WSE before, then BasicHttpBinding is going to be the one closest to what you were doing and will look pretty familiar in what it outputs. It's also the simplest one to work with.
There shouldn't be anything special needed just because a WCF service method calls another WCF service. A WCF service doesn't "care" what other application types are calling its methods so long as they use the correct service contract, data contract, endpoint, and binding settings.
Just make sure that both service methods return promptly, and don't cause execution to block for long periods of time.
Using visual studio 2010 RC/.Net 4.0
I have a wcf workflow service with three receive activities defined, basically StartProcessing, StopProcessing, and GetProcessingStatus. This is a long running service that continues to poll an external service for data once StartProcessing is called, until StopProcessing is called.
My problem is with figuring out how to use correlation to ensure that all calls into the service call the same instance of the workflow. I am trying to avoid requiring any sort of instance id be required to be passed back in to subsequent calls to the service. In a nutshell, I would like the workflow being executed to be a singleton, and ensure that all receive activities operate on the same instance. How do I go about doing this?
You can correlate on a constant for example. Edit the XPath in query correlation to return the number 1 for example.
I think that what you want is impossible, you need to correlate, WWF does not know how to execute it. If two parallel calls are received they will use the same object with unexpected results.
In wcf it could be possible, you can set a session in the client or you could manage wcf object creation, but in WWF I think you even don't have that options.