All ,
I have a doubt on the Request response pattern... Assume the following is my scenario
1.I have a service running on Windows Azure. This service can be called by users to execute a command.
2.I have a client applications that is running on my intranet. This client application will execute the command . The computer in which the client application is running is connected to internet , but does not have a static IP i.e machine cannot be accessed directly via the internet
3.I am planning to use Azure Service Bus through which my service on Windows Azure can communicate with the client application to execute....
In this scenario, can i use Request/response messaging i.e can the service post a message and expect a response from the client
OR
Should i use command queue for each client , the Service will push the command to be executed on a queue , the client will poll the queue and execute a command
Any help is appreciated
Since you are using WCF (based on the tag), you should consider using Service Bus Relay calling the WCF service asynchronously.
I assume you want to use Relaybinding here, using WCF.
Your web service (which is behind NAT, firewall devices, etc) is only opening outbound connections in that case. The service is listening on a registered endpoint in the cloud (that is accessible for him, because of credentials and protocol). All incoming service calls are sent over that port/socket. The response will then be sent back over the outgoing port again.
If the IP Address of your service changes, it wil register itself again (by listening on the same registered endpoint) and you can reach that service transparantly.
Another way you can achieve request/response in an asynchronous fashion, is through queues. This does not require any open connection between your client and your service and can happen fully asynchronous. This can be achieved by sending a message to the request queue for your specific service (with a Correlation Id). And when that service has processed that message, it can send the response to the response queue of your application, using sessions. A good example of this pattern can be found on Alan Smith's blog: http://www.cloudcasts.net/devguide/Default.aspx?id=13051
Related
I have system like this:
Windows service (WCF, data/events) <-> Web app <-> Web client
I need simultaneous response for clients requests. I have some events from service for clients too. So duplex channel is the way to go. But I need high throughput, because clients calls simultaneously.
Request/reply approach
In order not to serialize channel requests I need more channels for parallel calls, right? But how to handle callback channel then? Ho to keep it still open for receiving events, even on channel errors?
OneWay approach
On channel should be enough (no waiting for data preparation), but how to link data sent to callback with original request, to be able to compose response for client?
What is the way to go? Thank you.
In a simple case, when a web client sends a request to the web app, and web app (possibly) sends a request(s) to WCF service, there's no need in duplex binding at all.
As for events, raised by the service to be fired in Web client, I'd suggest to use a message broker which supports WebSockets - for example RabbitMQ. It has a plugin compatible with WebSockets and WCF binding.
Putting things together, one can create a RabbitMQ server, which accepts messages from WCF service and sends it to Web client, which subscribes to the event feed from Javascript.
Is it possible a service to call client after 4 -5 days when client is offline? e.g.
1. The client request some reports through service.
2. Service updates database with client request.
3. Offline work is done on the request
4. Report is uploaded to the database.
Can we service call its client and send report as soon as report is uploaded to database?
Can WCF duplex service be used to call client when client is offline?
Yes. WCF can be configured to use MSMQ as a transport. MSMQ is the only WCF transport that allows for all three:
disconnected scenarios
resume when computer becomes online and
optionally provide a level of guaranteed delivery
MSDN:
If you need to support disconnected queuing, use netMsmqBinding. Queuing is provided by using Microsoft Message Queuing (MSMQ) as a transport, which enables support for disconnected operations, failure isolation, and load leveling. more...
Essentially you invoke a WCF method (send a MSMQ message) and it will be delivered when the computer comes on-line again. Assuming you have set the appropriate expiration options.
I am using a client server application in which client send request to server in request queue, server receive this request object from queue process it and send response in response queue which is received by client application. I want same functionality in wcf service and client so whether I need to create two different end points for both msmq and if yes than how same client will work with both endpoints.
You should not think of it as strictly a client server application.
You do have a request originator referred to as client and a request processor referred to as Server,
but when thinking WCF- client is the one sending the message, server is the one receiving. Meaning that in WCf terms, at first your client is really a classic "client" and the server is really a classic "server". But when you get to the point after the original request is processed and needs to be sent back- the roles are reversed! the server becomes a WCf client and the client becomes a WCf server.
What this means is that you processes need to expose a separate endpoint for each other. The server listens on a certain EP for incoming messages (requests), and the client listens on a certain EP for incoming messages (responses).
Hope this clarifies things a bit.
I've followed the instructions from https://github.com/SignalR/SignalR/wiki/Hubs
entitled "Broadcasting over a Hub from outside of a Hub".
I got this method working from within an MVC Action in the same project. Requesting the Action sends the update to connected clients.
My problem is that I need to be able to send updates from another project, in particular a WCF Web Services project. My app has an API and a web component and when API users make calls that change things, these updates need to be pushed out to the Web clients via SignalR. And calling a web service with the same code as my Test Action doesn't work.
I also tried the same code inside an nunit unit test that didn't work either.
What do I need to do to make this same method described on the Wiki work for a WCF Project?
The easiest solution is probably to provide an API on your Web Application (use MVC or the new WebAPI) that broadcasts to all connected clients. Any other application (an NT Service, an NUnit test, ...) can call that API if it wants to send a message to the clients.
You can't expect SignalR to do anything if you aren't hosting a Hub either in a Web Application running under IIS, or another application hosting it directly.
If you need two-way communication from your separate application to your clients then simply make your application into a SignalR client too and have it communicate via the Web Application hosted SignalR to the clients and have it listen to messages from them too.
For example, here's how I have configured a complex Service + WebSite + Clients solution (ignore the purple for now):
The Live Web Server allows NT Services to connect and create SignalR Groups. NT Services send to those groups. Web browsers connect to a group and receive messages send to that group. In effect the middle box becomes a pubsubhub.
I cannot get exactly what you aim. But if I understood correctly you're trying to send some kind of notifications raised inside WCF services to SignalR clients.
If that's the case; I can suggest you my approach:
I have some WCF services and a SignalR hub in the same application server. IMHO, the best way to communicate WCF with SignalR hub is by using MSMQ.
When a notification occurs inside a WCF service, it puts the notification payload into MSMQ.
On the other end, SignalR hub listens the same queue. When a message put into the queue, it gets the content and broadcasts to the hub clients. Very easy and straightforward. No extra service/hub call at the server side.
SignalR hub can listen for new queue items by using System.Messaging.MessageQueue#ReceiveCompleted method. When this event raised, SignalR hub gets the queue item and broadcasts to its clients.
Here is my scenario, and it is causing us a considerable amount of grief at the moment:
We have a vendor web service which provides base level telephony functionality. This service has a SOAP api, which we are leveraging to build up a custom UI that is integrated into our in house web apps. The api functions on 2 levels. You make standard client calls into the service to initiate actions, such as Login, Place Call, Hang Up, etc. On a different thread, the service sends events back to the client to alert the user of things that are occurring on the system (agent successfully logged in, call was disconnected, etc).
I implemented a WCF service to sit between the web server and the vendor service. This WCF service operates in duplex mode, establishing a 2 way connection with the web server. The web server makes outbound calls to the WCF service, which routes them to the vendor's web service. Events are received back to the WCF service, which passes them onto the web server via a callback channel on the WCF client. As events are received on the web server, they are placed into a hash table with the user's name as the key, and a .NET queue as the value to hold the event. Each event is enqueued to the agent who owns it.
On a 2 second interval, the web page polls the web server via an ajax request to get new events for the logged in user. It hits the hash table for the user key, dequeues any events that are present, and serializes them back up to the web page. From there, they are processed in order and appropriate messages are displayed to the user.
This implementation performs well in a single user scenario. The second I put more than 1 user on the system, I start getting frequent timeouts with the following CommunicationException:
A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond
We are running Windows Server 2008 R2 both servers. Both the web app and WCF service are running on .NET 3.5. The WCF service is running under the net.tcp protocol in duplex mode. The web app is ASP.NET MVC 2.
Has anyone dealt with anything like this scenario? Is there a more efficient way (or a widely accepted pattern) to implement this?
EDIT: One thing I forgot to mention - my thought is that the increased traffic (adding additional users) with only 1 dedicated callback channel is causing locking, which then triggers the timeout. There can be up to 10 consecutive callbacks from the service within any 5 second interval.