I have encountered a strange issue while working with SignalR. It may be something I am doing wrong or an incorrect expectation on my part. I have posted the example code an issue description on git
https://github.com/boblautenbach/SignalRGroups
Thanks
-bob
OK, So I did some additional research. I found a SO q/a SignalR lost messages if IIS configure with more than 1 worker process that mentioned the same concerns and even though it wasn't related Azure, it was very relevant. If you have more than one instance of your Signalr hub Azure Web App, which can be set as seen below, then you will run into the issue I mentioned. Essentially, client connections made to instance A will not see instance B connections. If you do need more that one instance of your Hub, you will need to implement one of the scale-out options here http://www.asp.net/signalr/overview/performance/scaleout-in-signalr. I test this using the Service Bus scale-out option and it worked great (my site currently has 2 instances).
Related
Requirement: I need to create a background worker/task that will get data from an external source ( message queue) at certain intervals ( i.e. 10s) and update a database. Need to run non stop 24hrs. An ASP.NET application is placing the data to the message queue.
Possible solutions:
Windows service with timer
Pros: Takes load away from web server
Cons: Separate deployment overhead, Not load balanced
Use one of the methods described here : background task
Pros: No separation deployment required, Can be load balanced - if one server goes down another can pick it up
Cons: Overhead on web server (however, in my case with max 100 concurrent users and seeing the web server resources are under-utilized, I do not think it will be an issue)
Question: What would be a recommended solution and why?
I am looking for a .net based solution.
You shouldn't go with the second option unless there's a really good reason for it. Decoupling your background jobs from your web application brings a number of advantages:
Scalability - It's up to you where to deploy the service. It can share the same server with the web application or you can easily move it to a different server if you see the load going up.
Robustness - If there's a critical bug in either the web application or the service this won't bring the other component down.
Maintanance - Yes, there's a slight overhead as you will have to adjust your deployment process but it's as simple as copying all binaries from the output folder and you will have to do it once only. On the other hand, you won't have to redeploy the application thus brining it down for some time if you just need to fix a small bug in the service.
etc.
Though I recommend you to go with the first option I don't like the idea with timer. There's a much simpler and robust solution. I would implement a WCF service with MSMQ binding as it provides you with a lot of nice features out of the box:
You won't have to implement polling logic. On start up the service will connect to the queue and will sit waiting for new messages.
You can easily use transaction to process queue messages. For example, if there's something wrong with the database and you can't write to it the message which is being processed at the moment won't get lost. This will get back to the queue to be processed later.
You can deploy as many services listening to the same queue as you wish to ensure scalability and availability. WCF will make sure that the same queue message is not processed by more than one service that is if a message is being processed by service A, service B will skip it and get the next available message.
Many other features you can learn about here.
I suggest reading this article for a WCF + MSMQ service sample and see how simple it is to implement one and use the features I mentioned above. As soon as you are done with the WCF service you can easily host it in a windows service.
Hope it helps!
We have a secured & authenticated WCF service which cannot use service references. Thus, we provide the interface for the contracts and open client channel manually.
We have found out that as long we open it once, everything works fine. We can call several methods several times. However, if the channel is closed or just set to a new instance, the Login() (which happens to be required for first step prior to using the service), times out.
To make the matters even more mysterious, this only happens on our production server. If I run the same project locally, I am able to login many times as I want. Consuming the methods inside a web browser (even on a code-behind ASPX page) do not have this problem even with the production server. ONLY when it's a .NET client trying to open a client channel against the production server, do we have this problem.
We are not even sure where to start looking. Any advices would be greatly appreciated.
UPDATE:
As per #Rene's suggestion, we turned on logging on both sides. From client's log, there is a record of error which is basically the same timeout error we already got via the exception. Nothing meaningful. On the server's logs, there are records of service methods being invoked successfully even after 2nd login() and from server's POV, the request is served.
Additionally, I discovered that I could not even reproduce this issue on my machine using same test project to reproduce this problem. This reproduces on my developer's machine. I verified that we were at same version of .NET framework and Visual Studio. It has to be surely a client-side problem. What could be it?
In case anyone else is looking for answer, we finally found it -- the issue is due to the need to set on client's side System.Net.ServicePointManager.DefaultConnectionLimit to some higher value. The default value is 2 but in reality this allows only one proxy to be created and be usable. Setting it to 3 would allow 2 proxies to be created & be used.
I have a web service that is on an internal server. It can be called from any website on our network.
More and more developers are starting to use it. Current probably 20+ pages use this service, and the number is growing fast. I can see a year from now, someone asking what pages are using this service and what methods.
I would like to log the url of the pages that use my web service as the request come in.
It would also be nice to know the method they are calling.I need to do something in such a way, that it does not affect the client web sites.My first thought was that I could write some code in the global.asax.
I have added some code to the Application_BeginRequest to log the request object details, but there does not appear to be anything about the requesting url.
What am I missing? Should I be looking at a different object?
Thanks.
Without disrupting existing users this is going to be difficult. The httpContect.Current.RequestUrl will just return the URL used to call your web service, not which web page called it.
The closest you can do without disrupting existing apps and forcing developers to change them is to grab the HttpContext.Current.Request.UserHostAddress, so you can at least get the IP of the machine calling your service.
Beyond this, what you might want to consider is adding a parameter to your functions for "CallingApp" and then log that in your code. That's pretty much what we did once re realized that we needed to know which apps are calling our service. We actually have an application monitoring service that uses a GUID for every new app we develop, and we pass that GUID to any web service. It[s extra work but to us it was critical because it allows us to know which apps will be affected when we need to perform updates or take the app server down for maintenance.
Edit - added
As a side note, at the point we realized we needed to track this, we had already been using web services for about a year. When faced with the same problem, we created a new set of web services, and included the extra field for the calling app in all of the new services, and then slowly went back and changed the older programs to point to the new services.
IN retrospect, we wish we had known we would need to do this up front because it created a lot of extra work. I'm guessing you'll be facing something similar if you really want to know exactly who is calling your services.
The only thing you can probably retrieve from the consumer is the IP address without changing your interface.
If you can change this you could do this e.g. by adding authentication and logging who is calling what, or by having some simple "token" principle.
However both methods require you to change the interface and therefore break backwards compatibility - which you should never do.
By always ensuring both back and forward compatibility you should not need to know exactly who is calling your service, but only that it is actually used.
#David Stratton
Thanks for your help. I think your suggestions were great. I accually did something very different, after your answer gave me some new ideas.
I should have mentioned that I was generating the web proxy that most of my users were using to make calls against my web service. My client in general do NOT use the proxy that Visual Studio creates.
Here is what did:
I generated my web proxy client again, and added calls to log the httpcontext of the client before every call. Because the proxy is running on the client, he had access to everything I needed. That allowed me to record everything about the client and the specific call they were making. I realize this would not work for most cases. But all of my clients are internal web sites.
It also had the advantage in that the clients did not have to modify their code at all. I just gave them all a new DLL. Problem solved. I get all the tracking data I want, and they did not have to modify their code.
I was stuck trying to solve the problem from the web service's point of view.
I realize that there is still a whole in this implementation, because someone does not have to use my client proxy to call my service. I guess I could force that at some point in the future. For now, they could let Visual Studio genereate a web proxy for my service. However, if they do that I guess I don't care. That is not the recommened way to call my service. I think the only one doing that is an ASP.NET 1.1 web site. When they upgrade, they will probably switch to my generated proxy.
Without implementing some sort of authentication, there isn't a guraenteeted way of knowing exactly who is calling your service - web metrics are the only way you can gauge what volume of traffic is hitting your service.
I'm sure you already know this but the whole point of a web service isn't to know or care who is calling it.
I have successfully used ...
Dim strReferrer As String = HttpContext.Current.Request.UrlReferrer.AbsoluteUri
to get the calling page that called my WEB API 2 Web Service.
I have a web application which fetches information from a web service. It works fine in our development environment.
Now I'm trying to get it to work in a customer's environment instead, where the web service is from a third party. The problem is that the first time the application tries to fetch information it cannot connect to the web service. When it tries again just seconds later it works fine. If I wait a couple of hours and try again, the problem occurs again.
I'm having a hard time believing this is a programming error, as our customer and the maker of the web service thinks. I think it has to do with one of the IIS or some security in the network. But I don't have much to go on and can't reproduce the error in our development environment.
Is it failing with timeOutException when you try to connect first time?. If yes, this could be the result on start up time of the service
I have a rule: "Always assume its your fault until you can demonstrate otherwise". After over 20 years, I still stick to it.
So there are therefore two cases:
The code is broken
There is a specific issue with the live environment
Since you want to demonstrate that the problem is (2) you need to test calls to the service, from the live environment, using something other than your application. Exactly what will depend on the nature of the web service but we've found SoapUI to be helpful.
The other thing that's not clear is whether you are making calls to the live service from your development environment - if, in testing, you're not communicating with the same instance of the service then that's an additional variable that will need to be considered (and I appreciate that you're not always given the option).
Lastly, #Krishna is right - there may be a spin up issue with the remote service (hence my question about whether you're talking to the same service from your dev environment) and -horrible as it is - the solution in the first instance may simply be to find a way to allow for this!
The error was the web service from the third party. The test stub we got to develop against was made in C# and returned only dummy answers. The web service in the customer environment actually connected to a COM object. The first communication with the COM object after a longer wait took almost a minute.
Good for me that the third party developers left the source code on the customer servers...
I am designing a error logging feature so our servers (each donig different things) can have a central data store for logging errors.
Would it be a good idea to have the various applications writing to the error log file using a WCF service, or is that a bad idea?
they can do it just by ADO.NET to the database, which I think is the simpler route.
How about having a look at syslog? It was made for exactly that purpose.
I'd say just log to your local data store. The advantages are :
Speed - it's pretty rapid to just
dump your chosen error report to an
existing data connection.
Tracability - What happens if you
have an error in your service? You
lose all ability to chase down
errors on all servers.
Simplicity - If you change the
endpoint for your errors service,
you have to update every other
application that uses the error
service.
Reporting - Do you really want to
trawl through error reports from
tens / hundreds of applications in
one place when you could easily find
them in the data store local to the
app?
Of course, any of these points could be viewed from the other side, these are just my opinions.
We're looking at a similar approach, except for audit logging as well as error handling.
Looking at using WCF over netTcp, also looking at using the event log, but that seems to require high trust settings, and maybe performance issues.
Not convinced by ZombieSheep's objections:
It's pretty rapid to dump your chosen error report over an existing WCF connection. Seriously. Plus, you can do it async/queued. Not a key factor for me.
You log to the central service and the local service. When the erroer service comes back on line, you poll your machines for events since the last timestamp. Problem solved.
Use a dns alias, and don't change the path - the way you should do internal addressing anyway IMO.
What if you have multiple apps on a single machine? What if you want to see the timing of errors across multiple apps?