My Azure .Net web app uses a shared cache role which can sometimes throw an exception meaning, "retry later" if it is hot swapping. Currently, that causes my web app to error. However, this is thrown before my app has even started up since it is the framework/IIS which has attempted to setup the cache and failed.
How can I catch these exceptions and do something useful when redirecting to an error page would still require my app and config/cache to load, which would cause the exceptions again? Even if I could catch the exception in Application_Error, I don't think I can retry the connection to the cache because I didn't create it in the first place.
Few questions :
Didn't clearly get your question. So it's your client calling cache, who is getting these errors right?
Are you using session state provider for cache? If not, When you said you are not making connections to the cache, what did you mean?
What is the exact error?
Is it intermittent? Is it always happening during role startup, the case u mentioned here?
Related
Does it cause all the threads,I mean all the users to stop and increase the wait time http request queue and start to affect the availability of the application ?
If so should we make sure there is no exception left over in an asp.net application to ensure scalability of the application.
Some unhandled exceptions can terminate w3wp.exe. Therefore, you should handle exceptions. Application_Error can't handle which are thrown on another thread (background workers, fire and forget taks). You should use http module for these kind of errors. But it also can't catch stackoverflow erros. You should use some decarations for this, if you want handle exceptions on Application level. Here is more detail.
Other than this I think exceptions will not effect the other users. Exception and performance.
Basically, exceptions shouldn't happen often unless you've got
significant correctness issues, and if you've got significant
correctness issues then performance isn't the biggest problem you
face.
I liked this sentence :)
Does it cause all the threads,I mean all the users to stop and
increase the wait time http request queue and start to affect the
availability of the application
It depends on the exception. For example, OutOfMemoryException will affect all users.
On the other hands, FileNotFoundException wouldn't affect other user.
If so should we make sure there is no exception left over in an
asp.net application to ensure scalability of the application.
Well, we all developers try to write bug free code, but sometimes things slip out of our hand. It is why we use logging to catch run-time exceptions - such as Log4Net, NLog.
I have an MVC+SignalR application that has a lot of Reactive Extensions subscriptions flying around, all of which are projections of data coming from a Socket in realtime. Some of these subscriptions are not working as expected, and when they raise an exception it just goes into the void unless I'm debugging.
I had hoped that I could use Elmah to automatically log these unhandled exceptions, but it seems that unless the exception occurs on the same thread that's processing the request/response, eg it causes a yellow screen of death, Elmah isn't touching it. So my question is twofold:
Can I get Elmah to automatically log exceptions on background/worker processes?
If the answer to #1 is "no", what's my next best option, other than wrapping my subscriptions in try/catch blocks at a very high level?
Ad 1) If it doesn't happen already it probably doesn't.
I don't know how exactly you use background threads, but I will try to explain were ELMAH handling is working. ELMAH is integrated into ASP.NET pipeline, and when the error occurs it is handled by ASP.NET pipeline, which shows error page (like http error 500) and invoke ErrorLogModule. Moreover quoting Using HTTP Modules and Handlers to Create Pluggable ASP.NET Components -> Adding ELMAH to an ASP.NET Web Application
The section adds the ErrorLogModule HTTP module to the
ASP.NET HTTP pipeline. Make sure you include this
setting, otherwise ELMAH won't be listening for the Error event, and
therefore won't be logging any unhandled exceptions.
Ad 2) Because you are using Reactive Extensions you can handle onError in which you can automatically log into Elmah. If you don't want to writer everywhere error hangling in OnError, just create your own function or method extension which will wrap it automatically for you. Writing into ELMAH manually is simple just call:
Elmah.ErrorSignal.FromCurrentContext().Raise(ex);
I have an ASP.NET-based web app on Azure with a Web API. Yesterday, I started to get exceptions from the app whenever one of the API calls was invoked.
I don't have an exception logger intercepting application exceptions at the moment, however, I do have audit logging on each of the API calls which 99% of the time catches exceptions and reports problems to me.
In this particular case, it appears an exception is occurring further up the stack from the audit logging. There's not much code I have written which is invoked above there to be honest. There is also an IIS error page configured, so exception information is not passed down to the client. I have had a look in the event log and there's nothing in there.
In reaction to the problem, I spun up a new Azure instance, made that live and relegated the problematic instance to staging. The new instance works fine. If I restart the (now) staging instance by reconfiguring web.config to disable IIS errors then that instance will also work fine!
So does anyone know how I can extract unhandled exception information from a running app domain without having to restart it or affect it in any way?
I will be putting exception logging in soon, don't worry :-) But if there is a way to crack this without having to wait for another occurrence of the problem then that would be great!
UPDATE:
I logged onto the server and managed to get the following information from the "detailed response":
HTTP Error 500.0 - Internal Server Error The page cannot be displayed
because an internal server error has occurred. Detailed Error
Information:
Module ManagedPipelineHandler
Notification ExecuteRequestHandler
Handler System.Web.Http.WebHost.HttpControllerHandler
Error Code 0x00000000
Requested URL http:// 10.77.52.122:80/api/Login
Physical Path E:\sitesroot\0\api\Login
Logon Method Anonymous
Logon User Anonymous
Request Tracing Directory
C:\Resources\directory\34c6b40352d4449d8a19274caa328300.Web.UI.DiagnosticStore\FailedReqLogFiles\Web
I then configured Failed Request Tracing - which promptly made the error go away!
Anyone have any ideas? I'm probably going to have to wait for it to happen again, but by then there'll be some more exception logging.
thanks
Kris
... will the Application_Start method be ran again for the next request(s) or not?
Does it depend on ASP.NET version, hosting server version and/or other context?
I am trying to determine if it's a good thing to load critical assemblies there or not. For example data access assemblies which are vital to the functioning of the whole application or not. Failure to load such assembly would make subsequent requests useless.
Application_Start will be fired only once for each web application so in your case, the start will not happen again for subsequent requests.
Typically, I prefer to put one time start-up code in the application start within try-catch and if there is an exception then set the global error flag. In each BeginRequest, the flag is checked and if it is set, user is redirected to a custom error page indicating the site is down and please contact the administrator.
I have an ASP.NET C# 3.5 web application that consumes another ASP.NET web service as a web reference. The web service is built into some proprietary hardware device. The problem is that that device has been having troubles and not alwasy accessible. My web application is suffering brcause of it, as it takes over a minute to load. It does load, but not acceptable.
The service is instantiated in a try catch block and no exception is being throw, but the output windows displays:
A first chance exception of type 'System.Net.WebException' occurred in System.dll
I know there is a better way to handle this, but I am drawing blanks.
Any help is appreciated.
UPDATE: Still looking for an answer on how to handle webservices that become unavailable without affecting website.
After tearing it apart, I found the exception. It is a standard "Unable to connect" exception. The problem is now the timeout, I have tried setting the asyncTimeout to 5000 in the web.config under the System.Web -> Pages properties. It is still taking aroung 20 seconds to throw the exception. Any ideas?
If you saw a "first chance exception" but your exception handler didn't get it, that means that the exception was handled elsewhere (swallowed, consumed by an exception handler, etc.) Perhaps something in the .NET libraries already handled that exception, and you need not concern yourself with it in your code. Or maybe you left some exception swallowing somewhere in your code.
You ought to consider using a timeout in your web request.
Simple solution, poll the service using JavaScript after page load.
Without any details regarding frequency/usage of the service and not seeing any code, heres a thought or two.
Its most likely the web method on this hardware that giving the error, so I'd pursue any support options you have (if any), but just for giggles, try this first to see if it helps....
I noticed that some people online said that they were able to get around this (in their scenario) by setting the KeepAlive to false on the requesting object, so that way your aren't inadvertently using an old (stale) connection to the service. You may be trying to "Keep Alive" but the webserver timed out the connection on you. Worth a quick try...
Good Luck!
In addition to the above, I would use a http debugger (like fiddler2) to get a better idea of what is happening on the wire.