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A way to have different LogPaths for elmah, based on error types

I am looking for a way to have different log path for different error types in my web api project. What I want is to put System.Web.HttpException errors in different folder and my other errors in a another folder. The reason for that is, I receive so many System.Web.HttpException errors which most of them are irrelevant but I still need to log them but in a different folder. My elmah setup is a standard one.
this is my web config tag:
<errorLog type="Elmah.XmlFileErrorLog, Elmah" logPath="~/App_Data/ErrorLog" />
<security allowRemoteAccess="false" />
</elmah>
any help is much appreciated.

The short answer: You can't. XmlFileErrorLog only supports a single directory as logPath.
If you want to implement this, you would need to fork the ELMAH source code and override the Log-method of XmlFileErrorLog.
Another approach could be to use ELMAH error filtering to ignore all System.Web.HttpException errors and then use another logging framework to log those errors. If you set up log4net, NLog, Serilog or similar, you could make that integration log all errors (including the HTTP exceptions).

In asp.NET using C# can I create an error log?

I have a C#.net site which displays custom error pages to the user. This is set in web.config:
<customErrors mode="Off">
<error statusCode="500" redirect="~/error.cshtml" />
<error statusCode="404" redirect="~/error.cshtml" />
</customErrors>
The problem is that if there is an error, I have no record of what it was. I'm familiar with PHP where I can set a location for the error_log file which I can then check for PHP errors. Is there a way to do something similar in .NET?

You can use log4net dll, it has provisions to log errors as well as diagnostic messages.
Link where the log4net is available :
https://logging.apache.org/log4net/release/example-apps.html
Codeproject demo to get started :
http://www.codeproject.com/Articles/8245/A-Brief-Introduction-to-the-log-net-logging-librar

You can try NLog. Here is a Tutorial

You can use the built-in logging functionality that comes with ASP.NET.
Set it up in system.diagnostics in web.config, declare a trace source in your code and off you go.
You can configure it to write to the event log as well as log files and custom destinations.
I just did a quick google search and found an introductory article here: http://www.thejoyofcode.com/from_zero_to_logging_with_system_diagnostics_in_15_minutes.aspx
You will find many more without too much effort.

Have a look at the HealthMonitoring possibilities that come with ASP.Net. For instance, you can get references to exceptions and send emails with the exception to a specified address. A couple of years ago I wrote this article about HealthMonitoring: http://www.tomot.de/en-us/article/6/asp.net/how-to-create-a-custom-healthmonitoring-provider-that-sends-e-mails
If you want a more mature error logging solution, have a look at Elmah.

Is there a way in Visual Studio to configure the default start page for web deployment starting from Empty ASP.NET Web App?

Entry level web developer here, thank you in advance.
A very basic single page website starting from Empty ASP.NET Web Application adding each and folder file from scratch. Everything works fine locally bare bones. I'm trying to configure the start page in the subfolder "html" to the file index.html. I get the default "This website has been successfully created" after publishing. Azure web service is working fine because I can go to site.azurewebsites.net/html/index.html to see my page after it's published.
Right clicking the project and going to properties to set as start page, or going to Properties>Specific Page doesn't work as suggested here for deployment but works fine locally. Altering the web.config file as suggested here gives me an internal server error that is fixed once I remove the code
<system.webServer>
<defaultDocument enabled="true">
<files>
<clear />
<add value="html/index.html"/>
</files>
</defaultDocument>
</system.webServer>
I tried different variations of this all with the same internal server error. Is my syntax correct?
I then created a global.asax file and changed the Application_Start line as suggested here:
protected void Application_Start(object sender, EventArgs e)
{
Response.Redirect("/HTML/index.html");
}
Same result.
Lastly, I created an App_Code folder with a RedirectHandler.cs file as suggested by Rion Williams's last suggestion (first link) along with his code and sure enough I get the same result.
"This web app has been successfully created" after publish but I see my desired start page after adding /html/index.html to the end of the url.
Understanding how basic this problem is I took extra care to exhaust as many google searches as I could find relating to the topic before asking this question. My first question on StackO so my reputation is too low to link each page I found. My next attempt is to just start a brand new MVC project and painstakingly rearrange every single file that way. I'm confident that will work but I didn't want to leave this simpler method without learning from what I did wrong especially when I know the answer is going to derp-slap me in the face.

Have you tried to configure the default document under the configuration tab for your website in Azure portal?

With a lot of changing file locations around, clearing cache, and rebooting to avoid server and runtime errors, #hernandgr had the simple option I hadn't known about (shame on me) and funny enough couldn't successfully google about.
It turns out that I didn't need to do any of the steps I had tried to configure the start page beyond just changing it in the configuration tab in the Azure Management Portal. I deleted the global.asax file and the App_Code folder completely, didn't need to touch the web.config in any way and didn't need to implement MVC.
One thing to be noted was that making index.html my start page through Azure seemed to push it up a directory so my CSS, JS, LESS, fonts, and images folders had to be moved up as well to display the page properly.

Discovered WCF service can't connect

I have a WCF service that I'm using to expose a data source (connected to via an EF model). My endpoint for some reason just stopped responding.
Up until my last changes I was just pulling the data at startup of my app. I'm now working on adding a subscribe/publish model on top of this so I can throw events when something hits the WCF service that results in the data changing (could do it in the client side but than I wouldn't catch other users changes).
I've been following the example from Microsoft: http://msdn.microsoft.com/en-us/library/ms752254.aspx and added the appropriate decorations to my service interface and implementations and added a subscribe/unsubscribe OperationContract etc. I than try to fire up the service and can't connect.
I than dropped the Service Reference from my client and tried to reattach. Here is the strange thing:
1) The WCF service builds and spins up in the developer host.
2) The Web.Config file wasn't touched.
3) The "Discover Services" option in the add service reference in vs 2012 sees the service but when I try to actually accept the discovered service it throws an error saying "error downloading metadata from the address.
I don't get how it can discover the service and then not be able to add it as a reference. I can see if I added the info myself but it found it.
As part of adding the publishing functionality I added the SessionMode.Required tag to the interface I'm not really sure how WCF handles sessions and haven't ever had to deal with sessions anywhere else in my coding (generally pull the data from the source and than process it locally has been the types of tools I needed to make in the past so no state needed to be persisted server side).
Any ideas?
my service web.config:
<connectionStrings>
<add name="TaskModelContainer" connectionString="metadata=res://*/TaskModel.csdl|res://*/TaskModel.ssdl|res://*/TaskModel.msl;provider=System.Data.SqlClient;provider
connection string="data source=winhacker\sqlexpress;initial
catalog=TaskDB;integrated
security=True;MultipleActiveResultSets=True;App=EntityFramework""
providerName="System.Data.EntityClient"/>
Note: Note sure what is going on with the formating most of the file doesn't show up in the preview but sufficience it to say it is the boilerplate one that gets autogenerated other than I added a connectionStrings section to like to my EF datapoint. If you want to see the file click on "edit" seems to show the source I copied though a bit formatted weird.

In the vast majority of cases where I have encountered this error, the issue has been a serialization issue on the server side; WCF will throw an exception about this during the metadata discovery phase, but VS does not display this exception.
In order to troubleshoot this problem, you need to add a diagnostics section to your web.config to capture the WCF information into a svclog file, then use Microsoft's Service Trace Viewer to examine the log and discover the actual exception being thrown.
The web.config section should look something like this:
<system.diagnostics>
<sources>
<source name="System.ServiceModel"
switchValue="Information, ActivityTracing"
propagateActivity="true">
<listeners>
<add name="traceListener"
type="System.Diagnostics.XmlWriterTraceListener"
initializeData="c:\log\WebTrace.svclog" />
</listeners>
</source>
</sources>
</system.diagnostics>
and be added at the <configuration> level.
Once you have added the configuration and ensure that the specified directory exists, try adding the service reference again. This should cause the specified svclog file to be generated.
If you have VS installed on that machine, you should be able to just double-click the file in Windows Explorer and have the log opened automatically in the tool.
Once the log is opened, look down the list of activities in the left hand pane and click on the first one in red. Then, in the top right pane, select the first one that is red (or shows an exception, I forget which). You can then click on that to see the details, including exception information in the bottom right pane.

global.asax not being updated

We have a web application where we are using global.asax for url rewriting. We use a compiled version of the site on the live server.
As a part of modification request, we had to add some custom native AJAX code where javascript would call a webservice to update the content of the page. For being able to call the webservice with extension .asmx, we modified the url rewriting code to handle asmx requests seperately.
this arrangement works fine on the local machine, but when we publish the site and deploy it on the live server, the new code doesnt seem to get included. It still skips the condition to check the ".asmx" extension, and throws a page not found exception considering the webservice name as a page name.
We have tried looking all over and googled for such things as well.. but no avail..
any pointers on what might be going wrong.. ?

Assuming your URL rewriting is good (isn't that normally implemented as a HttpModule?) I'd check to make sure that there's an ISAPI mapping in IIS on production that sends .asmx requests to ASP.NET.
If you think your changes to the global.asax haven't been rejitted then you can always stop the application pool, go find your web applications compiled bits in c:\windows\microsoft.net\framework[version]\temporary asp.net files... and delete the jitted version. I've seen ASP.NET miss when it comes to Jitting changes before.
I'd also consider running http fiddler (IE) or tamper data (FireFox extension) on one of the pages that makes calls to the web service. It will tell you exactly how the page is calling the web service and you can validate that the called URL is correct.

There is machine.config file where you can add HttpModules. I also think that you can do that through web.config.

One reason I can think of is that in the Web.config, you might have configured the routing module in the system.web section but not in system.webServer (or at least forgot something in there).
I the similar problem before and the solution was to remove the module & add it again in the system.webServer section of the Web.config like this:
<system.webServer>
<modules>
<remove name="UrlRoutingModule" />
<add name="UrlRoutingModule" type="System.Web.Routing.UrlRoutingModule, e="RoleManager" type="System.Web.Security.RoleManagerModule"/>
</modules>
</system.webServer>
It might be a different module or handler but the idea is basically the same. It's important to "remove" the module first.