How to use a .NET 4.0 web application within a .NET 3.5 web application?

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Problem :

My company has a website built in ASP.NET and targets .NET 3.5. It is too mangled and massive to be converted to .NET 4 in a timely manner. I am tasked with building a ticketing system. I want this ticketing system to be a completely separate application from the main application.

I added a directory to the website called “TicketingSystem”, then in IIS I set this folder as an application, using an app pool that targets .net 4.0. I assumed this application would not be affected by the application above it, especially since it uses its own app pool, but it would seem it is being affected somehow. Navigating to this directory with my .net 4 web app in it generates this error:

I covered the sensitive information like file paths and stuff, but the line that says config file has a path to the parent application’s config file, not the config file of the .net 4 app.
Is it not possible to nest a .net 4.0 app within a .net 3.5 app?


As requested here is a screenshot of the IIS directory structure.

Solution :

Web.config inheritance is unfortunately not something you can turn off completely; Specifically, the top section in the web.config that defines which config sections exist in the web.config cannot be ignored/overridden inside a child application.

The solution is documented here( 4 breaking changes documentation); Essentially you have to move the values that are currently in the top application up into a machine/FrameworkVersion specific config file and then wrap all(or at least, most) of your root web.config in a location tag with inheritence disabled.

Have you tried setting the “inheritInChildApplications” attribute to “false” in the parent folder’s web.config file?

See Saul Dolgin’s answer to a similar question for how to do this.

In my applications I more or less succeed with nested applications by using the <location> element together with <clear /> and similar elements in the web.config.

This is an excerpt from a web.config file of mine:

<!-- Do not inherit. -->
<location path="." inheritInChildApplications="false">

The idea is to put all sections that you do not want to inherit to child applications within those location elements, as in my example above.

Assuming that your current site uses AppPool1 targeted to .NET 2.0

Create AppPool2, target it to .NET 4.0 and use it by virtual dir of your app.

Make sure that stuff isn’t in the machine config for the app pool. If so, just delete it from your web config.

As mentioned first port of call is to make sure each application has it’s own application pool. Double and triple check this as a .net 3.5 site and a .net 4 site in the same app pool will cause the entire app pool to break.

Next, try remove the entire scripting section group, from my experience it solves it and i’ve not noticed any problems

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