how to restart asp.net application besides modifying web.config

Touching web.config from inside an application is a bad idea, IMO. Also, the idea of having a file that you modify is a little hackney, IMO.

The documentation specifically states that UnloadAppDomain will shut the application down:

UnloadAppDomain allows programmatic shutdown of unused applications.

You should be able to make this call anywhere in the application. Mind you, you might get a SecurityException, so make sure that the runtime gives you the appropriate permissions (you might want to put this in a library and make a call and then set the library up in the GAC with evidence to give it full trust).

this code work for me. just call it to reload application.

System.Web.HttpRuntime.UnloadAppDomain();

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This method will just unload our application. If you just put this method in an ASP.NET web button you are totally done. So when will our application reloaded? Actually if you click your button it will first launch our method and unload application. Further on the web page we are on at that moment will be reloaded as well, because we just clicked a button and the web page should refresh. After launching our method the page refresh process will cause our application to reload as well.

You can stop and start the Application Pool associated with the app as well.

You can do this by calling the HttpRuntime.ShutdownAppDomain method (you will need to use reflection to invoke it, since it is a private static method)

See How to restart an IIS Worker Process programmatically (i.e. shutdown the current ASP.NET Domain) for an example of how I use this method in a 'Restart' REST API

You could safely restart a web application by creating or renaming a folder at run time under the application directory. Obviously you need to give the user assigned to run the application "modify" rights to the web directory or to a sub directory under it.

the method is mentioned at http://www.bartlannoeye.be/blog/restarting-a-.net-web-application-without-restarting-iis

I used the following code to do it in my case. Modify it to work on a "writable" sub-directory

protected void RestartButton_Click(object sender, EventArgs e)
{
    //restart web app (instead of iisreset)
    DirectoryInfo dir = new DirectoryInfo(Server.MapPath("restart"));
    if (dir.Exists)
    {
        Directory.Move(dir.FullName, dir.FullName + "ed");
    }
    else
    {
        DirectoryInfo dired = new DirectoryInfo(Server.MapPath("restarted"));
        if (dired.Exists)
        {
            Directory.Move(dired.FullName, dir.FullName);
        }
        else
        {
            Directory.CreateDirectory(dir.FullName);
        }
    }
}

If you don't want to stop and start the app pool you can always recycle it.