<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <system.web>
        <httpRuntime waitChangeNotification="300" maxWaitChangeNotification="300"/>
    </system.web>
    <system.webServer>
        <modules runAllManagedModulesForAllRequests="true" />
    </system.webServer>
</configuration>

But there’s one more catch.

ASP.NET will unload the application as
soon as the web.config is changed,but
it won’t actually reload it and apply
the “waitChange…” settings until a
request is made. So you could still
drop the app_offline.htm and
web.config in,and if the first requst
occurs while a dll is only half
copied,the exception will occur. To
add insult to injury,the exception
will persist until you replace the
temporary web.config or the total
duration of your “waitChange…” time
expires!

To get around this final hurdle,you’d
need to make a request to the
application after uploading the
temporary web.config,but before you
start deploying the application files.
The complete process is as follows:

1. Add app_offline.htm
2. Replace application’s web.config with a temporary web.config (as above)
3. Request any ASP.NET resource on the site so the new
   waitChangeNotification gets “applied”*
4. Make any file system changes necessary (deploy bin dlls,other site
   files)
5. Replace temporary web.config with the original application
   web.config
6. Delete app_offline.htm

*You may dispute what happens in step 2-3,since ASP.NET shuts down the
application after step 1. Indeed,it
does not appear from my event viewer
that the web.config change is
registered or “applied” as a result of
either step 2 or 3,but nevertheless
the updated waitChangeNotification
settings do get applied after step 3.

More app_offline.htm woes

App_offline.htm gotchas with ASP.NET MVC