If my ASP.NET webapp isn't fit for runtime?

I want to run some tests when my ASP.NET webapp comes online (preferably before anyone tries to access it), to make sure all of my runtime dependencies are available as I expect them to be.

When is a good time to perform these tests (e.g. Application_Start, Application_Init, somewhere else, etc开发者_C百科), and what's a good technique for making my webapp unavailable to users if my tests fail (it shares an app pool with other apps I don't want to affect)?

One approach would be to put your checks in the Application_Start event, and update a static property (or properties) in the Global class with the result of your test.

If you're using master pages, each master page (I've personally never seen more than 2 base master classes in a project) could check the static property in the Global class, and redirect to an "app offline" page if appropriate. Since the static property would only be updated when the application started, there shouldn't be any performance impact.

The code in your master page's OnLoad event might look like this...

if (!Global.WasDependencyCheckSuccessful)
{
//redirect to error page
}

If you're not using master pages, this may not be the best solution (because you would need to update each web form in your site individually).

You can put it in the Application_Start event in the global.asax.

To bring your app offline, simply create an App_Offline.htm file. I do it on our server by having an "App_Offline.html" file and when I need to bring it offline, I have the code rename it to change the extension from .html to .htm, and reverse that to bring it back online.

Of course, to bring it back online, you have to do it from code outside of your website, or do it manually, because if the file is there, the code in your website won't run...