Some web applications need to load large amounts of data, or perform expensive initialization processing, before they are ready to process requests.  Developers using ASP.NET today often do this work using the “Application_Start” event handler within the Global.asax file of an application (which fires the first time a request executes).  They then either devise custom scripts to send fake requests to the application to periodically “wake it up” and execute this code before a customer hits it, or simply cause the unfortunate first customer that accesses the application to wait while this logic finishes before processing the request (which can lead to a long delay for them).

ASP.NET 4 ships with a new feature called “auto-start” that better addresses this scenario, and is available when ASP.NET 4 runs on IIS 7.5 (which ships with Windows 7 and Windows Server 2008 R2).  The auto-start feature provides a controlled approach for starting up an application worker process, initializing an ASP.NET application, and then accepting HTTP requests.