How to Determine ASP.NET Application Domain Lifetime

Question

We have an application gathering counter statistics and we would like the values to reset after executing the iisreset command and that's all.

Microsoft says Application_Start is:

Called when the first resource (such as a page) in an ASP.NET application is requested. The Application_Start method is called only one time during the life cycle of an application. You can use this method to perform startup tasks such as loading data into the cache and initializing static values.

This is how we're currently doing it:

protected void Application_Start(object sender, EventArgs e)
{
    _counters.Get<AutoCounter>("TAS:RequestCount").Reset();
    _counters.Get<AutoCounter>("TAS:RequestTime").Reset();
    _counters.Get<AutoCounter>("TAS:TimeBetweenErrors").Reset();
    _counters.Get<AutoCounter>("TAS:ErrorCount").Reset();
}

However, these are resetting at unexpected intervals. What determines when the application domain's life-cycle ends and this method is called on the next request?

Answer 1

There are a lot of reasons why a Web app gets restarted. This article includes the following partial list.

• the web.config is edited

• the machine.config is edited

• the global.asax is edited

• files are changed in the bin
  directory of the web app, or one of
  the bin's subdirectories

• a directory is created, renamed, or
  deleted within a web app directory

• an ASP.NET file (aspx, asmx, etc.) is edited (and therefore recompiled)
  more than 20 times, a default set in the machine config as an element
  named numRecompilesBeforeApprestart

• by way of settings of various
  attributes in the
  element in the machine.config, which affect the restart/shutdown of the
  worker process itself. On Windows
  2003, when not using IIS5 isolation
  mode (which is not used by default), these elements are
  ignored and instead the settings in
  Application Pools in IIS manager are used

My guess is that your approach is good but now what you really want to know is what's causing the restart and if you should be alarmed.

Answer 2

In IIS 6.0, the application pool performance tab allows you to shutdown the IIS worker process after a specified idle time. This is enabled by default and is set to twenty minutes.

This could be the cause of unexpected application_start events being triggered.