2012R2, IIS, and KB3052480 - random ASP.NET app domain restarts

I will leave out the 'how we came to this conclusion' part, but suffice to say it took 3 people the better part of 2 full days.

There is a, in my humble opinion, rather gaping bug in 2012R2 IIS that manifests itself like this:

  • You have many file changes in the web root, but they are contained to the 'safe' directories (i.e. not in /bin or whatnot)
  • In theory, IIS doesn't care and you go about your merry way - because it only monitors /bin and /app_data (iirc?) and some config files
  • You find yourself chasing spikes in your (New Relic) data, traces that make no sense (the transactions that get called the most have a lot of looong traces)
  • Nobody understands what's going on, because no errors are being thrown
You can verify that you're seeing a lot of ASP.NET app domain restarts by looking at perfmon:
ASP.NET Applications - (your instance) - Application Lifetime Events

What you should be seeing upon a legit recycle is one startup event and one shutdown event, and possibly a 'compilation started' event.

What happened in our case is that (we suspect) Launch Darkly log files were being written to a lot (which is fine), but IIS was detecting these as configuration changes.  We found that by adding a <healthMonitoring> rule in: C:\Windows\Microsoft.NET\Framework64\Config\web.config

<add name="Application Lifetime Events Default" 
 eventName="Application Lifetime Events" 
 custom="" />

Do an iisreset and you'll see log start to come into the application event log.

EventID: 1309
Source: ASP.NET 4.0.30319.0
Event code: 1002
Event messsage: Application is shutting down. Reason: Configuration has changed.
Event detail code: 50004

A lot of googling/digging later, we turned up this hotfix: https://support.microsoft.com/en-us/kb/3052480

After applying the hotfixes and rebooting the servers (yes, it prompts you to restart even though the documentation states otherwise), we have seen ZERO app domain restarts.


Unexpected ASP.Net application shutdown after many App_Data file changes occur on a server that is running Windows Server 2012 R2

Consider the following scenario:
  • You have a server that is running Windows Server 2012 R2.
  • You set up a website on Internet Information Services (IIS).
  • You create a simple website that creates or deletes lots of files in the App_Data folder.

In this scenario, you experience an unexpected ASP.NET application shutdown because of high disk I/O and configuration changes.


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