IIS 8.5 on Server 2012 R2 stops responding after a time

I recently updated a server from 2008 R2 to 2012 R2 that hosts a few MVC sites and a Web API. After deployment, everything seems to work fine for a few days before the web API seems to fail. It returns a 404 for all requests to the API from the failure forward. The parent MVC site seems to continue working fine.

A few things:

• The web API is hosted as a web application inside a parent website within IIS.
• This is a 4.6.2 framework site and API.
• I would prefer it to be its own site but I don't control this.
• It seems to stop at roughly the same time when it occurs - around 2:35 AM
• The only route defined by the web API is a GET

I've checked the event log as well as IIS logs. The event log doesn't reflect anything during these times and the IIS logs just show a 404 response. Resetting IIS/AppPools/etc... don't fix the API nor does restarting the machine. In fact, the only thing that seems to fix it temporarily is a VS publish over top of site.

I suspect something to do with MSDeploy but have nothing concrete. Does anyone have any ideas on where to look or what to look for? I feel it must be something to do with the server configuration as we've never seen this problem prior.

I ended up finding out the problem. Our project uses NLog with the config specified to create a new log file daily. Something within either NLog or IIS recently decided not to play nicely together. A temporary fix was to turn off the daily file creation from within NLog. Since making this change, the site has stayed up consistently for the past week.

This post is what got me checking into NLog as a possible culprit.