We have deployed a simple ServiceStack application delivering Podcast RSS-feeds in IIS 7. Scouring the IIS logs, we found that a tiny amount of the requests get a HTTP 500.19 error code.
Of the ~550 000 daily requests, around 600 of them fail with 500.19. Which means we successfully deliver RSS on 99.9% of the requests. I am still curious to understand why we fail for 0.1% of them.
500.19 generally happens due to an invalid configuration. How can the config fail for only 0.1% of the requests?
I have not been able to reproduce the error manually, so I don't have the HResult code. This is not present in the IIS log either. However, the sc-win32-status in the IIS log is 64
- The internal logging of the application never reports any error, suggesting the request never reaches our code.
- The error usually happens to the biggest RSS (740KB gzipped), but also happens to smaller ones (140KB gzipped).
- The failing requests usually comes from mobile clients (IOS, Android), which doesn't tell much as podcast is usually consumed on mobile.
- The application is deployed on 6 nodes, load balanced with BigIP. Config file is not shared accross nodes. The 0.1% error rate is equal on all nodes.
- We have output cache activated in IIS (but no kernel cache).