Failing Ping tests on Application Insights

Whilst setting up Application Insights on one of our web sites I hit a problem. The target site appeared to be working OK, but if I setup a ping test it failed.

Digging into the failure, as with much of Application Insights just keep clicking to go deeper, I found the issue was that a CSS file was failing to load.

Presumably on this Umbraco site the CSS file is meant to be loaded for the site but none of the styles are actually used, hence the site renders OK.

The fix was to make sure the video.css file was present on the server. So Application Insights found a problem with a production system – just as it is meant to!

So it is important to remember that the ping test is not the simple thing I thought it was, it is actually a full page load, making sure that only 200 OK responses are seen.