IIS 7 and Above
Application Request Routing (ARR)
Any way to log ARR_SERVER_ROUTED Server in ASP.NET
Re: Any way to log ARR_SERVER_ROUTED Server in ASP.NET
Jun 01, 2018 11:46 PM|Rovastar|LINK
I don't know about writing your own modules (and to be honest I doubt you will get much help to this here for module writing) but often you can work out what is happening and why you are getting your 502.3's
The server the request is going to is in the IIS logs.
502.3 errors are common on ARR. They occur when the request doesn't come back (or there are no available servers). Requests that take too long timeout can be a cause.
Really you should be able to work put what is happening from the backend server. You know the URL and timestamp and the backend server on the ARR. Then you can look to see what happened on there. The request in your case looks like it was routed through.
Maybe look at how long the request took on the backend and align that with your proxy timing on the ARR for that farm.