How to measure impact of IIS rewrite definitions?

[AntonioSousa]

I have an IIS web application where there are hundreds of URL rewrite definitions in the Web.config file. It seems that each of the rules is being evaluated for each request, so it seems to me like at least a little of overhead.

I have been trying to figure it out in Dynatrace, but I'm a little limited because I'm experiencing this in an Azure web-app application. I don't see anything interesting in IIS Modules Insight, and have also tried the Method Hotspot approach, but with no relevant data.

Has anyone ever had an encounter with such a large number of rules, and measured it's impact in Dynatrace?

[skrystosik · Accepted solution]

You can't measure it in Dynatrace itself. Method hotspots are operating on .NET level, not IIS itself. In general best way to determine what possible overhead could be is by checking what is avg time between starting processing request on IIS side and .NET side of the application. This time delta is what you are looking for. If this application has issues with this time and you don't see anything in modules, this may be a root cause of overhead. If you see that requests came from IIS to .NET without any time loss, it's not affecting the application (which doesn't know that such a situation should exist for many reasons).

Sebastian 

[AntonioSousa · Accepted solution]

@skrystosikGood points! I was looking for that data in IIS modules, but since it's in a webapp, I don't get that information. I have also tried at the code level, but it also doesn't help. Have any idea on how to measure that time delta you refer to?

[skrystosik]

You should see it on PurePath Waterfall view

[AntonioSousa]

@skrystosik,

Looking at the Purepath waterfall, the only place where it might appear is in the code level. But it does not; I believe it happens in IIS before it is passed to the application level, which is what Dynatrace sees.

[skrystosik]

Yes, but I mean that you will have delay between IIS and .NET, may be visible as client side error. This may be this time. I don't have for now resolution for that. Perhaps some custom development using OneAgent SDK may be needed.