Traffic not capture unless .NET Core SDK installed

[Stu]

We have a .NET Core 2.1 web application which is just run from the command line. E.g.

dotnet MyApp.dll --server.urls http://localhost:44321

The application communicates with other web services on localhost.

Fiddler tracing worked fine on our development machines, with all the traffic to the web services traced OK.

However, on the target machine, Fiddler did not tracing the web service traffic. It traced everything else. For example, traffic to/from our application, traffic to/from browsers.

The machine had .NET Core 2.1 installed with the "Runtime and hosting bundle" installer: https://dotnet.microsoft.com/download/dotnet-core/2.1

After trying various things (checking firewall, proxy, etc), we found the resolution was to install the SDK for .NET Core 2.1.

Does this imply that if we want to use Fiddler with .NET Core applications, we need to always have the SDK variant installed?

 

 

 

[Eric R | Senior Technical Support Engineer]

Hi Stu,

It should not be required to install .NET Core SDK to monitor traffic. There are a few different approaches that could help your scenario and I have listed these are below along with additional information.

Option 1: Configure Fiddler as a Reverse Proxy 

Option 2: Monitor Traffic on Remote Machine

 

Overall, it isn't clear if this has something to do with Fiddler or ASP.NET Core 2.1. Since this issue resolved itself after installing the SDK and this appears to be happening from a number of different causes, my guess is this is environmental.

For your reference, here is some additional information that I found. According to GitHub Issue #1962, it might be caused by the use of a lightweight web server instead of a full web server like, IIS. Additionally, it could be the change in the Default Provider in 2.1. 

I hope this helps. Please let me know if you have any additional questions. Thank you.

Regards,

Eric R
Progress Telerik

[Stu]

Thx Eric.  

We've now moved to use .NET Core 2.2, and also decided to go with a self-contained deployment of our application.  This is working, and we also do get Fiddler capturing as expected, so all is good now.

I am not sure if the original issue was Microsoft .NET Core and/or Fiddler related, however we are going to move forward with .NET Core 2.2 and deploy a self contained application.