Traffic not capture unless .NET Core SDK installed

3 posts, 0 answers
  1. Stu
    Stu avatar
    2 posts
    Member since:
    Jul 2019

    Posted 03 Jul 2019 Link to this post

    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:

    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?




  2. Eric R | Senior Technical Support Engineer
    Eric R | Senior Technical Support Engineer avatar
    388 posts

    Posted 09 Jul 2019 Link to this post

    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.


    Eric R
    Progress Telerik
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  3. Stu
    Stu avatar
    2 posts
    Member since:
    Jul 2019

    Posted 15 Jul 2019 in reply to Eric R | Senior Technical Support Engineer Link to this post

    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.

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