Scott Hanselman

Exploring your .NET applications with dotnet-monitor

September 24, 2020 Comment on this post [6] Posted in
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I talked about Cross-platform diagnostic tools for .NET Core and dotnet-trace for .NET Core tracing but I would be remiss if I didn't show and mention "dotnet monitor."

dotnet monitor is an experimental tool that makes it easier to get access to diagnostics information in a dotnet process. If you're running .NET Core within a container - or mostly likely in Kubernetes - this tool offers an insight into your running microservice. Basically it creates a microservice of its own that you can interrogate to better understand what's happening.

HELP! Confused about Kubernetes? Check out http://computerstufftheydidntteachyou.com and my most recent video on Kubernetes and Container Orchestration.

Assuming you have .NET Core installed, you can install dotnet monitor as a global tool:

dotnet tool install -g dotnet-monitor --add-source https://dnceng.pkgs.visualstudio.com/public/_packaging/dotnet5-transport/nuget/v3/index.json --version 5.0.0-preview.*

You then just run it along side your project or running process.

dotnet monitor collect

The developer blog on dotnet monitor shows you how you can share a volume mount between your application container and a container running dotnet monitor if you like. If you're in k8s (Kubernetes) you should run dotnet monitor as a sidecar to your container within the same pod.

It'll start up and you can talk to dotnet monitor with curl, wget, and pipe through jq and hit localhost:52323/processes to get a list of .NET Core processes it can think about.

NOTE: If you are running this locally and get auto redirected to HTTPS then you may have a cached HSTS policy for localhost from other work. Head over to edge://net-internals/#hsts (or chrome://) and scroll to the bottom and delete the Domain Security Policies for localhost.

Now I can curl and see the output. I have my podcast on the left pane in Windows Terminal, dotnet monitor collect in the upper right, and the output lower right.

dotnet monitor

Once I figure out my process id (PID) - which will be automatic within a container as there will only be one - I can explore any of these local endpoints:

  • /processes
  • /dump/{pid?}
  • /gcdump/{pid?}
  • /trace/{pid?}
  • /logs/{pid?}
  • /metrics

If you are getting the logs, you'll get a never ending text/event-stream in your browser. I'd recommend you "curl" to see this at the command line.

text/eventstream in your browser

You can also get momentary traces, collect a nettrace file and analyze it in Visual Studio, PerfView or other tools.

The dotnet monitor is experimental, but if you're digging it, head over to the dotnet/diagnostics GitHub and show some support.

SOS and Other Diagnostic Tools

  • SOS - About the SOS debugger extension.
  • dotnet-dump - Dump collection and analysis utility.
  • dotnet-gcdump - Heap analysis tool that collects gcdumps of live .NET processes.
  • dotnet-trace - Enable the collection of events for a running .NET Core Application to a local trace file.
  • dotnet-counters - Monitor performance counters of a .NET Core application in real time.

Hope this helps you!


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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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October 02, 2020 7:51
Thank you Scott.
October 02, 2020 10:13
Thank you sir for sharing this post
October 05, 2020 12:48
Really useful tool. I've run this for my project, it worked like a charm.
October 05, 2020 15:24
Any recommendations for non-Core .NET monitors?
October 21, 2020 6:53
i love such content. thanks.
October 24, 2020 16:51
Hi there! Would you mind if I share your blog with my twitter group? There's a lot of people that I think would really appreciate your content. Please let me know. Cheers

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Disclaimer: The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.