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Help! My Application Insights telemetry stopped working.

I want to start this blog post by stating that I have a new hero and his name is Stijn. Let me explain why…

I recently upgraded an older .NET Full Framework application to the latest Application Insights NuGet package. This to make the switch from the obsolete instrumentationkey to the newer connectionstring approach.

After upgrading our packages.config file (yes, this project is so old) looked like this:

Looking good right? Unfortunately, the same could not be said about our telemetry itself as our Application Insights logs remained awfully empty.

I doublechecked all the config files, reinstalled the nuget packages, tried to explicitly force to flush the telemetry data, everything I could think of I tried. But nothing worked.

I handed the problem over to another team member (Stijn, my new hero) and he found the solution. After debugging the Application Insights code he arrived at a no-op method:

This method should have all the logic to read the configuration information and configure Application Insights for this ASP.NET MVC application. But as the method is empty, nothing is happening.

The root cause

After upgrading, the NuGet package manager silently switched from the .NET Framework 4.6 version to the .NET Standard version of Application Insights. Here's the problem: the .NET Standard version doesn't read configuration from your app.config or web.config files and provides only a void (no-op) implementation.

This means our application was running with Application Insights "installed" but completely non-functional—no telemetry, no logging, nothing.

The solution

To solve the problem, we changed the hintpath in the csproj that originally pointed to the .NET Standard version:

And updated it to the .NET46 version:

That fixed the problem. Great!

Thank you Stijn! I would never have found this one…

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