App service https 4xx errors not showing in application insights

Hi @gaurav sharma
Thanks for the question and using MS Q&A platform.
Based on the monitoring data you've shared I understand you're experiencing an issue where Application Insights isn't showing performance data despite having both App Service diagnostics and Application Insights connected to the same Log Analytics workspace.

You're correct - Application Insights primarily requires instrumentation from within your application code to collect detailed performance telemetry. Simply connecting App Service diagnostics to Log Analytics workspace is not sufficient for Application Insights to show performance data.

Instrument your application code with Application Insights:

For .NET applications:

<!-- Add to .csproj -->
<PackageReference Include="Microsoft.ApplicationInsights.AspNetCore" Version="2.21.0" />

And in your startup code:

 services.AddApplicationInsightsTelemetry();

For Node.js:

 const appInsights = require('applicationinsights'); appInsights.setup('<your-instrumentation-key>').start();

Verify your application settings include:

• APPLICATIONINSIGHTS_CONNECTION_STRING
• ApplicationInsightsAgent_EXTENSION_VERSION (set to ~3 for latest version)

1. Check these common gotchas:

• Make sure you're using the correct instrumentation key/connection string
• Verify the App Insights SDK version is compatible with your application framework
• Ensure your application has the necessary permissions to send telemetry

The HTTP 401 errors you're seeing in App Service diagnostics are platform-level logs, which is why they appear regardless of application instrumentation. Application Insights, however, needs code-level integration to provide detailed performance metrics, request tracking, and dependency calls.

references:

Application Insights portal connectivity issues - Azure | Microsoft Learn

Troubleshoot problems with Azure Application Insights Profiler - Azure Monitor | Azure Docs