Microsoft Applicationinsights Dotnet Applicationinsights Dotnet

Application Insights Setup

This skill detects your .NET application type and instrumentation state, then guides you through the correct setup, migration, or enhancement path.

Step 1 — Detect Application Type

Find all .csproj files (also .fsproj, .vbproj) in the workspace. If multiple non-library projects exist, ask the user which one to instrument before proceeding. Also check for global.json as a .NET workspace indicator.

First, check the <Project Sdk="..."> attribute in the .csproj:

SDK-style projects (modern format — has Sdk attribute)

For ASP.NET Core / Worker Service, read Program.cs (or Startup.cs in older projects) to confirm hosting pattern:

• WebApplication.CreateBuilder → ASP.NET Core minimal APIs
• Host.CreateDefaultBuilder or Host.CreateApplicationBuilder → Generic Host
• CreateWebHostBuilder / WebHost.CreateDefaultBuilder → Legacy ASP.NET Core host

Legacy projects (no Sdk attribute — old .csproj format)

If the <Project> element has no Sdk attribute, this is a legacy .NET Framework project. Detect the type using file and reference patterns:

For ASP.NET Classic, further sub-type (all use the same setup):

• Microsoft.AspNet.Mvc package + Controllers/ folder → ASP.NET MVC
• .aspx or .ascx files → ASP.NET WebForms
• Otherwise → ASP.NET Classic (generic)

Entry point: ASP.NET Classic uses Global.asax.cs as its entry point (not Program.cs).

Step 2 — Detect Existing Instrumentation

Check multiple sources for evidence of existing instrumentation:

Source 1 — Package references: Scan PackageReference nodes in .csproj (check both Version and VersionOverride attributes for central package management). For legacy projects, scan <package> elements in packages.config. Version check: major version ≥ 3 → target version; handles wildcards (3.*), pre-release suffixes, and v prefix.

Source 2 — Config files: Check for applicationinsights.config (its presence indicates existing Classic SDK). Scan appsettings*.json for InstrumentationKey or ApplicationInsights sections.

Detection priority (if multiple types found): Application Insights SDK > plain OpenTelemetry.

Step 3 — Route to the Correct Guide

Greenfield (No existing Application Insights)

Before making any code changes, read references/opentelemetry-pipeline.md to understand the architecture.

Then follow the guide for your app type (all greenfield paths use Application Insights 3.x SDK):

• ASP.NET Core → read references/aspnetcore-greenfield.md
• Worker Service → read references/workerservice-greenfield.md
• ASP.NET Classic → read references/aspnet-classic-greenfield.md
• Console App → read references/console-setup.md

Migration (Application Insights 2.x → 3.x)

First, read references/opentelemetry-pipeline.md to understand how 3.x differs from 2.x.

Then scan the codebase using the template in references/analysis-template.md. This identifies which migration guides are relevant.

Based on findings, read the applicable migration references:

• All migrations: start with references/code-migration.md (property changes, removed APIs)
• ITelemetryInitializer found → references/initializer-migration.md
• ITelemetryProcessor found → references/processor-migration.md
• Custom sampling → references/sampling-migration.md
• ILogger / logging config → references/ilogger-migration.md
• TelemetryClient breaking changes → references/telemetryclient-migration.md
• Dependency tracking config → references/dependency-tracking.md
• AAD / Token Credential authentication → references/aad-authentication-migration.md
• Live Metrics config → references/live-metrics-migration.md

If the scan finds NO code changes needed (only unchanged properties used, no removed APIs), the migration is just a package upgrade — read references/no-code-change-migration.md. Note: this path does NOT apply to Classic ASP.NET — Classic always requires config changes.

Classic ASP.NET migration extras: In addition to the references above, Classic ASP.NET brownfield migration requires:

• Rewrite applicationinsights.config to 3.x format: remove <TelemetryInitializers>, <TelemetryModules>, <TelemetryProcessors>, <TelemetryChannel> sections; replace <InstrumentationKey> with <ConnectionString>
• Update Web.config: remove TelemetryCorrelationHttpModule; verify ApplicationInsightsHttpModule and TelemetryHttpModule are present in <system.webServer><modules>
• Remove satellite packages in order: Microsoft.ApplicationInsights.WindowsServer, .WindowsServer.TelemetryChannel, .DependencyCollector, .PerfCounterCollector, .Agent.Intercept, Microsoft.AspNet.TelemetryCorrelation
• Replace TelemetryConfiguration.Active with TelemetryConfiguration.CreateDefault()
• Connection string goes in ApplicationInsights.config <ConnectionString> element (not appsettings.json)
• Use config.ConfigureOpenTelemetryBuilder(otel => ...) for all extensibility (DI-based methods are not available)

Enhancement (Already on 3.x)

Ask the user what they want to add, then read the relevant reference.

DI vs Non-DI: The enhancement references show DI patterns (builder.Services.Configure*). For Console or Classic ASP.NET apps that use TelemetryConfiguration directly, replace builder.Services.ConfigureOpenTelemetryTracerProvider(tracing => ...) with config.ConfigureOpenTelemetryBuilder(otel => otel.WithTracing(tracing => ...)). Each reference file includes a "Non-DI Usage" section.

• Entity Framework Core → references/entity-framework.md
• Redis (StackExchange.Redis) → references/redis-cache.md
• SQL Client → references/sql-client.md
• HTTP Client/Server Enrichment → references/http-instrumentation.md
• OTLP Exporter → references/otlp-exporter.md
• Console Exporter (dev/debug only) → OpenTelemetry.Exporter.Console package, .AddConsoleExporter() on each signal
• Sampling Configuration → references/sampling-migration.md (applies to enhancement too)
• Custom Processors (filtering/enrichment) → references/custom-processors.md
• Custom Activities (distributed tracing) → references/custom-activities.md
• Custom Logging (ILogger best practices) → references/custom-logging.md
• Custom Metrics → references/custom-metrics.md

Important Rules

1. Learn first, act second: Always read the relevant concept or migration reference BEFORE making code changes.
2. Connection string, not instrumentation key: Always use ConnectionString, never InstrumentationKey. The environment variable is APPLICATIONINSIGHTS_CONNECTION_STRING. For Classic ASP.NET, connection string goes in ApplicationInsights.config, not appsettings.json.
3. Application Insights 3.x SDK only: This skill covers Microsoft.ApplicationInsights.AspNetCore / .WorkerService / .Web. The Azure Monitor OpenTelemetry Distro (Azure.Monitor.OpenTelemetry.AspNetCore) is a separate product — do not mix them, and do not use this skill for Distro-based apps.
4. Classic ASP.NET uses Package Manager Console: Use Install-Package in Visual Studio, not dotnet add package.
5. Verify after changes: Build the project, run it, and confirm telemetry appears in Azure Portal (Live Metrics for immediate feedback, Transaction Search for 2-5 minute delayed data).
6. Unsupported app types: If the detected type is WCF Service, OWIN App, or Azure Functions, inform the user that automated setup is not available and point them to the Azure Monitor documentation for manual onboarding.
7. Error handling: If no .csproj/.fsproj/.vbproj files are found, report that no .NET project was detected rather than guessing.

Examples

Example queries that should use this skill:

• "Add Application Insights to my app"
• "Set up Azure Monitor telemetry"
• "Add observability to my ASP.NET Core project"
• "Migrate from Application Insights 2.x to 3.x"
• "Upgrade my Application Insights SDK"
• "I'm getting deprecated API warnings from Application Insights"
• "Add Redis monitoring to my app that already has Application Insights"
• "How do I add Entity Framework telemetry"
• "Set up OTLP exporter alongside Application Insights"

Troubleshooting

No telemetry appearing: Check that APPLICATIONINSIGHTS_CONNECTION_STRING is set or connection string is configured in appsettings.json. Verify the app targets net8.0 or later for ASP.NET Core 3.x packages.

Package version conflicts: Ensure all Microsoft.ApplicationInsights.* packages are on the same major version. Do not mix 2.x and 3.x packages.

Build errors after migration: Check for removed APIs listed in references/code-migration.md. Common: InstrumentationKey property, ITelemetryInitializer, ITelemetryProcessor, TrackPageView.

Source: microsoft/ApplicationInsights-dotnet — distributed by TomeVault.