Adding OpenTelemetry to a .NET Core Application

.NET Core is widely used for building modern, cross-platform backend services and web applications. With performance, scalability, and reliability at stake, teams need real visibility into how their applications are running. This means going beyond simple logs—true observability requires metrics and traces.

OpenTelemetry (OTel) makes this possible. It's an open standard for collecting telemetry data—logs, metrics, and traces—in a consistent, vendor-neutral way. With OTel, you can track performance issues, monitor dependencies, and analyze runtime behavior across your entire stack.

In this guide, we’ll walk through how to instrument a .NET Core application with OTel. You’ll see how to capture metrics and trace data, and export that telemetry to SolarWinds® Observability SaaS for visualization and analysis.

Download and Run the Sample Application

To get started, we’ll use the Razor Pages movie listing app from Microsoft’s ASP.NET Core tutorials. This gives us a clean, functional project to work with.

First, download the sample application. You can also check out the official Microsoft Learn instructions. Make sure you have downloaded and installed the .NET 9.0 SDK.

For this basic demo, you will build and run the app locally. This means modifying the application to use SQLite.

Modifications for Local Demo (Use SQLite)

First, add this line <ItemGroup> in  RazorPagesMovie.csproj:

<PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="9.0.0-preview.3.24172.4" />

Next, modify Program.cs to accommodate the SQLite case. The resulting file looks like this:

using Microsoft.EntityFrameworkCore; using RazorPagesMovie.Data; using RazorPagesMovie.Models; var builder = WebApplication.CreateBuilder(args); // Set environment to Development builder.Environment.EnvironmentName = "Development"; builder.Services.AddRazorPages(); builder.Services.AddDbContext<RazorPagesMovieContext>(options =>     options.UseSqlite(builder.Configuration.GetConnectionString("RazorPagesMovieContext") ?? throw new InvalidOperationException("Connection string 'RazorPagesMovieContext' not found."))); var app = builder.Build(); using (var scope = app.Services.CreateScope()) {   var services = scope.ServiceProvider;   SeedData.Initialize(services); } // Always use developer exception page in development if (app.Environment.IsDevelopment()) {   app.UseDeveloperExceptionPage(); } else {   app.UseExceptionHandler("/Error");   app.UseHsts(); } app.UseHttpsRedirection(); app.UseStaticFiles(); app.UseRouting(); app.UseAuthorization(); app.MapRazorPages(); app.Run();

Finally, modify appsettings.json to point to the correct data source file:

{   "Logging": {     "LogLevel": {       "Default": "Information",       "Microsoft.AspNetCore": "Warning"     }   },   "AllowedHosts": "*",   "ConnectionStrings": {     "RazorPagesMovieContext": "Data Source=RazorPagesMovie.db"   } }

With these file changes in place, go ahead and run the following commands:

rm -rf Migrations/ dotnet ef migrations add InitialCreate dotnet ef database update dotnet run

Now, when you open your browser to localhost:5000, you’ll see the application running:

Configure the Application for OpenTelemetry

Before instrumenting the app, you need to add OTel-related dependencies to your project.

Add OpenTelemetry Packages

Use dotnet add package to install the necessary OTel packages:

dotnet add package OpenTelemetry.Extensions.Hosting

dotnet add package OpenTelemetry.Instrumentation.AspNetCore

dotnet add package OpenTelemetry.Instrumentation.Runtime

dotnet add package OpenTelemetry.Exporter.OpenTelemetryProtocol

dotnet add package OpenTelemetry.Extensions.Logging 

dotnet add package OpenTelemetry.Instrumentation.Http

dotnet add package OpenTelemetry.Instrumentation.SqlClient

Next, modify Program.cs to set up the OTel services and configure the OTLP exporter to send data to SolarWinds Observability SaaS:

// Program.cs

using Microsoft.EntityFrameworkCore; using OpenTelemetry; using OpenTelemetry.Logs; using OpenTelemetry.Metrics; using OpenTelemetry.Resources; using OpenTelemetry.Trace;

using OpenTelemetry.Instrumentation.SqlClient;

using RazorPagesMovie.Data; using RazorPagesMovie.Models; var builder = WebApplication.CreateBuilder(args);

// Add OpenTelemetry configuration

builder.Configuration.AddJsonFile("appsettings.OpenTelemetry.json", optional: false, reloadOnChange: true);

// Set environment to Development builder.Environment.EnvironmentName = "Development"; // Configure OpenTelemetry var otelConfig = builder.Configuration.GetSection("OpenTelemetry"); var serviceName = otelConfig["ServiceName"] ?? "RazorPagesMovie"; var serviceVersion = otelConfig["ServiceVersion"] ?? "1.0.0"; var solarWindsEndpoint = otelConfig.GetSection("SolarWinds")["Endpoint"]; var solarWindsToken = otelConfig.GetSection("SolarWinds")["ApiToken"]; if (string.IsNullOrEmpty(solarWindsEndpoint) || string.IsNullOrEmpty(solarWindsToken)) {   throw new InvalidOperationException("SolarWinds endpoint and API token must be configured in appsettings.OpenTelemetry.json"); } builder.Services.AddOpenTelemetry()

  .ConfigureResource(resource => resource

    .AddService(serviceName: serviceName, serviceVersion: serviceVersion))

  .WithTracing(tracing => tracing

    .AddAspNetCoreInstrumentation()

    .AddHttpClientInstrumentation()

    .AddSqlClientInstrumentation()

    .AddOtlpExporter(opts => {

      opts.Endpoint = new Uri(solarWindsEndpoint);

      opts.Headers = $"authorization=Bearer {solarWindsToken}";

    }))

  .WithMetrics(metrics => metrics

    .AddAspNetCoreInstrumentation()

    .AddHttpClientInstrumentation()

    .AddRuntimeInstrumentation()

    .AddOtlpExporter(opts => {

      opts.Endpoint = new Uri(solarWindsEndpoint);

      opts.Headers = $"authorization=Bearer {solarWindsToken}";

    }));

// Configure OpenTelemetry Logging

builder.Logging.AddOpenTelemetry(logging =>

{

  logging.IncludeFormattedMessage = true;

  logging.IncludeScopes = true;

  logging.ParseStateValues = true;

  logging.AddOtlpExporter(opts => {

    opts.Endpoint = new Uri(solarWindsEndpoint);

    opts.Headers = $"authorization=Bearer {solarWindsToken}";

  });

});

builder.Services.AddRazorPages();

...

Next, configure your application with the credentials to send OTel data to SolarWinds Observability SaaS.

Get SolarWinds Observability SaaS OTel Endpoint and API Token

To find your OTel endpoint and create an API token for data ingestion, follow these steps.

<a id="" style="background-color:#fff0cf;" href="https://my.na-01.cloud.solarwinds.com/">https://my.na-01.cloud.solarwinds.com/</a>

The xx-yy part of the URL (in the above example, that's na-01) indicates the data center for your organization. You will need this when determining your OTel endpoint.

Navigate to Settings > API Tokens.

On the API Tokens page, click Create API Token.

Specify a name for your new API token. Select Ingestion as the token type. You can also add tags if you'd like. Click Create API Token.

Copy the resulting token value.

Configure OTel Export Settings

Next, create a new configuration file (appsettings.OpenTelemetry.json) to store the SolarWinds Observability SaaS endpoint and API token.

{   "OpenTelemetry": {     "ServiceName": "RazorPagesMovie",     "ServiceVersion": "1.0.0",     "SolarWinds": {       "Endpoint": "https://otel.collector.xx-yy.cloud.solarwinds.com:443",       "ApiToken": "YOUR_API_TOKEN_HERE"     }   } }

Replace the xx-yy in the endpoint with your data center code (such as na-01). Then, paste in the API token value that was just copied.

Lastly, update the project file (RazorPagesMovie.csproj) to include this configuration file:

<ItemGroup>

  …   <None Update="appsettings.OpenTelemetry.json">     <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>   </None> </ItemGroup>

Instrument the Application

With the application configured with OTel and ready to collect and send telemetry data to SolarWinds Observability SaaS, you're ready to instrument the application.

Logging Middleware and Telemetry Helpers

For convenience, create a class (Middleware/RequestLoggingMiddleware.cs) so that you can log every request:

// Middleware/RequestLoggingMiddleware.cs

         "Request {Method} {Path} completed with status code {StatusCode} in {ElapsedMilliseconds}ms",         method, path, statusCode, elapsed

      );     }   } }

Next, create a class (Telemetry/TelemetryHelper.cs) to implement custom traces and metrics.

using System.Diagnostics; using System.Diagnostics.Metrics; using OpenTelemetry.Trace; using Microsoft.Extensions.Configuration; namespace RazorPagesMovie.Telemetry; public static class TelemetryHelper {   private static readonly ActivitySource ActivitySource;   private static readonly Meter Meter;       // Metrics   private static readonly Counter<long> MovieOperationCounter;   private static readonly Histogram<double> MovieOperationDuration;   static TelemetryHelper()   {     var configuration = new ConfigurationBuilder()       .AddJsonFile("appsettings.OpenTelemetry.json", optional: false)       .Build();                   var serviceName = configuration.GetSection("OpenTelemetry")["ServiceName"] ?? "RazorPagesMovie";               ctivitySource = new ActivitySource(serviceName);       Meter = new Meter(serviceName);               MovieOperationCounter = Meter.CreateCounter<long>(         "movie_operations_total",         "operations",         "Total number of movie operations performed");               MovieOperationDuration = Meter.CreateHistogram<double>(         "movie_operation_duration_seconds",         "seconds",         "Duration of movie operations");   }   public static Activity? StartMovieOperation(string operation, int? movieId = null)   {     var activity = ActivitySource.StartActivity($"Movie.{operation}");     if (activity != null)     {       activity.SetTag("movie.operation", operation);       if (movieId.HasValue)       {         activity.SetTag("movie.id", movieId.Value);       }     }   return activity;   }   public static void RecordMovieOperation(string operation, double durationSeconds, int? movieId = null)   {     var tags = new KeyValuePair<string, object?>[]     {       new("operation", operation)     };     if (movieId.HasValue)     {       tags = tags.Append(new KeyValuePair<string, object?>("movie.id", movieId.Value)).ToArray();     }     MovieOperationCounter.Add(1, tags);     MovieOperationDuration.Record(durationSeconds, tags);   } }

Back in Program.cs, register your middleware and telemetry components.

// Program.cs

… builder.Services.AddOpenTelemetry()

  .ConfigureResource(resource => resource

    .AddService(serviceName: serviceName, serviceVersion: serviceVersion))

  .WithTracing(tracing => tracing

    .AddAspNetCoreInstrumentation()

    .AddHttpClientInstrumentation()

    .AddSqlClientInstrumentation()

    .AddSource(serviceName)

    .AddOtlpExporter(opts => {

      opts.Endpoint = new Uri(solarWindsEndpoint);

      opts.Headers = $"authorization=Bearer {solarWindsToken}";

    }))

  .WithMetrics(metrics => metrics

    .AddAspNetCoreInstrumentation()

    .AddHttpClientInstrumentation()

    .AddRuntimeInstrumentation()

    .AddMeter(serviceName)

    .AddOtlpExporter(opts => {

      opts.Endpoint = new Uri(solarWindsEndpoint);

      opts.Headers = $"authorization=Bearer {solarWindsToken}";

    }));

… app.UseMiddleware<RequestLoggingMiddleware>();

Set up Tracing and Metrics

Finally, throughout the application, add instrumentation code. For example, in the Create movie operation, you can capture request duration metrics.

// Pages/Movies/Create.cshtml.cs

public async Task<IActionResult> OnPostAsync() {   var sw = Stopwatch.StartNew();   using var activity = TelemetryHelper.StartMovieOperation("Create");               try   {     if (!ModelState.IsValid)     {       return Page();     }     _context.Movie.Add(Movie);     await _context.SaveChangesAsync();                     _logger.LogInformation("Created movie: {Title}", Movie.Title);     TelemetryHelper.RecordMovieOperation("Create", sw.Elapsed.TotalSeconds);                     return RedirectToPage("./Index");   }   catch (Exception ex)   {     _logger.LogError(ex, "Error creating movie: {Title}", Movie.Title);     activity?.SetStatus(ActivityStatusCode.Error, ex.Message);     throw;   }

}

Your application is now instrumented with OTel across all three pillars:

Logging: HTTP requests (via RequestLoggingMiddleware) and movie operations (in page models)
Traces: HTTP/SQL operations (automatic) and movie operations (via TelemetryHelper)
Metrics: Runtime/HTTP metrics (automatic) and movie operation counts/durations (via TelemetryHelper)

All telemetry is exported to SolarWinds with consistent service naming and proper authentication. You're ready to start it up again.

dotnet run

This time, with the application running, try performing different operations and transactions to simulate activity and generate telemetry data.

Confirm Data Ingestion With SolarWinds Observability SaaS

To confirm that your application is successfully sending telemetry data to SolarWinds Observability SaaS, log in to your account and navigate to APM.

There, you should see your application listed.

Clicking the application brings you to an APM overview page for your application. You’ll see the presence of traces (50+) and metrics (4) just by looking at the top bar nav.

The Traces subpage shows the custom spans that you have instrumented for tracing in your application's Movie model.

When you click on the details for any individual trace, you’ll see detailed information about the times spent in each of the components throughout the action.

Similarly, you can visit the Metrics subpage for your application. From there, you can see metrics, such as the average response time.

Finally, to see log events captured with OTel and exported to SolarWinds Observability SaaS, navigate to the Logs section of the site.

On that page, there’s a comprehensive set of log events, from your request middleware, explicit logging statements in your Movie actions, and within your database operations.

You have successfully instrumented your .NET Core application with OTel, and your telemetry data is shipping to SolarWinds Observability SaaS for easier analysis and querying.

Wrap-up and Next Steps

We’ve shown how to instrument a .NET Core app with OpenTelemetry to capture logs, metrics, and traces. By using open standards, you can make your observability setup portable and extensible—there is no vendor lock-in.

If you’re looking for a powerful and user-friendly way to analyze and visualize your telemetry data, check out SolarWinds Observability SaaS. It’s built to work seamlessly with OTel and supports a wide range of application stacks, including .NET Core.

 

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Comments

donrobert5

\m/

jgoetsch

Any advice for API token rejection during this process?

Rachel.Revoy

API token rejection might be related to a configuration gotcha. Here are a few things you can check:

Make sure you obtained an "Ingestion" token from SolarWinds.
Make sure the token is still active in your API Tokens settings.
It might be a copy-paste issue. Sometimes you accidentally grab extra whitespace or miss part of the token. Make sure you have copied the token correctly.
Check that configured your endpoint URL has the right data center code (like "na-01") that matches what you see in your SolarWinds dashboard URL.
Check the authorization header format in your .NET code. It needs to be exactly "authorization=Bearer {your_token}". It's easy to accidentally include "Bearer" as part of the token itself when copying from documentation.

Hope this helps!