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Application Insights logging with .NET

  • Article
  • 5 minutes to read

In this article, you'll learn how to capture logs with Application Insights in .NET apps by using the Microsoft.Extensions.Logging.ApplicationInsights provider package. If you use this provider, you can query and analyze your logs by using the Application Insights tools.

Note

If you want to implement the full range of Application Insights telemetry along with logging, see Configure Application Insights for your ASP.NET websites or Application Insights for ASP.NET Core applications.

Tip

The Microsoft.ApplicationInsights.WorkerService NuGet package, used to enable Application Insights for background services, is out of scope. For more information, see Application Insights for Worker Service apps.

ASP.NET Core applications

To add Application Insights logging to ASP.NET Core applications:

  1. Install the Microsoft.Extensions.Logging.ApplicationInsights.

  2. Add ApplicationInsightsLoggerProvider:

using Microsoft.Extensions.Logging.ApplicationInsights;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.

builder.Services.AddControllers();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

builder.Logging.AddApplicationInsights(
        configureTelemetryConfiguration: (config) => 
            config.ConnectionString = builder.Configuration.GetConnectionString("APPLICATIONINSIGHTS_CONNECTION_STRING"),
            configureApplicationInsightsLoggerOptions: (options) => { }
    );

builder.Logging.AddFilter<ApplicationInsightsLoggerProvider>("your-category", LogLevel.Trace);

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

app.Run();

With the NuGet package installed, and the provider being registered with dependency injection, the app is ready to log. With constructor injection, either ILogger or the generic-type alternative ILogger<TCategoryName> is required. When these implementations are resolved, ApplicationInsightsLoggerProvider will provide them. Logged messages or exceptions will be sent to Application Insights.

Consider the following example controller:

public class ValuesController : ControllerBase
{
    private readonly ILogger _logger;

    public ValuesController(ILogger<ValuesController> logger)
    {
        _logger = logger;
    }

    [HttpGet]
    public ActionResult<IEnumerable<string>> Get()
    {
        _logger.LogWarning("An example of a Warning trace..");
        _logger.LogError("An example of an Error level message");

        return new string[] { "value1", "value2" };
    }
}

For more information, see Logging in ASP.NET Core.

Console application

To add Application Insights logging to console applications, first install the following NuGet packages:

The following example uses the Microsoft.Extensions.Logging.ApplicationInsights package and demonstrates the default behavior for a console application. The Microsoft.Extensions.Logging.ApplicationInsights package should be used in a console application or whenever you want a bare minimum implementation of Application Insights without the full feature set such as metrics, distributed tracing, sampling, and telemetry initializers.

using Microsoft.ApplicationInsights.Channel;
using Microsoft.ApplicationInsights.Extensibility;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;

using var channel = new InMemoryChannel();

try
{
    IServiceCollection services = new ServiceCollection();
    services.Configure<TelemetryConfiguration>(config => config.TelemetryChannel = channel);
    services.AddLogging(builder =>
    {
        // Only Application Insights is registered as a logger provider
        builder.AddApplicationInsights(
            configureTelemetryConfiguration: (config) => config.ConnectionString = "<YourConnectionString>",
            configureApplicationInsightsLoggerOptions: (options) => { }
        );
    });

    IServiceProvider serviceProvider = services.BuildServiceProvider();
    ILogger<Program> logger = serviceProvider.GetRequiredService<ILogger<Program>>();

    logger.LogInformation("Logger is working...");
}
finally
{
    // Explicitly call Flush() followed by Delay, as required in console apps.
    // This ensures that even if the application terminates, telemetry is sent to the back end.
    channel.Flush();

    await Task.Delay(TimeSpan.FromMilliseconds(1000));
}

Frequently asked questions

Why do some ILogger logs not have the same properties as others?

Application Insights captures and sends ILogger logs by using the same TelemetryConfiguration information that's used for every other telemetry. But there's an exception. By default, TelemetryConfiguration isn't fully set up when you log from Program.cs or Startup.cs. Logs from these places won't have the default configuration, so they won't be running all TelemetryInitializer instances and TelemetryProcessor instances.

I'm using the standalone package Microsoft.Extensions.Logging.ApplicationInsights, and I want to log more custom telemetry manually. How should I do that?

When you use the standalone package, TelemetryClient isn't injected to the dependency injection (DI) container. You need to create a new instance of TelemetryClient and use the same configuration that the logger provider uses, as the following code shows. This requirement ensures that the same configuration is used for all custom telemetry and telemetry from ILogger.

public class MyController : ApiController
{
   // This TelemetryClient instance can be used to track additional telemetry through the TrackXXX() API.
   private readonly TelemetryClient _telemetryClient;
   private readonly ILogger _logger;

   public MyController(IOptions<TelemetryConfiguration> options, ILogger<MyController> logger)
   {
        _telemetryClient = new TelemetryClient(options.Value);
        _logger = logger;
   }  
}

Note

If you use the Microsoft.ApplicationInsights.AspNetCore package to enable Application Insights, modify this code to get TelemetryClient directly in the constructor. For an example, see this FAQ.

What Application Insights telemetry type is produced from ILogger logs? Where can I see ILogger logs in Application Insights?

ApplicationInsightsLoggerProvider captures ILogger logs and creates TraceTelemetry from them. If an Exception object is passed to the Log method on ILogger, ExceptionTelemetry is created instead of TraceTelemetry.

These telemetry items can be found in the same places as any other TraceTelemetry or ExceptionTelemetry items for Application Insights, including the Azure portal, analytics, or the Visual Studio local debugger.

If you prefer to always send TraceTelemetry, use this snippet:

builder.AddApplicationInsights(
    options => options.TrackExceptionsAsExceptionTelemetry = false);

I don't have the SDK installed, and I use the Azure Web Apps extension to enable Application Insights for my ASP.NET Core applications. How do I use the new provider?

The Application Insights extension in Azure Web Apps uses the new provider. You can modify the filtering rules in the appsettings.json file for your application.

Next steps