.NET Custom Instrumentation using OpenTelemetry API

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Unsure when to use OpenTelemetry with Datadog? Start with Custom Instrumentation with the OpenTelemetry API to learn more.

Overview

There are a few reasons to manually instrument your applications with the OpenTelemetry API:

You are not using Datadog supported library instrumentation.
You want to extend the ddtrace library’s functionality.
You need finer control over instrumenting your applications.

The ddtrace library provides several techniques to help you achieve these goals. The following sections demonstrate how to use the OpenTelemetry API for custom instrumentation to use with Datadog.

Setup

To configure OpenTelemetry to use the Datadog trace provider:

Add your desired manual OpenTelemetry instrumentation to your .NET code following the OpenTelemetry .NET Manual Instrumentation documentation. Note: Where those instructions indicate that your code should call the OpenTelemetry SDK, call the Datadog tracing library instead.
Install the Datadog .NET tracing library and enable the tracer for your .NET Framework service or your .NET Core (and .NET 5+) service. Beta: You can optionally do this with Single Step APM Instrumentation.
Set DD_TRACE_OTEL_ENABLED environment variable to true.
Run your application.

Datadog combines these OpenTelemetry spans with other Datadog APM spans into a single trace of your application. It also supports OpenTelemetry instrumentation libraries.

Creating custom spans

To manually create spans that start a new, independent trace:

using OpenTelemetry.Resources;
using OpenTelemetry.Trace;

// Start a new span
using (Activity? activity = Telemetry.ActivitySource.StartActivity("<RESOURCE NAME>"))
            {
  activity?.SetTag("operation.name", "custom-operation");
               // Do something
            }

Creating spans

To create custom spans within an existing trace context:

using OpenTelemetry.Resources;
using OpenTelemetry.Trace;

using (Activity? parentScope = Telemetry.ActivitySource.StartActivity("<RESOURCE NAME>"))
{
   parentScope?.SetTag("operation.name", "manual.sortorders");
   using (Activity? childScope = Telemetry.ActivitySource.StartActivity("<RESOURCE NAME>"))
   {
       // Nest using statements around the code to trace
       childScope?.SetTag("operation.name", "manual.sortorders.child");
       SortOrders();
   }
}

Adding span tags

Add custom tags to your spans to provide additional context:

using OpenTelemetry.Resources;
using OpenTelemetry.Trace;

public class ShoppingCartController : Controller
{
    private IShoppingCartRepository _shoppingCartRepository;

    [HttpGet]
    public IActionResult Index(int customerId)
    {
      Activity? activity =
      Telemetry.ActivitySource.StartActivity("<RESOURCE NAME>")

        // Add a tag to the span for use in the Datadog web UI
        activity?.SetTag("customer.id", customerId.ToString());

        var cart = _shoppingCartRepository.Get(customerId);

        return View(cart);
    }
}

Setting errors on spans

Set error information on a span when an error occurs during its execution.

try
{
    // do work that can throw an exception
}
catch(Exception e)
{
    activity?.SetTag("error", 1);
    activity?.SetTag("error.msg", exception.Message);
    activity?.SetTag("error.stack", exception.ToString());
    activity?.SetTag("error.type", exception.GetType().ToString());
}

Propagating context with headers extraction and injection

You can configure the propagation of context for distributed traces by injecting and extracting headers. Read Trace Context Propagation for information.