ASP.NET Core + W3C TraceContext

Mapping

// Mapping of .NET Activity Context to W3C TraceContext
var traceId = Activity.Current!.ParentId; // W3C 3.2.2.3 trace-id
var parentId = Activity.Current!.ParentSpanId; // W3C 3.2.2.4 parent-id
var spanId = Activity.Current!.SpanId; // This service's span-id. Will become parent-id of next call

Program.cs

// The W3C says that a span is the execution of a client request (chapter 3.2.2.4). By default, .NET creates a span for each created (internal) activity.
// This can lead to traceparent headers containing span-ids whose placement in the execution flow is not possible.
// Since .NET6, DistributedContextPropagators can be used to control the creation of the traceparent header. Use the built-in PassThroughPropagator that sets the incoming span-id as parent-id and not the id of the latest activity.
// Details at https://devblogs.microsoft.com/dotnet/dotnet-6-networking-improvements/#diagnostics
DistributedContextPropagator.Current = DistributedContextPropagator.CreatePassThroughPropagator();

// Activate W3C compatible headers.
// Details at https://devblogs.microsoft.com/dotnet/improvements-in-net-core-3-0-for-troubleshooting-and-monitoring-distributed-apps/#w3c-trace-context-support
Activity.DefaultIdFormat = ActivityIdFormat.W3C;