Traceparent option

CHANGELOG.md

@@ -14,6 +14,8 @@ Main (unreleased)
 
 - update promtail converter to use `file_match` block for `loki.source.file` instead of going through `local.file_match`. (@kalleep)
 
+- Added `send_traceparent` option for `tracing` config to enable traceparent header propagation. (@MyDigitalLife)
+
 ### Bugfixes
 
 - `loki.source.api` no longer drops request when relabel rules drops a specific stream. (@kalleep)

docs/sources/reference/config-blocks/tracing.md

@@ -26,9 +26,10 @@ tracing {
 You can use the following arguments with `tracing`:
 
 | Name                | Type                     | Description                                         | Default | Required |
-| ------------------- | ------------------------ | --------------------------------------------------- | ------- | -------- |
+|---------------------|--------------------------|-----------------------------------------------------|---------|----------|
 | `sampling_fraction` | `number`                 | Fraction of traces to keep.                         | `0.1`   | no       |
 | `write_to`          | `list(otelcol.Consumer)` | Inputs from `otelcol` components to send traces to. | `[]`    | no       |
+| `send_traceparent`  | `bool`                   | Send traceparent header with requests.              | `false` | no       |
 
 The `write_to` argument controls which components to send traces to for processing.
 The elements in the array can be any `otelcol` component that accept traces, including processors and exporters.
@@ -42,6 +43,8 @@ The `sampling_fraction` argument controls what percentage of generated traces sh
 When set to `1` or greater, 100% of traces are kept.
 When set to `0` or lower, 0% of traces are kept.
 
+The `send_traceparent` argument controls whether the `traceparent` header is sent with requests to other services.
+
 ## Blocks
 
 You can use the following blocks with `tracing`:
@@ -85,6 +88,7 @@ If the remote sampling strategy exceeds the limit, sampling decisions fall back
 ```alloy
 tracing {
   sampling_fraction = 0.1
+  send_traceparent = true
 
   write_to = [otelcol.exporter.otlp.tempo.input]
 }

internal/runtime/tracing/tracing.go

@@ -11,7 +11,9 @@ import (
 	"github.com/grafana/alloy/internal/build"
 	"github.com/grafana/alloy/internal/component/otelcol"
 	"github.com/grafana/alloy/internal/runtime/tracing/internal/jaegerremote"
+	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/exporters/otlp/otlptrace"
+	"go.opentelemetry.io/otel/propagation"
 	"go.opentelemetry.io/otel/sdk/resource"
 	tracesdk "go.opentelemetry.io/otel/sdk/trace"
 	semconv "go.opentelemetry.io/otel/semconv/v1.37.0"
@@ -25,6 +27,7 @@ var (
 	DefaultOptions = Options{
 		SamplingFraction: 0.1,                  // Keep 10% of spans
 		WriteTo:          []otelcol.Consumer{}, // Don't send spans anywhere.
+		SendTraceparent:  false,
 	}
 
 	DefaultJaegerRemoteSamplerOptions = JaegerRemoteSamplerOptions{
@@ -39,6 +42,7 @@ type Options struct {
 	// SamplingFraction determines which rate of traces to sample. A value of 1
 	// means to keep 100% of traces. A value of 0 means to keep 0% of traces.
 	SamplingFraction float64 `alloy:"sampling_fraction,attr,optional"`
+	SendTraceparent  bool    `alloy:"send_traceparent,attr,optional"`
 
 	// Sampler holds optional samplers to configure on top of the sampling
 	// fraction.
@@ -109,6 +113,8 @@ func New(cfg Options) (*Tracer, error) {
 	var sampler lazySampler
 	sampler.SetSampler(tracesdk.TraceIDRatioBased(cfg.SamplingFraction))
 
+	setOTELTraceContextPropagators(cfg)
+
 	shimClient := &client{}
 	exp := otlptrace.NewUnstarted(shimClient)
 
@@ -136,6 +142,8 @@ func (t *Tracer) Update(opts Options) error {
 	t.samplerMut.Lock()
 	defer t.samplerMut.Unlock()
 
+	setOTELTraceContextPropagators(opts)
+
 	t.client.UpdateWriteTo(opts.WriteTo)
 
 	// Stop the previous instance of the Jaeger remote sampler if it exists. The
@@ -169,6 +177,19 @@ func (t *Tracer) Update(opts Options) error {
 	return nil
 }
 
+func setOTELTraceContextPropagators(opts Options) {
+	var propagators []propagation.TextMapPropagator
+	if opts.SendTraceparent {
+		propagators = append(
+			propagators,
+			propagation.TraceContext{},
+			propagation.Baggage{},
+		)
+	}
+
+	otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(propagators...))
+}
+
 // Run starts the tracing subsystem and runs it until the provided context is
 // canceled. If the tracing subsystem could not be started, an error is
 // returned.