github.com/GoogleCloudPlatform/opentelemetry-operations-go/propagator

OpenTelemetry Google Cloud Trace Propagators

This package contains Trace Context Propagators for use with Google Cloud Trace that make it compatible with OpenTelemetry.

There are two available propagators in this package:

CloudTraceOneWayPropagator (Recommended)

The CloudTraceOneWayPropagator reads the X-Cloud-Trace-Context header for trace and span IDs, but does not write the X-Cloud-Trace-Context header into outgoing requests.

This is useful for ensuring spans created in your code are attached to the traces that some Google Cloud services automatically trace.

Usage

import (
    "go.opentelemetry.io/otel/propagation"
    gcppropagator "github.com/GoogleCloudPlatform/opentelemetry-operations-go/propagator"
)

func installPropagators() {
    otel.SetTextMapPropagator(
        propagation.NewCompositeTextMapPropagator(
            // Putting the CloudTraceOneWayPropagator first means the TraceContext propagator 
            // takes precedence if both the traceparent and the XCTC headers exist.
            gcppropagator.CloudTraceOneWayPropagator{},
            propagation.TraceContext{},
            propagation.Baggage{},
        ))
}

CloudTraceFormatPropagator

The standard propagator reads and writes the X-Cloud-Trace-Context header. Note that because of differences between the meaning of the sampled flag (described below), this can result in 100% tracing when the parent context has a deferred tracing decision.

Usage

import (
    "go.opentelemetry.io/otel/propagation"
    gcppropagator "github.com/GoogleCloudPlatform/opentelemetry-operations-go/propagator"
)

func installPropagators() {
    otel.SetTextMapPropagator(
        propagation.NewCompositeTextMapPropagator(
            // Putting the CloudTraceFormatPropagator first means the TraceContext propagator 
            // takes precedence if both the traceparent and the XCTC headers exist.
            gcppropagator.CloudTraceFormatPropagator{},
            propagation.TraceContext{},
            propagation.Baggage{},
        ))
}

Differences between Google Cloud Trace and W3C Trace Context

Google Cloud Trace encodes trace information in the X-Cloud-Trace-Context HTTP header, using the format described in the Trace documentation.

OpenTelemetry uses the newer, W3C standard traceparent header

There is an important semantic difference between Cloud Trace's TRACE_TRUE flag, and W3C's sampled flag.

As outlined in the Trace documentation, setting the TRACE_TRUE flag will cause trace information to be collected.

This differs from the W3C behavior, where the sampled flag indicates that the caller may have recorded trace information, but does not necessarily impact the sampling done by other services.

To preserve the Cloud-Trace behavior when using traceparent, you can use the ParentBased sampler like so:

import sdktrace go.opentelemetry.io/otel/sdk/trace
sampler := sdktrace.ParentBased(
    sdktrace.NeverSample(),
    sdktrace.WithRemoteParentSampled(sdktrace.AlwaysSample()))
)