creating Opentelemetry Context using trace-id and span-id of remote parent

Question

I have micro service which support open tracing and that injecting trace-id and span-id in to header. Other micro service support open telemetry. how can I create parent span using trace-id and span-id in second micro service?

Thanks,

Answer 1

Generally you have to propogate the span-id and trace-id if it is available in header. Any request you get in your microservice, check if the headers have span-id and trace-id in them. If yes,extract them and use them in your service. If it is not present then you create a new one and use it in your service and also add it to requests that go out of your microservice.

Answer 2

You can use W3C Trace Context specifications to achieve this. We need to send traceparent(Ex: 00-8652a752089f33e2659dff28d683a18f-7359b90f4355cfd9-01) from producer via HTTP headres ( or you can create it using the trace-id and span-id in the consumer). Then we can extract the remote context and create the span with traceparent.

This is the consumer controller. TextMapGetter used to map that traceparent data to the Context. ExtractModel is just a custom class.

  @GetMapping(value = "/second")
  public String sencondTest(@RequestHeader(value = "traceparent") String traceparent){
    try {
      Tracer tracer = openTelemetry.getTracer("cloud.events.second");

      TextMapGetter<ExtractModel> getter = new TextMapGetter<>() {
        @Override
        public String get(ExtractModel carrier, String key) {
          if (carrier.getHeaders().containsKey(key)) {
            return carrier.getHeaders().get(key);
          }
          return null;
        }

        @Override
        public Iterable<String> keys(ExtractModel carrier) {
          return carrier.getHeaders().keySet();
        }
      };

      ExtractModel model = new ExtractModel();
      model.addHeader("traceparent", traceparent);
      Context extractedContext = openTelemetry.getPropagators().getTextMapPropagator()
              .extract(Context.current(), model, getter);

      try (Scope scope = extractedContext.makeCurrent()) {
        // Automatically use the extracted SpanContext as parent.
        Span serverSpan = tracer.spanBuilder("CloudEvents Server")
                .setSpanKind(SpanKind.SERVER)
                .startSpan();
        try {

          Thread.sleep(150);
        } finally {
          serverSpan.end();
        }
      }

    } catch (InterruptedException e) {
      throw new RuntimeException(e);
    }

    return "Server Received!";
  }

Then when we configuring the OpenTelemetrySdk need to set W3CTraceContextPropagator in Context Propagators.

// Use W3C Propagator(to extract span from HTTP headers) since we use the W3C specifications
TextMapPropagator textMapPropagator = W3CTraceContextPropagator.getInstance();

OpenTelemetrySdk openTelemetrySdk = OpenTelemetrySdk.builder()
        .setTracerProvider(tracerProvider)
        .setPropagators(ContextPropagators.create(textMapPropagator))
        .buildAndRegisterGlobal();

Here is my customer ExtractModel class

public class ExtractModel {

  private Map<String, String> headers;

  public void addHeader(String key, String value) {
    if (this.headers == null){
      headers = new HashMap<>();
    }
    headers.put(key, value);
  }

  public Map<String, String> getHeaders() {
    return headers;
  }

  public void setHeaders(Map<String, String> headers) {
    this.headers = headers;
  }
}

You can find more details in the official documentation for manual instrumentation.