Starting a span with a given trace ID

[burgerj03]

Is it possible to start a new span with a given trace ID. I was hoping to use a trace ID generated by another framework?

[legendecas]

You can checkout the TracerOption#idGenerator and implement one of your own: https://open-telemetry.github.io/opentelemetry-js/interfaces/_opentelemetry_sdk_trace_base.TracerConfig.html#idGenerator

[burgerj03]

Thanks for replying so quickly.

We're not sure if our use case is valid, but we need to specify the trace ID when we call https://open-telemetry.github.io/opentelemetry-js/classes/_opentelemetry_sdk_trace_base.Tracer.html#startSpan. At that point, we have an externally obtained correlation ID we would like to pass in. This correlation ID allows us to weave all related spans (even the ones coming in via a message broker).

I'm not sure if overriding the idGenerator will allow us to specify an ID each time a span is created. Is there another way for me to create a span?

[burgerj03]

Just an update, here's the approach we plan to take:

const externalContext = trace.setSpan(
      ROOT_CONTEXT,
      trace.wrapSpanContext({
        traceId: externalTraceId
        spanId: normalisedSpanId,
        isRemote: true,
        traceFlags: TraceFlags.SAMPLED,
      })
    );
const span = this.opentelemetryTracer.startSpan(
      span.name,
      undefined,
      externalContext
    );

[Flarna]

This could work to get the TraceID in. But the new span will refer to normalisedSpanId as parent and I assume there is no such span exported to your backend.
Therefore your backend may complain about incomplete traces.

The intention of IdGenerator is to replace the random generator and not to inject specific "random" ids. As javascript is sync it's most likely not that hard to implement an ID generator which gets a TraceId set to return on next call and in all other cases return a real random. But that is not really the intention of the design as TraceIds should be random or taken from parent.