Set span parent for all exported spans in SimpleSpanProcessor

[kristijanstefanoski]

I am trying to open a 'root' span and I'd like everything that is exported from that point onward to be nested under the 'root' span.
To achieve this I tried modifying the OTLPTraceExporter like so:

class CustomExporter extends OTLPTraceExporter {
  export(items, resultCallback) {
    items = items.map((span) => {
      const result = Object.create(span);
      result.parentSpanId = span.attributes.isRoot
        ? span.parentSpanId
        : window.rootSpan.spanContext().spanId; // 6b07cadce862131f is root span ID for example

      return result;
    });
    console.log(items[0].parentSpanId, items[0].attributes.isRoot); // Logs 6b07cadce862131f for each, undefined for root
    return super.export(items, (result) => {
      console.log(result); // {code:0}
    });
  }
}

Than I use this exporter:

  const exporter = new CustomExporter();
  provider.addSpanProcessor(new SimpleSpanProcessor(exporter));

rootSpan is started on application bootstrap and in this cases ended 5 seconds later using setTimeout:

const rootSpan = tracer.startActiveSpan("root-span", (span) => {
  window.rootSpan = span;
  span.setAttribute("isRoot", true);
  console.log("root span id:", window.rootSpan.spanContext().spanId); // 6b07cadce862131f

  setTimeout(() => {
    span.end();
    window.rootSpan = null;
    console.log("ended root span");
  }, 5000);
});

But when I modify OTLPTraceExporter like this I can see in the console all the spans have:
parentSpanId: "6b07cadce862131f"
And also the root span has parentSpanId: undefined
And as a result in Jaeger it is still reporting two separate traces, one is the root span and one is for example the document load from the auto instrumentation with 30+ spans inside
There is also a warning in each of the document load created spans like:
invalid parent span IDs=6b07cadce862131f; skipping clock skew adjustment

[Flarna]

I guess you have to overwrite also the traceId of all spans to the traceId of your root span.

[kristijanstefanoski]

The only problem I saw with this approach is that now whenever HTTP request shows in Jaeger it does not automatically connect it with my backend service, I guess this is because traceheader parent is different than the traceId and parentSpanId I set? Any way around that?

[Flarna]

You asked for setting a single parent for all spans and now you ask for correctly linking with the actual http request. That's not possible because a span can have only one parent.
You could try to utilize span links.

It seems you try to use OpenTelemetry in a way it is not built for. Therefore I guess whatever problem you "solve" by e.g. rewriting captured data will open at least one new problem.

Instead of postprocessing the data I recommend to start the spans in the order/at the places you want. if the existing instrumentations don't fit then don't use them instead create what fits you use case. Or if it makes sense enhance them to support your use case.

[kristijanstefanoski]

No, what I meant is - everything should be under a single parent but the HTTP request from the frontend should be linked with the reported one from the backend. This is how it was working before I did the linking with a 'root' span

[kristijanstefanoski]

For example what I see currently as a result:

• Root Span
  • Click (User interaction)
    - HTTP GET

And this is where it stops, previously I had:
- Click (User interaction)
- HTTP GET
- Backend Middleware etc...

I suppose this is happening because in my CustomExporter I change the parentSpanId and traceId but what I see reach my server is a request with a traceparent header that does not match the parentSpanId and traceId that I set...

[Flarna]

You rewrite the span at export time - when they are already ended. Before they are ended they use the correct traceId/spanId and that one is also propagated and seen by your backend.

As stated above instead of rewriting span data you should create/nest spans correct from beginning.