NodeSDK example not working properly with getSpan

[AlexRex]

So I have my tracing configured as follows in an Express server:

import * as opentelemetry from '@opentelemetry/sdk-node'
import { getNodeAutoInstrumentations } from '@opentelemetry/auto-instrumentations-node'

import { Resource } from '@opentelemetry/resources'
import { SemanticResourceAttributes } from '@opentelemetry/semantic-conventions'

export const startTracing = async () => {
  const sdk = new opentelemetry.NodeSDK({
    resource: new Resource({
      [SemanticResourceAttributes.SERVICE_NAME]: 'api',
    }),
    instrumentations: [getNodeAutoInstrumentations()]
  })


  await sdk.start()
}

Just basically following the example from the Getting Sarted guide without the tracing exporter. So far, so good.

So in a router controller, if I do:

  app
    .use('/test', (_, res) => {
      const span = otel.trace.getSpan(otel.context.active())
      console.log(span)
      res.status(200).send('ok')
    })

I expect to see some span printed into the console, but instead I only see undefined.

If instead, I configure a tracingExporter in the NodeSDK configuration, it actually works:

  const sdk = new opentelemetry.NodeSDK({
+    traceExporter: new opentelemetry.tracing.ConsoleSpanExporter(),
    resource: new Resource({
      [SemanticResourceAttributes.SERVICE_NAME]: 'api',
    }),
    instrumentations: [getNodeAutoInstrumentations()]
  })

And I don't understand why this is the correct behavior, what if I don't want to export the traces anywhere, can I get spans anyway? I found that setting a custom trace provider also does the trick:

  const sdk = new opentelemetry.NodeSDK({
    resource: new Resource({
      [SemanticResourceAttributes.SERVICE_NAME]: 'api',
    }),
    instrumentations: [getNodeAutoInstrumentations()]
  })

+  sdk.configureTracerProvider({}, new NodeTracerProvider().getActiveSpanProcessor())

But I am not sure which is the best solution for my case right now. I want to use spans to attach the tracing id to logs, so afterward when we start tracing we can link logs with traces.

[Flarna]

I guess the use case to create spans but don't export them was not seen as useful.
The simplest solution is most likely to use a NoopSpanExporter like this:

class NoopSpanExporter implements SpanExporter {
  export(spans: ReadableSpan[], resultCallback: (result: ExportResult) => void): void {
    process.nextTick(resultCallback, ExportResultCode.SUCCESS);
  }
  shutdown(): Promise<void> {
    return Promise.resolve();
  }
}