docs(batcher): incorrect metricDescriptor field labels

[legendecas]

The doc says that custom batcher can determine aggregator for metrics by metricDescriptor.labels, while this is not true -- there are no metricDescriptor.labels in MetricDescriptor.

export class CustomBatcher extends UngroupedBatcher {
  aggregatorFor (metricDescriptor: MetricDescriptor) {
    if (metricDescriptor.labels === 'metricToBeAveraged') { // <= here is the problem
      return new AverageAggregator(10);
    }
    // this is exactly what the "UngroupedBatcher" does, we will re-use it
    // to fallback on the default behavior
    switch (metricDescriptor.metricKind) {
      case MetricKind.COUNTER:
        return new CounterSumAggregator();
      case MetricKind.OBSERVER:
        return new ObserverAggregator();
      default:
        return new MeasureExactAggregator();
    }
  }
}

Link: https://github.com/open-telemetry/opentelemetry-js/blob/master/doc/batcher-api.md

Also, I'd believe it can be documented too that how do we declare a metrics that will be aggregated by the custom aggregators with custom batcher.

[dyladan]

@legendecas are you planning on fixing this? If so, assign yourself please. If not, can you mark it as up-for-grabs?

[vmarchaud]

I think it was a typo when i wrote this, it's indeed not possible. At the bottom with the complete version i use if (metricDescriptor.name === 'requests').

Also, I'd believe it can be documented too that how do we declare a metrics that will be aggregated by the custom aggregators with custom batcher.

I believe thats what i was achieving with the complete exemple at the bottom ? Was i wrong ?

[legendecas]

@vmarchaud I believe thats what i was achieving with the complete exemple at the bottom

Yeah, you are right. I've missed that.