nri-prom histogram improvement: add _count counter by default

[jackwilsdon]

Description

The _count counter is not included in data pushed to New Relic for Prometheus histograms.

Expected Behavior

The _count counter should be included.

Steps to Reproduce

Scrape a Prometheus histogram with the infrastructure agent and nri-prometheus. Note that the _count counter is not exported to New Relic.

Additional context

The summary type already has support for _count:

infrastructure-agent/pkg/integrations/v4/dm/telemetry.go

Lines 270 to 277 in dc896c4

	metricName = metric.Name + "_count"
	countMetric, ok := p.calculate.get(metricName, metric.Attributes, value.SampleCount, metric.Time())
	if ok {
	result = append(result, countMetric)
	} else {
	telemetryLogger.WithField("name", metricName).WithField("metric-type", metric.Type).Debug(noCalculationMadeErrMsg)
	}

But it looks like the histogram type doesn't:

infrastructure-agent/pkg/integrations/v4/dm/telemetry.go

Lines 201 to 234 in dc896c4

	metricName := metric.Name + "_sum"
	sumCount, ok := ph.calculate.get(metricName, metric.Attributes, float64(*value.SampleCount), metric.Time())
	if ok {
	result = append(result, telemetry.Summary{
	Name: metricName,
	Attributes: metric.Attributes,
	Count: 1,
	Sum: sumCount.Value,
	Min: math.NaN(),
	Max: math.NaN(),
	Timestamp: metric.Time(),
	Interval: sumCount.Interval,
	})
	} else {
	telemetryLogger.WithField("name", metricName).WithField("metric-type", metric.Type).Debug(noCalculationMadeErrMsg)
	}
	metricName = metric.Name + "_bucket"
	for _, b := range value.Buckets {
	bucketAttrs := metric.CopyAttrs()
	bucketAttrs["le"] = fmt.Sprintf("%g", *b.UpperBound)
	bucketCount, ok := ph.calculate.get(
	metricName,
	bucketAttrs,
	float64(*b.CumulativeCount),
	metric.Time(),
	)
	if ok {
	result = append(result, bucketCount)
	} else {
	telemetryLogger.WithField("name", metricName).WithField("metric-type", metric.Type).Debug(noCalculationMadeErrMsg)
	}
	}

For Maintainers Only or Hero Triaging this bug

Suggested Priority (P1,P2,P3,P4,P5):
Suggested T-Shirt size (S, M, L, XL, Unknown):

[workato-integration]

https://new-relic.atlassian.net/browse/NR-288815

[josemore]

this has been added to backlog as low-priority, see #1889 (comment)