Observability/metrics update (#1962)

* Removing logging from the NOOP implementatino

* Simplifying the percentiles option

* Simple logging implementation

Co-authored-by: chris <chris@Profanity.local>

metrics/prometheus/metric_family.go

@@ -19,13 +19,22 @@ type metricFamily struct {
 
 // newMetricFamily returns a new metricFamily (useful in case we want to change the structure later):
 func (r *Reporter) newMetricFamily() metricFamily {
+
+	// Take quantile thresholds from our pre-defined list:
+	timingObjectives := make(map[float64]float64)
+	for _, percentile := range r.options.Percentiles {
+		if quantileThreshold, ok := quantileThresholds[percentile]; ok {
+			timingObjectives[percentile] = quantileThreshold
+		}
+	}
+
 	return metricFamily{
 		counters:           make(map[string]*prometheus.CounterVec),
 		gauges:             make(map[string]*prometheus.GaugeVec),
 		timings:            make(map[string]*prometheus.SummaryVec),
 		defaultLabels:      r.convertTags(r.options.DefaultTags),
 		prometheusRegistry: r.prometheusRegistry,
-		timingObjectives:   r.options.TimingObjectives,
+		timingObjectives:   timingObjectives,
 	}
 }
 

metrics/prometheus/reporter.go

@@ -10,6 +10,12 @@ import (
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
+var (
+	// quantileThresholds maps quantiles / percentiles to error thresholds (required by the Prometheus client).
+	// Must be from our pre-defined set [0.0, 0.5, 0.75, 0.90, 0.95, 0.98, 0.99, 1]:
+	quantileThresholds = map[float64]float64{0.0: 0, 0.5: 0.05, 0.75: 0.04, 0.90: 0.03, 0.95: 0.02, 0.98: 0.001, 1: 0}
+)
+
 // Reporter is an implementation of metrics.Reporter:
 type Reporter struct {
 	options            metrics.Options