Replace BEYLA_OTEL_USE_EXPONENTIAL_HISTOGRAMS by standard environment…

… variable

docs/sources/configure/options.md

@@ -757,6 +757,17 @@ It is disabled by default to avoid cardinality explosion.
 The `buckets` object allows overriding the bucket boundaries of diverse histograms. See
 [Overriding histogram buckets](#overriding-histogram-buckets) section for more details.
 
+| YAML                    | Environment variable                                       | Type     | Default                     |
+|-------------------------|------------------------------------------------------------|----------|-----------------------------|
+| `histogram_aggregation` | `OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION` | `string` | `explicit_bucket_histogram` |
+
+Specifies the default aggregation to use for histogram instruments.
+
+Accepted values are:
+
+* `explicit_bucket_histogram` (default): use [Explicit Bucket Histogram Aggregation](https://opentelemetry.io/docs/specs/otel/metrics/sdk/#explicit-bucket-histogram-aggregation).
+* `base2_exponential_bucket_histogram`: use [Base2 Exponential Bucket Histogram Aggregation](https://opentelemetry.io/docs/specs/otel/metrics/sdk/#base2-exponential-bucket-histogram-aggregation).
+
 ### Overriding histogram buckets
 
 For both OpenTelemetry and Prometheus metrics exporters, you can override the histogram bucket
@@ -800,14 +811,14 @@ conventions recommend a different set of bucket boundaries.
 
 ### Use native histograms and exponential histograms
 
-For Prometheus [native histograms](https://prometheus.io/docs/concepts/metric_types/#histogram) are enabled if you have the `native-histograms` feature enabled.
-
-For OpenTelemetry you can use [exponential histograms](https://opentelemetry.io/docs/specs/otel/metrics/data-model/#exponentialhistogram) for the predefined histograms instead of defining the buckets manually.
-
-| YAML       | Environment variable                                                      | Type | Default |
-| ---------- | ------------------------------------------------------------------------- | ---- | ------- |
-| `use_exponential_histograms` | `BEYLA_OTEL_USE_EXPONENTIAL_HISTOGRAMS`  | `boolean` | `false` |
+For Prometheus, [native histograms](https://prometheus.io/docs/concepts/metric_types/#histogram) are enabled if you
+[enable the `native-histograms` feature in your Prometheus collector](https://prometheus.io/docs/prometheus/latest/feature_flags/#native-histograms).
 
+For OpenTelemetry you can use [exponential histograms](https://opentelemetry.io/docs/specs/otel/metrics/data-model/#exponentialhistogram)
+for the predefined histograms instead of defining the buckets manually. You need to set up the standard
+[OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION](https://opentelemetry.io/docs/specs/otel/metrics/sdk_exporters/otlp/#additional-configuration)
+environment variable. See the `histogram_aggregation` section in the [OTEL metrics exporter](#otel-metrics-exporter) section
+for more information.
 
 ## OTEL traces exporter
 

pkg/beyla/config.go

@@ -43,11 +43,12 @@ var defaultConfig = Config{
 		},
 	},
 	Metrics: otel.MetricsConfig{
-		Protocol:          otel.ProtocolUnset,
-		MetricsProtocol:   otel.ProtocolUnset,
-		Interval:          5 * time.Second,
-		Buckets:           otel.DefaultBuckets,
-		ReportersCacheLen: ReporterLRUSize,
+		Protocol:             otel.ProtocolUnset,
+		MetricsProtocol:      otel.ProtocolUnset,
+		Interval:             5 * time.Second,
+		Buckets:              otel.DefaultBuckets,
+		ReportersCacheLen:    ReporterLRUSize,
+		HistogramAggregation: otel.AggregationExplicit,
 	},
 	Traces: otel.TracesConfig{
 		Protocol:           otel.ProtocolUnset,

pkg/beyla/config_test.go

@@ -29,6 +29,7 @@ otel_metrics_export:
   endpoint: localhost:3030
   buckets:
     duration_histogram: [0, 1, 2]
+  histogram_aggregation: base2_exponential_bucket_histogram
 prometheus_export:
   buckets:
     request_size_histogram: [0, 10, 20, 22]
@@ -104,6 +105,7 @@ network:
 				DurationHistogram:    []float64{0, 1, 2},
 				RequestSizeHistogram: otel.DefaultBuckets.RequestSizeHistogram,
 			},
+			HistogramAggregation: "base2_exponential_bucket_histogram",
 		},
 		Traces: otel.TracesConfig{
 			Protocol:           otel.ProtocolUnset,

pkg/internal/export/otel/metrics.go

@@ -39,6 +39,9 @@ const (
 
 	UsualPortGRPC = "4317"
 	UsualPortHTTP = "4318"
+
+	AggregationExplicit    = "explicit_bucket_histogram"
+	AggregationExponential = "base2_exponential_bucket_histogram"
 )
 
 type MetricsConfig struct {
@@ -59,8 +62,8 @@ type MetricsConfig struct {
 	ReportTarget   bool `yaml:"report_target" env:"BEYLA_METRICS_REPORT_TARGET"`
 	ReportPeerInfo bool `yaml:"report_peer" env:"BEYLA_METRICS_REPORT_PEER"`
 
-	Buckets                  Buckets `yaml:"buckets"`
-	UseExponentialHistograms bool    `yaml:"use_exponential_histograms" env:"BEYLA_OTEL_USE_EXPONENTIAL_HISTOGRAMS"`
+	Buckets              Buckets `yaml:"buckets"`
+	HistogramAggregation string  `yaml:"histogram_aggregation" env:"OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION"`
 
 	ReportersCacheLen int `yaml:"reporters_cache_len" env:"BEYLA_METRICS_REPORT_CACHE_LEN"`
 
@@ -171,21 +174,23 @@ func newMetricsReporter(ctx context.Context, cfg *MetricsConfig, ctxInfo *global
 }
 
 func (mr *MetricsReporter) newMetricSet(service svc.ID) (*Metrics, error) {
-	mlog().Debug("creating new Metrics reporter", "service", service)
+	mlog := mlog().With("service", service)
+	mlog.Debug("creating new Metrics reporter")
+	useExponentialHistograms := isExponentialAggregation(mr.cfg, mlog)
 	resources := otelResource(service)
 	m := Metrics{
 		ctx: mr.ctx,
 		provider: metric.NewMeterProvider(
 			metric.WithResource(resources),
 			metric.WithReader(metric.NewPeriodicReader(mr.exporter,
 				metric.WithInterval(mr.cfg.Interval))),
-			metric.WithView(otelHistogramConfig(HTTPServerDuration, mr.cfg.Buckets.DurationHistogram, mr.cfg.UseExponentialHistograms)),
-			metric.WithView(otelHistogramConfig(HTTPClientDuration, mr.cfg.Buckets.DurationHistogram, mr.cfg.UseExponentialHistograms)),
-			metric.WithView(otelHistogramConfig(RPCServerDuration, mr.cfg.Buckets.DurationHistogram, mr.cfg.UseExponentialHistograms)),
-			metric.WithView(otelHistogramConfig(RPCClientDuration, mr.cfg.Buckets.DurationHistogram, mr.cfg.UseExponentialHistograms)),
-			metric.WithView(otelHistogramConfig(SQLClientDuration, mr.cfg.Buckets.DurationHistogram, mr.cfg.UseExponentialHistograms)),
-			metric.WithView(otelHistogramConfig(HTTPServerRequestSize, mr.cfg.Buckets.RequestSizeHistogram, mr.cfg.UseExponentialHistograms)),
-			metric.WithView(otelHistogramConfig(HTTPClientRequestSize, mr.cfg.Buckets.RequestSizeHistogram, mr.cfg.UseExponentialHistograms)),
+			metric.WithView(otelHistogramConfig(HTTPServerDuration, mr.cfg.Buckets.DurationHistogram, useExponentialHistograms)),
+			metric.WithView(otelHistogramConfig(HTTPClientDuration, mr.cfg.Buckets.DurationHistogram, useExponentialHistograms)),
+			metric.WithView(otelHistogramConfig(RPCServerDuration, mr.cfg.Buckets.DurationHistogram, useExponentialHistograms)),
+			metric.WithView(otelHistogramConfig(RPCClientDuration, mr.cfg.Buckets.DurationHistogram, useExponentialHistograms)),
+			metric.WithView(otelHistogramConfig(SQLClientDuration, mr.cfg.Buckets.DurationHistogram, useExponentialHistograms)),
+			metric.WithView(otelHistogramConfig(HTTPServerRequestSize, mr.cfg.Buckets.RequestSizeHistogram, useExponentialHistograms)),
+			metric.WithView(otelHistogramConfig(HTTPClientRequestSize, mr.cfg.Buckets.RequestSizeHistogram, useExponentialHistograms)),
 		),
 	}
 	// time units for HTTP and GRPC durations are in seconds, according to the OTEL specification:
@@ -224,6 +229,20 @@ func (mr *MetricsReporter) newMetricSet(service svc.ID) (*Metrics, error) {
 	return &m, nil
 }
 
+func isExponentialAggregation(mc *MetricsConfig, mlog *slog.Logger) bool {
+	switch mc.HistogramAggregation {
+	case AggregationExponential:
+		return true
+	case AggregationExplicit:
+	// do nothing
+	default:
+		mlog.Warn("invalid value for histogram aggregation. Accepted values are: "+
+			AggregationExponential+", "+AggregationExplicit+" (default). Using default",
+			"value", mc.HistogramAggregation)
+	}
+	return false
+}
+
 // TODO: restore as private
 func InstantiateMetricsExporter(ctx context.Context, cfg *MetricsConfig, log *slog.Logger) (metric.Exporter, error) {
 	var err error