Add histogram exemplar support

staging/src/k8s.io/component-base/metrics/counter.go

@@ -21,6 +21,8 @@ import (
 
 	"github.com/blang/semver/v4"
 	"github.com/prometheus/client_golang/prometheus"
+	"go.opentelemetry.io/otel/trace"
+
 	dto "github.com/prometheus/client_model/go"
 )
 
@@ -40,6 +42,11 @@ var _ Metric = &Counter{}
 // All supported exemplar metric types implement the metricWithExemplar interface.
 var _ metricWithExemplar = &Counter{}
 
+// exemplarCounterMetric holds a context to extract exemplar labels from, and a counter metric to attach them to. It implements the metricWithExemplar interface.
+type exemplarCounterMetric struct {
+	*Counter
+}
+
 // NewCounter returns an object which satisfies the kubeCollector and CounterMetric interfaces.
 // However, the object returned will not measure anything unless the collector is first
 // registered, since the metric is lazily instantiated.
@@ -105,7 +112,7 @@ func (c *Counter) WithContext(ctx context.Context) CounterMetric {
 
 // withExemplar initializes the exemplarMetric object and sets the exemplar value.
 func (c *Counter) withExemplar(v float64) {
-	(&exemplarMetric{c}).withExemplar(v)
+	(&exemplarCounterMetric{c}).withExemplar(v)
 }
 
 func (c *Counter) Add(v float64) {
@@ -116,6 +123,23 @@ func (c *Counter) Inc() {
 	c.withExemplar(1)
 }
 
+// withExemplar attaches an exemplar to the metric.
+func (e *exemplarCounterMetric) withExemplar(v float64) {
+	if m, ok := e.CounterMetric.(prometheus.ExemplarAdder); ok {
+		maybeSpanCtx := trace.SpanContextFromContext(e.ctx)
+		if maybeSpanCtx.IsValid() && maybeSpanCtx.IsSampled() {
+			exemplarLabels := prometheus.Labels{
+				"trace_id": maybeSpanCtx.TraceID().String(),
+				"span_id":  maybeSpanCtx.SpanID().String(),
+			}
+			m.AddWithExemplar(v, exemplarLabels)
+			return
+		}
+	}
+
+	e.CounterMetric.Add(v)
+}
+
 // CounterVec is the internal representation of our wrapping struct around prometheus
 // counterVecs. CounterVec implements both kubeCollector and CounterVecMetric.
 type CounterVec struct {

staging/src/k8s.io/component-base/metrics/histogram.go

@@ -21,17 +21,55 @@ import (
 
 	"github.com/blang/semver/v4"
 	"github.com/prometheus/client_golang/prometheus"
+	"go.opentelemetry.io/otel/trace"
 )
 
 // Histogram is our internal representation for our wrapping struct around prometheus
 // histograms. Summary implements both kubeCollector and ObserverMetric
 type Histogram struct {
+	ctx context.Context
 	ObserverMetric
 	*HistogramOpts
 	lazyMetric
 	selfCollector
 }
 
+// exemplarHistogramMetric holds a context to extract exemplar labels from, and a historgram metric to attach them to. It implements the metricWithExemplar interface.
+type exemplarHistogramMetric struct {
+	*Histogram
+}
+
+type exemplarHistogramVec struct {
+	*HistogramVecWithContext
+	observer prometheus.Observer
+}
+
+func (h *Histogram) Observe(v float64) {
+	h.withExemplar(v)
+}
+
+// withExemplar initializes the exemplarMetric object and sets the exemplar value.
+func (h *Histogram) withExemplar(v float64) {
+	(&exemplarHistogramMetric{h}).withExemplar(v)
+}
+
+// withExemplar attaches an exemplar to the metric.
+func (e *exemplarHistogramMetric) withExemplar(v float64) {
+	if m, ok := e.Histogram.ObserverMetric.(prometheus.ExemplarObserver); ok {
+		maybeSpanCtx := trace.SpanContextFromContext(e.ctx)
+		if maybeSpanCtx.IsValid() && maybeSpanCtx.IsSampled() {
+			exemplarLabels := prometheus.Labels{
+				"trace_id": maybeSpanCtx.TraceID().String(),
+				"span_id":  maybeSpanCtx.SpanID().String(),
+			}
+			m.ObserveWithExemplar(v, exemplarLabels)
+			return
+		}
+	}
+
+	e.ObserverMetric.Observe(v)
+}
+
 // NewHistogram returns an object which is Histogram-like. However, nothing
 // will be measured until the histogram is registered somewhere.
 func NewHistogram(opts *HistogramOpts) *Histogram {
@@ -74,6 +112,7 @@ func (h *Histogram) initializeDeprecatedMetric() {
 
 // WithContext allows the normal Histogram metric to pass in context. The context is no-op now.
 func (h *Histogram) WithContext(ctx context.Context) ObserverMetric {
+	h.ctx = ctx
 	return h.ObserverMetric
 }
 
@@ -216,12 +255,37 @@ type HistogramVecWithContext struct {
 	ctx context.Context
 }
 
+func (h *exemplarHistogramVec) Observe(v float64) {
+	h.withExemplar(v)
+}
+
+func (h *exemplarHistogramVec) withExemplar(v float64) {
+	if m, ok := h.observer.(prometheus.ExemplarObserver); ok {
+		maybeSpanCtx := trace.SpanContextFromContext(h.HistogramVecWithContext.ctx)
+		if maybeSpanCtx.IsValid() && maybeSpanCtx.IsSampled() {
+			m.ObserveWithExemplar(v, prometheus.Labels{
+				"trace_id": maybeSpanCtx.TraceID().String(),
+				"span_id":  maybeSpanCtx.SpanID().String(),
+			})
+			return
+		}
+	}
+
+	h.observer.Observe(v)
+}
+
 // WithLabelValues is the wrapper of HistogramVec.WithLabelValues.
-func (vc *HistogramVecWithContext) WithLabelValues(lvs ...string) ObserverMetric {
-	return vc.HistogramVec.WithLabelValues(lvs...)
+func (vc *HistogramVecWithContext) WithLabelValues(lvs ...string) *exemplarHistogramVec {
+	return &exemplarHistogramVec{
+		HistogramVecWithContext: vc,
+		observer:                vc.HistogramVec.WithLabelValues(lvs...),
+	}
 }
 
 // With is the wrapper of HistogramVec.With.
-func (vc *HistogramVecWithContext) With(labels map[string]string) ObserverMetric {
-	return vc.HistogramVec.With(labels)
+func (vc *HistogramVecWithContext) With(labels map[string]string) *exemplarHistogramVec {
+	return &exemplarHistogramVec{
+		HistogramVecWithContext: vc,
+		observer:                vc.HistogramVec.With(labels),
+	}
 }

staging/src/k8s.io/component-base/metrics/histogram_test.go

@@ -17,12 +17,15 @@ limitations under the License.
 package metrics
 
 import (
+	"context"
 	"testing"
 
 	"github.com/blang/semver/v4"
 	"github.com/prometheus/client_golang/prometheus"
+	dto "github.com/prometheus/client_model/go"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"go.opentelemetry.io/otel/trace"
 
 	apimachineryversion "k8s.io/apimachinery/pkg/version"
 )
@@ -313,3 +316,179 @@ func TestHistogramWithLabelValueAllowList(t *testing.T) {
 		})
 	}
 }
+
+func TestHistogramWithExemplar(t *testing.T) {
+	// Arrange.
+	traceID := trace.TraceID([]byte("trace-0000-xxxxx"))
+	spanID := trace.SpanID([]byte("span-0000-xxxxx"))
+	ctxForSpanCtx := trace.ContextWithSpanContext(context.Background(), trace.NewSpanContext(trace.SpanContextConfig{
+		TraceID:    traceID,
+		SpanID:     spanID,
+		TraceFlags: trace.FlagsSampled,
+	}))
+	value := float64(10)
+
+	histogram := NewHistogram(&HistogramOpts{
+		Name:    "histogram_exemplar_test",
+		Help:    "helpless",
+		Buckets: []float64{100},
+	})
+	_ = histogram.WithContext(ctxForSpanCtx)
+
+	registry := newKubeRegistry(apimachineryversion.Info{
+		Major:      "1",
+		Minor:      "15",
+		GitVersion: "v1.15.0-alpha-1.12345",
+	})
+	registry.MustRegister(histogram)
+
+	// Act.
+	histogram.Observe(value)
+
+	// Assert.
+	mfs, err := registry.Gather()
+	if err != nil {
+		t.Fatalf("Gather failed %v", err)
+	}
+
+	if len(mfs) != 1 {
+		t.Fatalf("Got %v metric families, Want: 1 metric family", len(mfs))
+	}
+
+	mf := mfs[0]
+	var m *dto.Metric
+	switch mf.GetType() {
+	case dto.MetricType_HISTOGRAM:
+		m = mfs[0].GetMetric()[0]
+	default:
+		t.Fatalf("Got %v metric type, Want: %v metric type", mf.GetType(), dto.MetricType_COUNTER)
+	}
+
+	want := value
+	got := m.GetHistogram().GetSampleSum()
+	if got != want {
+		t.Fatalf("Got %f, wanted %f as the count", got, want)
+	}
+
+	buckets := m.GetHistogram().GetBucket()
+	if len(buckets) == 0 {
+		t.Fatalf("Got 0 buckets, wanted 1")
+	}
+
+	e := buckets[0].GetExemplar()
+	if e == nil {
+		t.Fatalf("Got nil exemplar, wanted an exemplar")
+	}
+
+	eLabels := e.GetLabel()
+	if eLabels == nil {
+		t.Fatalf("Got nil exemplar label, wanted an exemplar label")
+	}
+
+	if len(eLabels) != 2 {
+		t.Fatalf("Got %v exemplar labels, wanted 2 exemplar labels", len(eLabels))
+	}
+
+	for _, l := range eLabels {
+		switch *l.Name {
+		case "trace_id":
+			if *l.Value != traceID.String() {
+				t.Fatalf("Got %s as traceID, wanted %s", *l.Value, traceID.String())
+			}
+		case "span_id":
+			if *l.Value != spanID.String() {
+				t.Fatalf("Got %s as spanID, wanted %s", *l.Value, spanID.String())
+			}
+		default:
+			t.Fatalf("Got unexpected label %s", *l.Name)
+		}
+	}
+}
+
+func TestHistogramVecWithExemplar(t *testing.T) {
+	// Arrange.
+	traceID := trace.TraceID([]byte("trace-0000-xxxxx"))
+	spanID := trace.SpanID([]byte("span-0000-xxxxx"))
+	ctxForSpanCtx := trace.ContextWithSpanContext(context.Background(), trace.NewSpanContext(trace.SpanContextConfig{
+		TraceID:    traceID,
+		SpanID:     spanID,
+		TraceFlags: trace.FlagsSampled,
+	}))
+	value := float64(10)
+
+	histogramVec := NewHistogramVec(&HistogramOpts{
+		Name:    "histogram_exemplar_test",
+		Help:    "helpless",
+		Buckets: []float64{100},
+	}, []string{"group"})
+	h := histogramVec.WithContext(ctxForSpanCtx)
+
+	registry := newKubeRegistry(apimachineryversion.Info{
+		Major:      "1",
+		Minor:      "15",
+		GitVersion: "v1.15.0-alpha-1.12345",
+	})
+	registry.MustRegister(histogramVec)
+
+	// Act.
+	h.WithLabelValues("foo").Observe(value)
+
+	// Assert.
+	mfs, err := registry.Gather()
+	if err != nil {
+		t.Fatalf("Gather failed %v", err)
+	}
+
+	if len(mfs) != 1 {
+		t.Fatalf("Got %v metric families, Want: 1 metric family", len(mfs))
+	}
+
+	mf := mfs[0]
+	var m *dto.Metric
+	switch mf.GetType() {
+	case dto.MetricType_HISTOGRAM:
+		m = mfs[0].GetMetric()[0]
+	default:
+		t.Fatalf("Got %v metric type, Want: %v metric type", mf.GetType(), dto.MetricType_COUNTER)
+	}
+
+	want := value
+	got := m.GetHistogram().GetSampleSum()
+	if got != want {
+		t.Fatalf("Got %f, wanted %f as the count", got, want)
+	}
+
+	buckets := m.GetHistogram().GetBucket()
+	if len(buckets) == 0 {
+		t.Fatalf("Got 0 buckets, wanted 1")
+	}
+
+	e := buckets[0].GetExemplar()
+	if e == nil {
+		t.Fatalf("Got nil exemplar, wanted an exemplar")
+	}
+
+	eLabels := e.GetLabel()
+	if eLabels == nil {
+		t.Fatalf("Got nil exemplar label, wanted an exemplar label")
+	}
+
+	if len(eLabels) != 2 {
+		t.Fatalf("Got %v exemplar labels, wanted 2 exemplar labels", len(eLabels))
+	}
+
+	for _, l := range eLabels {
+		switch *l.Name {
+		case "trace_id":
+			if *l.Value != traceID.String() {
+				t.Fatalf("Got %s as traceID, wanted %s", *l.Value, traceID.String())
+			}
+		case "span_id":
+			if *l.Value != spanID.String() {
+				t.Fatalf("Got %s as spanID, wanted %s", *l.Value, spanID.String())
+			}
+		default:
+			t.Fatalf("Got unexpected label %s", *l.Name)
+		}
+	}
+}

staging/src/k8s.io/component-base/metrics/metric.go

@@ -19,8 +19,6 @@ package metrics
 import (
 	"sync"
 
-	"go.opentelemetry.io/otel/trace"
-
 	"github.com/blang/semver/v4"
 	"github.com/prometheus/client_golang/prometheus"
 	dto "github.com/prometheus/client_model/go"
@@ -217,28 +215,6 @@ type metricWithExemplar interface {
 	withExemplar(v float64)
 }
 
-// exemplarMetric is a holds a context to extract exemplar labels from, and a metric to attach them to. It implements the metricWithExemplar interface.
-type exemplarMetric struct {
-	*Counter
-}
-
-// withExemplar attaches an exemplar to the metric.
-func (e *exemplarMetric) withExemplar(v float64) {
-	if m, ok := e.CounterMetric.(prometheus.ExemplarAdder); ok {
-		maybeSpanCtx := trace.SpanContextFromContext(e.ctx)
-		if maybeSpanCtx.IsValid() && maybeSpanCtx.IsSampled() {
-			exemplarLabels := prometheus.Labels{
-				"trace_id": maybeSpanCtx.TraceID().String(),
-				"span_id":  maybeSpanCtx.SpanID().String(),
-			}
-			m.AddWithExemplar(v, exemplarLabels)
-			return
-		}
-	}
-
-	e.CounterMetric.Add(v)
-}
-
 // no-op vecs for convenience
 var noopCounterVec = &prometheus.CounterVec{}
 var noopHistogramVec = &prometheus.HistogramVec{}