ddtrace/tracer: report number of instrumentations used as health metric

ddtrace/tracer/tracer.go

@@ -8,6 +8,7 @@ package tracer
 import (
 	gocontext "context"
 	"encoding/binary"
+	"fmt"
 	"log/slog"
 	"math"
 	"os"
@@ -347,6 +348,17 @@ func newTracer(opts ...StartOption) *tracer {
 		t.abandonedSpansDebugger = newAbandonedSpansDebugger()
 		t.abandonedSpansDebugger.Start(t.config.spanTimeout)
 	}
+	for name, conf := range c.integrations {
+		if !conf.Instrumented {
+			continue
+		}
+		v := conf.Version
+		if v == "" {
+			v = "unknown"
+		}
+		t.statsd.Incr("datadog.tracer.instrumentations", []string{fmt.Sprintf("instrumentation:%s", name), fmt.Sprintf("instrumentation_version:%s", v)}, 1)
+	}
+
 	t.wg.Add(1)
 	go func() {
 		defer t.wg.Done()

ddtrace/tracer/tracer_test.go

@@ -255,6 +255,34 @@ func TestTracerStart(t *testing.T) {
 		tr.Stop()
 		tr.Stop()
 	})
+
+	t.Run("integration_health_metric", func(t *testing.T) {
+		assert := assert.New(t)
+		defer clearIntegrationsForTests()
+		var tg statsdtest.TestStatsdClient
+
+		ok := MarkIntegrationImported("github.com/go-chi/chi")
+		assert.True(ok)
+		tr, _, _, stop := startTestTracer(t, withStatsdClient(&tg))
+		defer stop()
+
+		tg.Wait(assert, 1, 100*time.Millisecond)
+
+		conf, ok := tr.config.integrations["chi"]
+		assert.True(ok)
+		assert.True(conf.Instrumented)
+
+		counts := tg.Counts()
+		assert.Equal(int64(1), counts["datadog.tracer.instrumentations"])
+
+		calls := tg.IncrCalls()
+		for _, c := range statsdtest.FilterCallsByName(calls, "datadog.tracer.instrumentations") {
+			assert.EqualValues(c.GetTags(), []string{"instrumentation:chi", "instrumentation_version:unknown"})
+			return
+		}
+		assert.Fail("expected instrumentation to have appropriate tags")
+
+	})
 }
 
 func TestTracerLogFile(t *testing.T) {

internal/statsdtest/statsdtest.go

@@ -55,6 +55,10 @@ func (tg *TestStatsdClient) addCount(name string, value int64) {
 	tg.counts[name] += value
 }
 
+func (tc *TestStatsdCall) GetTags() []string {
+	return tc.tags
+}
+
 func (tg *TestStatsdClient) Gauge(name string, value float64, tags []string, rate float64) error {
 	return tg.addMetric(callTypeGauge, tags, TestStatsdCall{
 		name:     name,
@@ -214,6 +218,16 @@ func (tg *TestStatsdClient) CallsByName() map[string]int {
 	return counts
 }
 
+func FilterCallsByName(calls []TestStatsdCall, name string) []TestStatsdCall {
+	var matches []TestStatsdCall
+	for _, c := range calls {
+		if c.name == name {
+			matches = append(matches, c)
+		}
+	}
+	return matches
+}
+
 func (tg *TestStatsdClient) Counts() map[string]int64 {
 	tg.mu.RLock()
 	defer tg.mu.RUnlock()