feat: add status code label to docs metric

If a request fails record the status code with the elasticsearch.events.processed
metric.
Improve debugging and analysis of failed requests

appender.go

@@ -35,6 +35,7 @@ import (
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/codes"
 	"go.opentelemetry.io/otel/metric"
+	semconv "go.opentelemetry.io/otel/semconv/v1.26.0"
 	"go.opentelemetry.io/otel/trace"
 	"go.uber.org/zap"
 	"golang.org/x/sync/errgroup"
@@ -397,7 +398,7 @@ func (a *Appender) flush(ctx context.Context, bulkIndexer *BulkIndexer) error {
 			}
 			if status != "" {
 				a.addCount(int64(n), legacy, a.metrics.docsIndexed,
-					metric.WithAttributes(attribute.String("status", status)),
+					metric.WithAttributes(attribute.String("status", status), semconv.HTTPResponseStatusCode(errFailed.statusCode)),
 				)
 			}
 		}

appender_test.go

@@ -45,6 +45,7 @@ import (
 	"go.opentelemetry.io/otel/sdk/metric/metricdata/metricdatatest"
 	sdktrace "go.opentelemetry.io/otel/sdk/trace"
 	"go.opentelemetry.io/otel/sdk/trace/tracetest"
+	semconv "go.opentelemetry.io/otel/semconv/v1.26.0"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
 	"go.uber.org/zap/zaptest/observer"
@@ -693,7 +694,17 @@ func TestAppenderFlushRequestError(t *testing.T) {
 			w.WriteHeader(sc)
 			w.Write([]byte(`{"error": {"root_cause": [{"type": "x_content_parse_exception","reason": "reason"}],"type": "x_content_parse_exception","reason": "reason","caused_by": {"type": "json_parse_exception","reason": "reason"}},"status": 400}`))
 		})
-		indexer, err := docappender.New(client, docappender.Config{FlushInterval: time.Minute})
+
+		rdr := sdkmetric.NewManualReader(sdkmetric.WithTemporalitySelector(
+			func(ik sdkmetric.InstrumentKind) metricdata.Temporality {
+				return metricdata.DeltaTemporality
+			},
+		))
+
+		indexer, err := docappender.New(client, docappender.Config{
+			FlushInterval: time.Minute,
+			MeterProvider: sdkmetric.NewMeterProvider(sdkmetric.WithReader(rdr)),
+		})
 		require.NoError(t, err)
 		defer indexer.Close(context.Background())
 
@@ -716,15 +727,33 @@ func TestAppenderFlushRequestError(t *testing.T) {
 			BytesTotal:             bytesTotal,
 			BytesUncompressedTotal: bytesUncompressedTotal,
 		}
+		var status string
 		switch {
 		case sc == 429:
+			status = "TooMany"
 			wantStats.TooManyRequests = int64(docs)
 		case sc >= 500:
+			status = "FailedServer"
 			wantStats.FailedServer = int64(docs)
 		case sc >= 400 && sc != 429:
+			status = "FailedClient"
 			wantStats.FailedClient = int64(docs)
 		}
 		assert.Equal(t, wantStats, stats)
+
+		var rm metricdata.ResourceMetrics
+		assert.NoError(t, rdr.Collect(context.Background(), &rm))
+
+		var asserted atomic.Int64
+		assertCounter := docappendertest.NewAssertCounter(t, &asserted)
+		docappendertest.AssertOTelMetrics(t, rm.ScopeMetrics[0].Metrics, func(m metricdata.Metrics) {
+			switch m.Name {
+			case "elasticsearch.events.processed":
+				assertCounter(m, 3, attribute.NewSet(attribute.String("status", status), semconv.HTTPResponseStatusCode(sc)))
+			}
+		})
+		assert.Equal(t, int64(1), asserted.Load())
+
 	}
 	t.Run("400", func(t *testing.T) {
 		test(t, http.StatusBadRequest, "flush failed (400): {\"error\":{\"type\":\"x_content_parse_exception\",\"caused_by\":{\"type\":\"json_parse_exception\"}}}")