hubble: count ring-buffer lost events on forward reads only

The `hubble_ring_buffer` lost events metric was incremented whenever
a reader reached the ring buffer boundary. However, reaching the
boundary does not always mean events were actually lost. Hitting the
boundary in backward scans is an expected stop condition rather than
a real loss.

This commit moves the metric count from the producer (ring.getLostEvent)
to the consumer's forward-reading paths (RingReader.Next/NextFollow).
The metric is now counted only when a consumer actually catches a lost
event. Normal ring scans no longer count the metric when they expectedly
reach that boundary.

Fixes: cilium#46584

Signed-off-by: Tomoki Sugiura <tomoki-sugiura@cybozu.co.jp>

Author: chez-shanpu

pkg/hubble/container/ring.go

@@ -7,7 +7,6 @@ import (
 	"context"
 	"fmt"
 	"io"
-	"strings"
 	"sync/atomic"
 	"unsafe"
 
@@ -16,7 +15,6 @@ import (
 	flowpb "github.com/cilium/cilium/api/v1/flow"
 	v1 "github.com/cilium/cilium/pkg/hubble/api/v1"
 	"github.com/cilium/cilium/pkg/hubble/math"
-	"github.com/cilium/cilium/pkg/hubble/metrics"
 	"github.com/cilium/cilium/pkg/lock"
 	"github.com/cilium/cilium/pkg/time"
 )
@@ -217,7 +215,6 @@ func (r *Ring) OldestWrite() uint64 {
 }
 
 func getLostEvent() *v1.Event {
-	metrics.LostEvents.WithLabelValues(strings.ToLower(flowpb.LostEventSource_HUBBLE_RING_BUFFER.String())).Inc()
 	now := time.Now().UTC()
 	return &v1.Event{
 		Timestamp: &timestamppb.Timestamp{

pkg/hubble/container/ring_reader.go

@@ -5,9 +5,12 @@ package container
 
 import (
 	"context"
+	"strings"
 	"sync"
 
+	flowpb "github.com/cilium/cilium/api/v1/flow"
 	v1 "github.com/cilium/cilium/pkg/hubble/api/v1"
+	"github.com/cilium/cilium/pkg/hubble/metrics"
 	"github.com/cilium/cilium/pkg/lock"
 )
 
@@ -67,6 +70,10 @@ func (r *RingReader) Next() (*v1.Event, error) {
 		return nil, err
 	}
 	r.idx++
+	if lost, ok := e.Event.(*flowpb.LostEvent); ok && lost.Source == flowpb.LostEventSource_HUBBLE_RING_BUFFER {
+		// count hubble_ring_buffer lost events
+		metrics.LostEvents.WithLabelValues(strings.ToLower(flowpb.LostEventSource_HUBBLE_RING_BUFFER.String())).Inc()
+	}
 	return e, nil
 }
 
@@ -115,6 +122,10 @@ func (r *RingReader) NextFollow(ctx context.Context) *v1.Event {
 		// increment idx so that future calls to the ring reader will
 		// continue reading from were we stopped.
 		r.idx++
+		if lost, ok := e.Event.(*flowpb.LostEvent); ok && lost.Source == flowpb.LostEventSource_HUBBLE_RING_BUFFER {
+			// count hubble_ring_buffer lost events
+			metrics.LostEvents.WithLabelValues(strings.ToLower(flowpb.LostEventSource_HUBBLE_RING_BUFFER.String())).Inc()
+		}
 		return e
 	case <-ctx.Done():
 		return nil