fix(server): shed overloaded group websocket fanout

server/metrics/metrics.go

@@ -209,6 +209,10 @@ var (
 		Name: "im_topic_shared_serialization_total",
 		Help: "Shared WebSocket serialization events by pod, topic kind, and result.",
 	}, []string{"pod", "kind", "result"})
+	TopicBroadcastDropTotal = prometheus.NewCounterVec(prometheus.CounterOpts{
+		Name: "im_topic_broadcast_drop_total",
+		Help: "Realtime topic broadcasts skipped by pod, topic kind, role, and reason.",
+	}, []string{"pod", "kind", "role", "reason"})
 	ClusterM2PQueueWaitDuration = prometheus.NewHistogramVec(prometheus.HistogramOpts{
 		Name:    "im_cluster_m2p_queue_wait_duration_seconds",
 		Help:    "Time a master-to-proxy response waited in the multiplex outbound queue by pod and peer.",
@@ -282,7 +286,7 @@ func init() {
 		ClusterRouteTotal, ClusterProxyResponseTotal, InternalQueueEnqueueTotal, InternalQueueDepth,
 		InternalQueueCapacity, InternalQueueCurrent, MessagePersistDuration, MessagePublishStageDuration, TopicQueueWaitDuration,
 		TopicProcessDuration, TopicBroadcastDuration, TopicBroadcastTargets, TopicSharedSerializationTotal,
-		ClusterM2PQueueWaitDuration, ClusterM2PQueueDepth, ClusterProxyQueueWaitDuration, WSReadDispatchDuration,
+		TopicBroadcastDropTotal, ClusterM2PQueueWaitDuration, ClusterM2PQueueDepth, ClusterProxyQueueWaitDuration, WSReadDispatchDuration,
 		PushDispatchQueueEnqueueTotal, PushDispatchQueueDepth, PushDispatchQueueWaitDuration,
 		PushDispatchDuration, PushRecipientCount,
 		KafkaMessagePersistTotal)
@@ -339,6 +343,10 @@ func IncTopicSharedSerialization(kind, result string) {
 	TopicSharedSerializationTotal.WithLabelValues(metricPodName(), normalizeLabel(kind), normalizeLabel(result)).Inc()
 }
 
+func IncTopicBroadcastDrop(kind, role, reason string) {
+	TopicBroadcastDropTotal.WithLabelValues(metricPodName(), normalizeLabel(kind), normalizeLabel(role), normalizeLabel(reason)).Inc()
+}
+
 func ObserveClusterM2PEnqueue(peer string, depth int) {
 	ClusterM2PQueueDepth.WithLabelValues(metricPodName(), normalizeLabel(peer)).Observe(float64(depth))
 }