Fix cluster bucket stats API for prometheus (#11970)

Metrics calculation was accumulating inital usage across all nodes
rather than using initial usage only once.

Also fixing:
- bug where all  peer traffic was going to the same node.
- reset counters when replication status changes from
PENDING -> FAILED

cmd/bucket-replication-stats.go

@@ -37,6 +37,7 @@ func (b *BucketReplicationStats) hasReplicationUsage() bool {
 type ReplicationStats struct {
 	sync.RWMutex
 	Cache      map[string]*BucketReplicationStats
+	UsageCache map[string]*BucketReplicationStats // initial usage
 }
 
 // Delete deletes in-memory replication statistics for a bucket.
@@ -48,6 +49,8 @@ func (r *ReplicationStats) Delete(bucket string) {
 	r.Lock()
 	defer r.Unlock()
 	delete(r.Cache, bucket)
+	delete(r.UsageCache, bucket)
+
 }
 
 // Update updates in-memory replication statistics with new values.
@@ -62,7 +65,6 @@ func (r *ReplicationStats) Update(bucket string, n int64, status, prevStatus rep
 		b = &BucketReplicationStats{}
 	}
 	r.RUnlock()
-
 	switch status {
 	case replication.Pending:
 		if opType == replication.ObjectReplicationType {
@@ -87,10 +89,15 @@ func (r *ReplicationStats) Update(bucket string, n int64, status, prevStatus rep
 		}
 	case replication.Failed:
 		// count failures only once - not on every retry
+		switch prevStatus { // adjust counters based on previous state
+		case replication.Pending:
+			atomic.AddUint64(&b.PendingCount, ^uint64(0))
+		}
 		if opType == replication.ObjectReplicationType {
 			if prevStatus == replication.Pending {
 				atomic.AddUint64(&b.FailedSize, uint64(n))
 				atomic.AddUint64(&b.FailedCount, 1)
+				atomic.AddUint64(&b.PendingSize, ^uint64(n-1))
 			}
 		}
 	case replication.Replica:
@@ -98,6 +105,32 @@ func (r *ReplicationStats) Update(bucket string, n int64, status, prevStatus rep
 			atomic.AddUint64(&b.ReplicaSize, uint64(n))
 		}
 	}
+	r.Lock()
+	r.Cache[bucket] = b
+	r.Unlock()
+}
+
+// GetInitialUsage gets initial usage from the time of cluster initialization
+func (r *ReplicationStats) GetInitialUsage(bucket string) BucketReplicationStats {
+	if r == nil {
+		return BucketReplicationStats{}
+	}
+
+	r.RLock()
+	defer r.RUnlock()
+
+	st, ok := r.UsageCache[bucket]
+	if !ok {
+		return BucketReplicationStats{}
+	}
+	return BucketReplicationStats{
+		PendingSize:    atomic.LoadUint64(&st.PendingSize),
+		FailedSize:     atomic.LoadUint64(&st.FailedSize),
+		ReplicatedSize: atomic.LoadUint64(&st.ReplicatedSize),
+		ReplicaSize:    atomic.LoadUint64(&st.ReplicaSize),
+		PendingCount:   atomic.LoadUint64(&st.PendingCount),
+		FailedCount:    atomic.LoadUint64(&st.FailedCount),
+	}
 }
 
 // Get total bytes pending replication for a bucket
@@ -128,6 +161,7 @@ func (r *ReplicationStats) Get(bucket string) BucketReplicationStats {
 func NewReplicationStats(ctx context.Context, objectAPI ObjectLayer) *ReplicationStats {
 	st := &ReplicationStats{
 		Cache:      make(map[string]*BucketReplicationStats),
+		UsageCache: make(map[string]*BucketReplicationStats),
 	}
 
 	dataUsageInfo, err := loadDataUsageFromBackend(ctx, objectAPI)
@@ -150,7 +184,7 @@ func NewReplicationStats(ctx context.Context, objectAPI ObjectLayer) *Replicatio
 			FailedCount:    usage.ReplicationFailedCount,
 		}
 		if b.hasReplicationUsage() {
-			st.Cache[bucket] = b
+			st.UsageCache[bucket] = b
 		}
 	}
 

cmd/metrics.go

@@ -444,9 +444,16 @@ func getLatestReplicationStats(bucket string, u madmin.BucketUsageInfo) (s Bucke
 		replStats.ReplicaSize += bucketStat.ReplicationStats.ReplicaSize
 		replStats.ReplicatedSize += bucketStat.ReplicationStats.ReplicatedSize
 	}
+	usageStat := globalReplicationStats.GetInitialUsage(bucket)
+	replStats.FailedCount += usageStat.FailedCount
+	replStats.FailedSize += usageStat.FailedSize
+	replStats.PendingCount += usageStat.PendingCount
+	replStats.PendingSize += usageStat.PendingSize
+	replStats.ReplicaSize += usageStat.ReplicaSize
+	replStats.ReplicatedSize += usageStat.ReplicatedSize
 
 	// use in memory replication stats if it is ahead of usage info.
-	if replStats.ReplicatedSize > u.ReplicatedSize {
+	if replStats.ReplicatedSize >= u.ReplicatedSize {
 		s.ReplicatedSize = replStats.ReplicatedSize
 	} else {
 		s.ReplicatedSize = u.ReplicatedSize

cmd/notification.go

@@ -704,6 +704,7 @@ func (sys *NotificationSys) GetClusterBucketStats(ctx context.Context, bucketNam
 	bucketStats := make([]BucketStats, len(sys.peerClients))
 	for index, client := range sys.peerClients {
 		index := index
+		client := client
 		ng.Go(ctx, func() error {
 			if client == nil {
 				return errPeerNotReachable