[#1680] replicator: Consider nodes under maintenance as OK

Nodes under maintenance SHOULD not respond to object requests. Based on
this, storage node's Policer SHOULD consider such nodes as problem ones.
However, to prevent spam with the new replicas, on the contrary, Policer
should consider them normal.

Make `Policer.processNodes` to exclude elements if `IsMaintenance()`
with shortage decreasing.

Signed-off-by: Leonard Lyubich <ctulhurider@gmail.com>

pkg/services/policer/check.go

@@ -2,6 +2,7 @@ package policer
 
 import (
 	"context"
+	"encoding/hex"
 
 	"github.com/nspcc-dev/neofs-node/pkg/core/container"
 	"github.com/nspcc-dev/neofs-node/pkg/local_object_storage/engine"
@@ -142,6 +143,18 @@ func (p *Policer) processNodes(ctx *processPlacementContext, addr oid.Address,
 	nodes []netmap.NodeInfo, shortage uint32, checkedNodes *nodeCache) {
 	prm := new(headsvc.RemoteHeadPrm).WithObjectAddress(addr)
 
+	handleMaintenance := func(node netmap.NodeInfo) {
+		// consider remote nodes under maintenance as problem OK. Such
+		// nodes MAY not respond with object, however, this is how we
+		// prevent spam with new replicas.
+		checkedNodes.submitReplicaHolder(node)
+		shortage--
+
+		p.log.Debug("consider node under maintenance as OK",
+			zap.String("node", hex.EncodeToString(node.PublicKey())),
+		)
+	}
+
 	for i := 0; shortage > 0 && i < len(nodes); i++ {
 		select {
 		case <-ctx.Done():
@@ -153,6 +166,8 @@ func (p *Policer) processNodes(ctx *processPlacementContext, addr oid.Address,
 			ctx.needLocalCopy = true
 
 			shortage--
+		} else if nodes[i].IsMaintenance() {
+			handleMaintenance(nodes[i])
 		} else {
 			if status := checkedNodes.processStatus(nodes[i]); status >= 0 {
 				if status == 0 {