private void Handle(ClusterActorDiscoveryMessage.ClusterActorUp m)
        {
            _log.Debug($"ClusterActorUp: Actor={m.Actor.Path} Tag={m.Tag}");

            NodeItem node;

            if (_nodeMap.TryGetValue(Sender, out node) == false)
            {
                _log.Error($"Cannot find node: Discovery={Sender.Path}");
                return;
            }

            node.ActorItems.Add(new ActorItem {
                Actor = m.Actor, Tag = m.Tag
            });

            NotifyActorUpToMonitor(m.Actor, m.Tag);
        }