Fix confusing logging when receiving gossip from unknown (#5706)

Author: ismaelhamed

src/core/Akka.Cluster/ClusterDaemon.cs

@@ -1797,11 +1797,10 @@ public void Quarantined(UniqueAddress node)
         public void ReceiveGossipStatus(GossipStatus status)
         {
             var from = status.From;
-            if (!LatestGossip.Overview.Reachability.IsReachable(SelfUniqueAddress, from))
+            if(!LatestGossip.HasMember(from))
+                _cluster.LogInfo("Ignoring received gossip status from unknown [{0}]", from);
+            else if (!LatestGossip.IsReachable(SelfUniqueAddress, from))
                 _cluster.LogInfo("Ignoring received gossip status from unreachable [{0}]", from);
-            else if (LatestGossip.Members.All(m => !m.UniqueAddress.Equals(from)))
-                _cluster.LogInfo("Cluster Node [{0}] - Ignoring received gossip status from unknown [{1}]",
-                    _cluster.SelfAddress, from);
             else
             {
                 var comparison = status.Version.CompareTo(LatestGossip.Version);
@@ -1870,14 +1869,14 @@ public ReceiveGossipType ReceiveGossip(GossipEnvelope envelope)
                     from.Address, envelope.To);
                 return ReceiveGossipType.Ignored;
             }
-            if (!localGossip.Overview.Reachability.IsReachable(SelfUniqueAddress, from))
+            if (!localGossip.HasMember(from))
             {
-                _cluster.LogInfo("Ignoring received gossip from unreachable [{0}]", from);
+                _cluster.LogInfo("Ignoring received gossip from unknown [{0}]", from);
                 return ReceiveGossipType.Ignored;
             }
-            if (localGossip.Members.All(m => !m.UniqueAddress.Equals(from)))
+            if (!localGossip.IsReachable(SelfUniqueAddress, from))
             {
-                _cluster.LogInfo("Cluster Node [{0}] - Ignoring received gossip from unknown [{1}]", _cluster.SelfAddress, from);
+                _cluster.LogInfo("Ignoring received gossip from unreachable [{0}]", from);
                 return ReceiveGossipType.Ignored;
             }
             if (remoteGossip.Members.All(m => !m.UniqueAddress.Equals(SelfUniqueAddress)))

src/core/Akka.Cluster/Gossip.cs

@@ -294,6 +294,21 @@ public bool IsSingletonCluster
             get { return _members.Count == 1; }
         }
 
+        /// <summary>
+        /// Returns `true` if <paramref name="fromAddress"/> should be able to reach <paramref name="toAddress"/> 
+        /// based on the unreachability data.
+        /// </summary>
+        /// <param name="fromAddress">TBD</param>
+        /// <param name="toAddress">TBD</param>
+        public bool IsReachable(UniqueAddress fromAddress, UniqueAddress toAddress)
+        {
+            if (!HasMember(toAddress)) 
+                return false;
+
+            // as it looks for specific unreachable entires for the node pair we don't have to filter on team
+            return Overview.Reachability.IsReachable(fromAddress, toAddress);
+        }
+
         /// <summary>
         /// TBD
         /// </summary>
@@ -415,7 +430,7 @@ public GossipOverview Copy(ImmutableHashSet<UniqueAddress> seen = null, Reachabi
         /// TBD
         /// </summary>
         public Reachability Reachability { get { return _reachability; } }
-        
+
         /// <inheritdoc/>
         public override string ToString() => $"GossipOverview(seen=[{string.Join(", ", Seen)}], reachability={Reachability})";
     }