In cluster mode prefer node with slots in 2 masters case

internal/app/master.go

@@ -54,6 +54,22 @@ func (app *App) getMasterHost(shardState map[string]*HostState) (string, error)
 		}
 	}
 	if len(masters) > 1 {
+		if app.mode == modeCluster {
+			mastersWithSlots := make([]string, 0)
+			for _, master := range masters {
+				node := app.shard.Get(master)
+				hasSlots, err := node.HasClusterSlots(app.ctx)
+				if err != nil {
+					return "", fmt.Errorf("unable to check slots on %s", master)
+				}
+				if hasSlots {
+					mastersWithSlots = append(mastersWithSlots, master)
+				}
+			}
+			if len(mastersWithSlots) == 1 {
+				return mastersWithSlots[0], nil
+			}
+		}
 		return "", fmt.Errorf("got more than 1 master: %s", masters)
 	}
 	if len(masters) == 0 {

internal/redis/node.go

@@ -542,3 +542,23 @@ func (n *Node) ClusterMeet(ctx context.Context, addr string, port, clusterBusPor
 	cmd := n.conn.Do(ctx, n.config.Renames.Cluster, n.config.Renames.ClusterMeet, addr, strconv.Itoa(port), strconv.Itoa(clusterBusPort))
 	return cmd.Err()
 }
+
+// HasClusterSlots checks if node has any slot assigned
+func (n *Node) HasClusterSlots(ctx context.Context) (bool, error) {
+	cmd := n.conn.ClusterNodes(ctx)
+	err := cmd.Err()
+	if err != nil {
+		return false, err
+	}
+	lines := strings.Split(cmd.Val(), "\n")
+	for _, line := range lines {
+		splitted := strings.Split(line, " ")
+		if len(splitted) < 3 {
+			continue
+		}
+		if strings.Contains(splitted[2], "myself") {
+			return len(splitted) > 8, nil
+		}
+	}
+	return false, nil
+}