public void addMonitoring(ClusterMonitor<Node> clusterMonitor) {
        for (Node node : monitoredGroups.nodes()) clusterMonitor.add(node, true);
    }
Sets the new nodes to monitor to be the new nodes, but keep any existing node instances which are equal the new ones.
container-search/src/main/java/com/yahoo/search/dispatch/searchcluster/SearchCluster.java