private static ClusterStatsAggregator createNewAggregator(ClusterState clusterState) {
        Set<Integer> upDistributors = getIndicesOfUpNodes(clusterState, NodeType.DISTRIBUTOR);
        Set<Integer> upStorageNodes = getIndicesOfUpNodes(clusterState, NodeType.STORAGE);
        return new ClusterStatsAggregator(upDistributors, upStorageNodes);
    }
The Cluster Controller's view of the cluster given a particular state version. Some parts of the view
are static and only depend on the state version, e.g. which nodes are UP or DOWN. These static parts
are mostly represented by the ClusterState. The dynamic parts include stats for tracking outstanding
merges before steady-state is reached.

@author hakonhall
clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/ClusterStateView.java