@Override
    public String name() { return clusterId; }
A search node on this local machine having the entire corpus, which we therefore
should prefer to dispatch directly to, or empty if there is no such local search node.
If there is one, we also maintain the VIP status of this container based on the availability
of the corpus on this local node (up + has coverage), such that this node is taken out of rotation
if it only queries this cluster when the local node cannot be used, to avoid unnecessary
cross-node network traffic.
container-search/src/main/java/com/yahoo/search/dispatch/searchcluster/SearchCluster.java