public static ClusterMembership from(ClusterSpec cluster, int index) {
        return new ClusterMembership(cluster, index, false);
    }
Returns all the information in this as a string which can be used to construct the same ClusterMembership
instance using {@link #from}. This string is currently stored in ZooKeeper on running instances.
config-provisioning/src/main/java/com/yahoo/config/provision/ClusterMembership.java