@Override
    public int hashCode() {
        return Objects.hash(cluster, index, retired, stringValue);
    }
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