public void handleZooKeeperSessionDown() {
            fleetControllerContext.log(logger, Level.FINE, () -> "Lost contact with zookeeper server");
            synchronized(monitor) {
                lostZooKeeperConnectionEvent = true;
                monitor.notifyAll();
            }
        }
Data store for the cluster controller.
The data is stored and distributed by ZooKeeper.
clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/database/DatabaseHandler.java