public void shutdown() {
        messageResponder.interrupt();
        try{ messageResponder.join(); } catch (InterruptedException e) { /* ignore */ }
        disconnect();
    }
History of received cluster states.
Any access to this list or to its members must be synchronized on the timer variable.
clustercontroller-core/src/test/java/com/yahoo/vespa/clustercontroller/core/DummyVdsNode.java