static boolean allDown(List<ServiceInstance> services) {
        Map<ServiceStatus, Long> countsByStatus = services.stream().collect(groupingBy(ServiceInstance::serviceStatus, counting()));

        return countsByStatus.getOrDefault(ServiceStatus.UP, 0L) <= 0L &&
               countsByStatus.getOrDefault(ServiceStatus.DOWN, 0L) > 0L &&
               countsByStatus.getOrDefault(ServiceStatus.UNKNOWN, 0L) == 0L;
    }
Returns true if the node is considered bad: All monitored services are down.
If a node remains bad for a long time, the NodeFailer will try to fail the node.
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/maintenance/NodeHealthTracker.java