public void markServerDown(Server server) {
        if (server == null || !server.isAlive()) {
            return;
        }

        logger.error("LoadBalancer [{}]:  markServerDown called on [{}]", name, server.getId());
        server.setAlive(false);
        // forceQuickPing();

        notifyServerStatusChangeListener(singleton(server));
    }
Class that contains the mechanism to "ping" all the instances

@author stonse
ribbon-loadbalancer/src/main/java/com/netflix/loadbalancer/BaseLoadBalancer.java