@Monitor(name=PREFIX + "CircuitBreakerTrippedCount", type = DataSourceType.GAUGE)   
    public int getCircuitBreakerTrippedCount() {
        int count = 0;
        for (String zone: upServerListZoneMap.keySet()) {
            count += getCircuitBreakerTrippedCount(zone);
        }
        return count;
    }
This is the core function to get zone stats. All stats are reported to avoid
going over the list again for a different stat.

@param servers
ribbon-loadbalancer/src/main/java/com/netflix/loadbalancer/LoadBalancerStats.java