public int getCongestionRatePercentage(String zone) {
        if (zone == null) {
            return 0;
        }
        zone = zone.toLowerCase();
        List<? extends Server> currentList = upServerListZoneMap.get(zone);
        if (currentList == null || currentList.size() == 0) {
            return 0;            
        }
        int serverCount = currentList.size(); 
        int activeConnectionsCount = 0;
        int circuitBreakerTrippedCount = 0;
        for (Server server: currentList) {
            ServerStats stat = getSingleServerStat(server);   
            activeConnectionsCount += stat.getActiveRequestsCount();
            if (stat.isCircuitBreakerTripped()) {
                circuitBreakerTrippedCount++;
            }
        }
        return (int) ((activeConnectionsCount + circuitBreakerTrippedCount) * 100L / serverCount); 
    }
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