map $http_x_forwarded_for  $clientRealIp {
    "" $remote_addr;
    ~^(?P<firstAddr>[0-9\.]+),?.*$  $firstAddr;
    }

    ###safe setting to limit the request number per second
    limit_req_status 599;
    limit_req_zone $clientRealIp zone=allips:70m rate=5r/s;

limit_req zone=allips burst=5 nodelay;

import threading
import time,urllib2


url = 'http://sf.gg/'
def worker():
  try:
   response = urllib2.urlopen(url)
   print response.getcode()
  except urllib2.HTTPError, e:
   print e.code

for i in range(2000):
  t = threading.Thread(target=worker)
  t.start()