haproxy
logs
sudo tail -f /var/log/haproxy*.log
example error in log
217.149.135.12:61196 [18/Mar/2015:14:22:43.421] https~ nodeapp/nodeapp2 23/0/0/-1/23 -1 0 - - SD-- 24/24/24/2/0 0/0 "GET /socket.io/?key=54eafcd19008aa8312369eb4NJifImPah56lwJcxPqek&EIO=3&transport=polling&t=1426684963873-4 HTTP/1.1"