We are seeing some requests taking a while before being able to get a connection through to HAProxy. Using tcpdump we are seeing cases where the clients needs 9 SYN packets before HAProxy responds to the connect. Other services on the same box do not suffer the same problem, so it's definitely HAProxy being overloaded. Is there anything we can tune to improve the situation?
Here are the network-related parts of our sysctl config: net.core.rmem_max=16777216 net.core.wmem_max=16777216 net.ipv4.tcp_rmem=4096 87380 16777216 net.ipv4.tcp_wmem=4096 65536 16777216 net.core.netdev_max_backlog=15000 net.ipv4.tcp_max_tw_buckets = 16777216 net.core.somaxconn = 262144 net.ipv4.tcp_tw_recycle = 1 net.ipv4.tcp_max_syn_backlog = 262144 HAProxy is serving about ~300 req/s on the box. The processor load is not very high (~3.3 among four cores), and we don't see any obvioius bottlenecks. However, it is running Varnish as well. HAProxy 1.3.15.7.
