The default tcp parameters of OS need to be tuned

[Sam Su]

Some of default tcp parameters of OSs are not good for the scalability of openstack, here is my suggestion:

in the file /etc/sysctl.conf
# The established connection timeout, its' default value is 432000 seconds
net.netfilter.nf_conntrack_tcp_timeout_established=600

net.ipv4.tcp_tw_recycle = 0
net.ipv4.tcp_tw_reuse = 0

# increase the kernel's internal ARP cache size
net.ipv4.neigh.default.gc_thresh1 = 1024
net.ipv4.neigh.default.gc_thresh2 = 4096
net.ipv4.neigh.default.gc_thresh3 = 8192