Rackspace currently runs Swift on Ubuntu Server 10.04, and the following changes have been found to be useful for our use cases.
The following settings should be in /etc/sysctl.conf:
# disable TIME_WAIT.. wait..
net.ipv4.tcp_tw_recycle=1
net.ipv4.tcp_tw_reuse=1
# disable syn cookies
net.ipv4.tcp_syncookies = 0
# double amount of allowed conntrack
net.ipv4.netfilter.ip_conntrack_max = 262144
To load the updated sysctl settings, run sudo sysctl -p
A note about changing the TIME_WAIT values. By default the OS will hold a port open for 60 seconds to ensure that any remaining packets can be received. During high usage, and with the number of connections that are created, it is easy to run out of ports. We can change this since we are in control of the network. If you are not in control of the network, or do not expect high loads, then you may not want to adjust those values.
