Optimize the shadowsocks server on Linux
First of all, upgrade your Linux kernel to 3.5 or later.
Step 1, increase the maximum number of open file descriptors
To handle thousands of concurrent TCP connections, we should increase the limit of file descriptors opened.
Add these two lines
* soft nofile 51200
* hard nofile 51200
Then, before you start the shadowsocks server, set the ulimit first
ulimit -n 51200
Step 2, Tune the kernel parameters
The priciples of tuning parameters for shadowsocks are
- Reuse ports and conections as soon as possible.
- Enlarge the queues and buffers as large as possible.
- Choose the TCP congestion algorithm for large latency and high throughput.
Here is an example
/etc/sysctl.conf of our production servers:
fs.file-max = 51200
net.core.rmem_max = 67108864
net.core.wmem_max = 67108864
net.core.netdev_max_backlog = 250000
net.core.somaxconn = 4096
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_tw_recycle = 0
net.ipv4.tcp_fin_timeout = 30
net.ipv4.tcp_keepalive_time = 1200
net.ipv4.ip_local_port_range = 10000 65000
net.ipv4.tcp_max_syn_backlog = 8192
net.ipv4.tcp_max_tw_buckets = 5000
net.ipv4.tcp_fastopen = 3
net.ipv4.tcp_mem = 25600 51200 102400
net.ipv4.tcp_rmem = 4096 87380 67108864
net.ipv4.tcp_wmem = 4096 65536 67108864
net.ipv4.tcp_mtu_probing = 1
net.ipv4.tcp_congestion_control = hybla
Of course, remember to execute
sysctl -p to reload the config at runtime.
How to verify your optimizations work
Use munin or any server monitor tools to generate the graph of your TCP connections. A well tuned server should look like this