Ubuntu server out of box is not optimized to make full use of available hardware. This means “out-of-box” setup might fail under high load.
So we need to tweak system configuration for maximum concurrancy.
Sysctl Tweaks
Open
vim /etc/sysctl.conf
Add following towards bottom
### IMPROVE SYSTEM MEMORY MANAGEMENT ### # Increase size of file handles and inode cache fs.file-max = 2097152 # Do less swapping vm.swappiness = 10 vm.dirty_ratio = 60 vm.dirty_background_ratio = 2 ### GENERAL NETWORK SECURITY OPTIONS ### # Number of times SYNACKs for passive TCP connection. net.ipv4.tcp_synack_retries = 2 # Allowed local port range net.ipv4.ip_local_port_range = 2000 65535 # Protect Against TCP Time-Wait net.ipv4.tcp_rfc1337 = 1 # Decrease the time default value for tcp_fin_timeout connection net.ipv4.tcp_fin_timeout = 15 # Decrease the time default value for connections to keep alive net.ipv4.tcp_keepalive_time = 300 net.ipv4.tcp_keepalive_probes = 5 net.ipv4.tcp_keepalive_intvl = 15 ### TUNING NETWORK PERFORMANCE ### # Default Socket Receive Buffer net.core.rmem_default = 31457280 # Maximum Socket Receive Buffer net.core.rmem_max = 12582912 # Default Socket Send Buffer net.core.wmem_default = 31457280 # Maximum Socket Send Buffer net.core.wmem_max = 12582912 # Increase number of incoming connections net.core.somaxconn = 4096 # Increase number of incoming connections backlog net.core.netdev_max_backlog = 65536 # Increase the maximum amount of option memory buffers net.core.optmem_max = 25165824 # Increase the maximum total buffer-space allocatable # This is measured in units of pages (4096 bytes) net.ipv4.tcp_mem = 65536 131072 262144 net.ipv4.udp_mem = 65536 131072 262144 # Increase the read-buffer space allocatable net.ipv4.tcp_rmem = 8192 87380 16777216 net.ipv4.udp_rmem_min = 16384 # Increase the write-buffer-space allocatable net.ipv4.tcp_wmem = 8192 65536 16777216 net.ipv4.udp_wmem_min = 16384 # Increase the tcp-time-wait buckets pool size to prevent simple DOS attacks net.ipv4.tcp_max_tw_buckets = 1440000 net.ipv4.tcp_tw_recycle = 1 net.ipv4.tcp_tw_reuse = 1
Load Changes
Run following command to load changes to sysctl.
sysctl -p
Useful Systcl Commands
Show all system parameters with their values (default or changed)
sysctl -A
Show values of parameters modified by you
sysctl -p
Show value for a single parameter parameter-name
sysctl parameter-name
Change value for a single parameter parameter-name without editing sysctl.confmanually.
sysctl -w parameter-name=parameter-value
Above command will overwrite any previous modifications to parameter-name. Also, you may need to surround parameter-value with quotes.
Credits
We do not have expertise to tweak linux at such level. So following links helped. They differ from most configs as they offered some explanation about parameters which helped us understand what we are picking and why!
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