Recently I learned from Marco about /etc/sysctl.d, a folder where you can drop in files instead of changing /etc/sysctl.conf directly. That gave me the idea of building a puppet module for sysctl:

https://github.com/cosimo/puppet-modules/blob/master/sysctl/README

The idea is to assemble a collection of useful sysctl snippets. I started with the usual things we use everywhere:

• LVS Direct Routing

  # LVS directives for Direct Routing
  # http://www.linuxvirtualserver.org/VS-DRouting.html
  net.ipv4.conf.lo.arp_ignore = 1
  net.ipv4.conf.lo.arp_announce = 2
  net.ipv4.conf.all.arp_ignore = 1
  net.ipv4.conf.all.arp_announce = 2
  

• TCP performance tuning

  #---------------------------------------------------------------------
  # TCP/IP performance optimization settings compared to debian defaults
  #
  # from http://varnish.projects.linpro.no/wiki/Performance
  #---------------------------------------------------------------------
  
  #net.ipv4.ip_local_port_range = 32768 61000
  net.ipv4.ip_local_port_range = 1024 65536
  # net.core.rmem_max = 131071
  net.core.rmem_max = 16777216
  # net.core.wmem_max = 131071
  net.core.wmem_max = 16777216
  # net.ipv4.tcp_rmem = 4096 87380 4194304
  net.ipv4.tcp_rmem = 4096 87380 16777216
  # net.ipv4.tcp_wmem = 4096 16384 4194304
  net.ipv4.tcp_wmem = 4096 65536 16777216
  # net.ipv4.tcp_fin_timeout = 60
  net.ipv4.tcp_fin_timeout = 20
  # net.core.netdev_max_backlog = 1000
  net.core.netdev_max_backlog = 30000
  # net.ipv4.tcp_no_metrics_save = 0
  net.ipv4.tcp_no_metrics_save = 1
  # net.core.somaxconn = 128
  net.core.somaxconn = 262144
  # net.ipv4.tcp_syncookies = 0
  net.ipv4.tcp_syncookies = 1
  # net.ipv4.tcp_max_orphans = 65536
  net.ipv4.tcp_max_orphans = 262144
  # net.ipv4.tcp_max_syn_backlog = 1024
  net.ipv4.tcp_max_syn_backlog = 262144
  # net.ipv4.tcp_synack_retries = 5
  net.ipv4.tcp_synack_retries = 3
  # net.ipv4.tcp_syn_retries = 5
  net.ipv4.tcp_syn_retries = 3
  

I'm interested in both baseline settings to be applied by default everywhere (ex. vm.swappiness = <n>), and special-purpose settings to be "attached" to server roles, like db, file servers, http servers, etc… I'd love to hear from you.