/etc/sysctl.conf

В Интернете довольно много разных примеров конфигурации ядра Linux для поддержания большого количества соединений, высоконагруженных веб проектов и противодействия DDoS-атакам. Вот ещё один из примеров, что я уже смог попробовать на практике. Скажу сразу — мне более чем помогло. Попробуйте и вы.
/etc/sysctl.conf

# sysctl settings are defined through files in
# /usr/lib/sysctl.d/, /run/sysctl.d/, and /etc/sysctl.d/.
#
# Vendors settings live in /usr/lib/sysctl.d/.
# To override a whole file, create a new file with the same in
# /etc/sysctl.d/ and put new settings there. To override
# only specific settings, add a file with a lexically later
# name in /etc/sysctl.d/ and put new settings there.
#
# For more information, see sysctl.conf(5) and sysctl.d(5).

net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.all.send_redirects = 0
net.ipv4.tcp_max_orphans = 65536
net.ipv4.tcp_fin_timeout = 10
net.ipv4.tcp_keepalive_time = 1800
net.ipv4.tcp_keepalive_intvl = 15
net.ipv4.tcp_keepalive_probes = 5
net.ipv4.tcp_max_syn_backlog = 4096
net.ipv4.tcp_synack_retries = 1
net.ipv4.tcp_mem = 50576   64768   98152
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216
net.ipv4.tcp_orphan_retries = 0
net.ipv4.tcp_syncookies = 0
net.ipv4.netfilter.ip_conntrack_max = 16777216
net.netfilter.nf_conntrack_max = 16777216
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_sack = 1
net.ipv4.tcp_congestion_control = htcp
net.ipv4.tcp_no_metrics_save = 1
net.ipv4.route.flush = 1
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.lo.rp_filter = 1
net.ipv4.conf.eth0.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.lo.accept_source_route = 0
net.ipv4.conf.eth0.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.ip_local_port_range = 1024 65535
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_rfc1337 = 1
net.ipv4.ip_forward = 0
net.ipv4.icmp_echo_ignore_broadcasts = 1
net.ipv4.icmp_echo_ignore_all = 1
net.ipv4.icmp_ignore_bogus_error_responses = 1
net.core.somaxconn = 65535
net.core.netdev_max_backlog = 1000
net.core.rmem_default = 65536
net.core.wmem_default = 65536
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
fs.inotify.max_user_watches = 16777216