Something like this should do the job, using the connlimit module of iptables.

iptables -t filter -I INPUT -p tcp --dport 80 -j ACCEPT

iptables -t filter -I INPUT -p tcp --dport 80 -m state \
--state RELATED,ESTABLISHED -j ACCEPT

Adjust “–connlimit-above NN” to limit the maximum connections per IP that you need.

iptables -t filter -I INPUT -p tcp --syn --dport 80 -m connlimit \
--connlimit-above 10 --connlimit-mask 32 -j DROP

Adjust “–connlimit-above NNN” to the maximum total connections you want your web server to support

iptables -t filter -I INPUT -p tcp --syn --dport 80 -m connlimit \
--connlimit-above 150 -j DROP

https://old.reddit.com/r/linuxadmin/comments/c28sdl/heres_another_one_how_do_you_control_traffic_by/