Servers arhitecture with docker SWARM
We need to host multiple sites on multiple servers in same datacenter. Containers will comunicate to eachother via private ip( please take a closer look at open ports - between containers, we need to close ports on back-end servers).
We need memory and processor share-ing between containers(cgroups v2 -(cant post the link here)
First will need to use CSF(this won't be in docker)+ loadbalancer/s (haproxy) (1 or 2)+ server cache(nginx) + webservers 2 or 3(nginx)+ php-fpm(latest)+ loadbalancer(haproxy for databases)+ redis(for caching databases requests)+ mariadb galera cluser or clusters + monitoring.
We don't know if above setup is correct, we can talk it over. Basically we need nginx with pagespeed module and with certbot (let's encrypt)+ php-fpm latest+ galera cluser. The others we can consult on it.
Basically we need to place as many sites as we want in this setup and if we need more power just rent another server and install docker with needed container. If a harddisk crashes we need site/s to be online until hosting will replace the the faulty hdd.