How do hosters organize shared hosting?

Question

Virtualization

How do hosters technically limit owners of sites on shared hosting at the moment?
If we take standard shared hosting , nginx + apache\php-fpm + mysql
RAM , HDD , throughput?

Any kind of virtualization (KVM\openvz) for a certain number of sites + something like LXC\DOcker (for each)?
Or just monitoring and chopping in case of violation of the quota?

UPD1:
I took a dedicated server, made an openvz container for my tasks and a couple more for friends.
So I want to make a common container out of the remaining resources, dump other projects there, but how to isolate them as much as possible so that the entire container is not overloaded due to any of the projects.

Answer 1

I just recently wanted to organize hosting.
I took a server, installed VMmanager KVM there.
Created 2 virtual machines (Billmanager 5, ISPmanager 5)
There you can configure the tariffs: how much disk, RAM, domains, mailboxes, traffic, etc.
I think it's better to do it on KVM. I recommend to take the server on the SSD

Answer 2

If shared hosting - then by the number of Apache (or PHP) processes, by the amount of RAM consumed per PHP process (from 64 to 400 MB in total per user - depending on the hosting), by the amount of traffic.
In case of exceeding the indicated norms, the client is warned (usually). Sometimes when the limits are exceeded, they block, and for some amount they offer to remove the blocking.
If you have a site with heavy scripts - better focus on VPS - there you are your own administrator.