How does the creation of subdomains by buttons work?

Question

linux

For example, there is a CRM written in php. It is necessary that everyone could get their CRM on a subdomain.
As I understand it: when registering on the site, the username.crm.ru subdomain is created, the username folder on the server in which CRM is installed and the database under this folder.
Do I understand the algorithm correctly?
What technologies can be used to launch it on the button?
What to do when there are 1000 such folders and subdomains?

Answer 1

In order not to fence a bunch of databases for each subdomain, and folders with copies of the CRM backend, thereby once again loading the system. you can configure mod_rewrite in such a way that username.crm.ru is sent to site.ru/users/username, and this router is already processed by the framework.
More or less like this.

RewriteEngine On
RewriteCond %{HTTP_HOST} !^www\.site.ru
RewriteCond %{HTTP_HOST} ([^.]+)\.site.ru
RewriteRule ^(.*)$ /users/%1