How to properly set up a project with a load balancer, place one database on 2 servers, place one site on 5 servers?

Question

Highload

Good afternoon, please tell me (or direct me on the right path - where you can read, study this topic)
there is a scheme:
Load balancer (2 pcs.) -> servers with a website (5 pcs.) -> Database (2 servers)
from here questions :
1. You need to make 2 servers with one (common) database, where the servers with the site (5pcs) access. How to implement all this? (preferably a lot of Russian links)
2. The client authorizes on the site (let's say on server 3, which is currently connected to server number 1 with a database), when the page is updated, the balancer sends the client to server number 4, which is currently connected to server number 2 with base. Does he need to log in again? Where can I read by sessions?
3. If you made any changes to the site files, do you need these changes by hand on all (in this case, 5) servers?
4. What other pitfalls can be? Give more information to anyone who has experienced this.

Answer 1

I recommend to get acquainted with RuHighload

Answer 2

HAproxy( or nginx) -> 5 sites -> HAproxy(without nginx) -> 2 mariadb(master-master galera cluster)
/var/www/your-site -> lsyncd -> between five sites