Nginx reverse proxy DNS configuration - mysql

Question

I am looking to deploy an nginx/dns server on a vps proxy that maps to the real back-end in a different geographical location. The back-end runs apache,mysql,dovecot,postfix. It is a pay-for mail server. The users get entered through apache through php into mysql, and when users set up IMAP, dovecot/postfix pools them from mysql and delivers or uses the smtp outbound.
I read about something in the nginx.conf file, that I can declare the mail hostname on the proxy as so:
mail {
server_name mail.example.com;
...
}
This mail.example.com is the actual mx for the example.com mail exchanger listed in DNS? Here is where that came from:
"As you can see, we declared the name of this server at the top of the mail context.
This is because we want each of our mail services to be addressed as mail.example.
com. Even if the actual hostname of the machine on which NGINX runs is different,
and each mail server has its own hostname, we want this proxy to be a single point
of reference for our users. This hostname will in turn be used wherever NGINX
needs to present its own name, for example, in the initial SMTP server greeting."
So from my understanding, the physical hostname of the proxy should be something else besides mail.example.com. So in DNS on the proxy, I can define that as anyhost.example.com? The proxy also proxies back to my apache on the back-end.
Finally, on the back-end, how do I set up my DNS for that? What hostname do I choose for the actual box running apache,mysql,dovecot,postfix? Its all on one box. I understand that on the registrar, I point 2 nameservers, these should be two proxies, that way running a dig would only pull up the proxies and the MX which should be "known" to be on the proxy.

Answer 1

in your case where all of the services in one box including the proxy, you can set the apache, mysql and other services accessible only from localhost / 127.0.0.1. Then from nginx you put
upstream: 127.0.0.1:80
upstream: 127.0.0.1:3306
therefore the nginx is serving frontend request and forward them to designated services