Nginx How to handle sub-domain?

I am using Centminmod on CentOS 7 and Magento 2.2.2. I added the vhost for my domain and setup the website as normal. I am currently doing the hosts file hack to access it. The website doesnt go live until the clients approve it. So I want to put it live as demo.actualdomain.com. Such that the current website is still accessible at www.actualdomain.com.

How can I achieve this? I understand that I will have to do some changes in the vhost nginx config file and add a DNS entry. Can anyone guide exactly what changes and entry I will have to make?

---

This is my current vhost config:

Code:

# Centmin Mod Getting Started Guide
# must read http://centminmod.com/getstarted.html

# redirect from non-www to www
# uncomment, save file and restart Nginx to enable
# if unsure use return 302 before using return 301
#server {
#            listen   80;
#            server_name domain.com;
#            return 301 $scheme://www.domain.com$request_uri;
#       }

server {
 
  server_name domain.com www.domain.com;

# ngx_pagespeed & ngx_pagespeed handler
#include /usr/local/nginx/conf/pagespeed.conf;
#include /usr/local/nginx/conf/pagespeedhandler.conf;
#include /usr/local/nginx/conf/pagespeedstatslog.conf;

  set $MAGE_ROOT /home/nginx/domains/domain.com/public;
  set $MAGE_MODE default;
  charset off;
  #add_header X-Frame-Options SAMEORIGIN;
  add_header X-Xss-Protection "1; mode=block" always;
  add_header X-Content-Type-Options "nosniff" always;

  # limit_conn limit_per_ip 16;
  # ssi  on;

  access_log /home/nginx/domains/domain.com/log/access.log main_ext buffer=256k flush=60m;
  error_log /home/nginx/domains/domain.com/log/error.log;

  #include /usr/local/nginx/conf/autoprotect/domain.com/autoprotect-domain.com.conf;
  #root /home/nginx/domains/domain.com/public;
  root $MAGE_ROOT/pub;

  # uncomment cloudflare.conf include if using cloudflare for
  # server and/or vhost site
  #include /usr/local/nginx/conf/cloudflare.conf;
  #include /usr/local/nginx/conf/503include-main.conf;

location /setup {
    root $MAGE_ROOT;
    location ~ ^/setup/index.php {
        include /usr/local/nginx/conf/php.conf;
    }
 
    location ~ ^/setup/(?!pub/). {
        deny all;
    }
 
    location ~ ^/setup/pub/ {
        add_header X-Frame-Options "SAMEORIGIN";
    }
}
 
location /update {
    root $MAGE_ROOT;
 
    location ~ ^/update/index.php {
        fastcgi_split_path_info ^(/update/index.php)(/.+)$;
        include /usr/local/nginx/conf/php_magento.conf;
    }
 
    # deny everything but index.php
    location ~ ^/update/(?!pub/). {
        deny all;
    }
 
    location ~ ^/update/pub/ {
        add_header X-Frame-Options "SAMEORIGIN";
    }
}

  location / {
  #include /usr/local/nginx/conf/503include-only.conf;
  # block common exploits, sql injections etc
  #include /usr/local/nginx/conf/block.conf;

  try_files $uri $uri/ /index.php?$args;
  }

location /pub {
    location ~ ^/pub/media/(downloadable|customer|import|theme_customization/.*\.xml) {
        deny all;
    }
    alias $MAGE_ROOT/pub;
    add_header X-Frame-Options "SAMEORIGIN";
}
 
location /static/ {
    if ($MAGE_MODE = "production") {
        expires max;
    }
    location ~* \.(ico|jpg|jpeg|png|gif|svg|js|css|swf|eot|ttf|otf|woff|woff2)$ {
        add_header Cache-Control "public";
        add_header X-Frame-Options "SAMEORIGIN";
        expires +1y;
 
        if (!-f $request_filename) {
            rewrite ^/static/(version\d*/)?(.*)$ /static.php?resource=$2 last;
        }
    }
    location ~* \.(zip|gz|gzip|bz2|csv|xml)$ {
        add_header Cache-Control "no-store";
        add_header X-Frame-Options "SAMEORIGIN";
        expires    off;
 
        if (!-f $request_filename) {
           rewrite ^/static/(version\d*/)?(.*)$ /static.php?resource=$2 last;
        }
    }
    if (!-f $request_filename) {
        rewrite ^/static/(version\d*/)?(.*)$ /static.php?resource=$2 last;
    }
    add_header X-Frame-Options "SAMEORIGIN";
}
 
location /media/ {
    try_files $uri $uri/ /get.php?$args;
 
    location ~ ^/media/theme_customization/.*\.xml {
        deny all;
    }
 
    location ~* \.(ico|jpg|jpeg|png|gif|svg|js|css|swf|eot|ttf|otf|woff|woff2)$ {
        add_header Cache-Control "public";
        add_header X-Frame-Options "SAMEORIGIN";
        expires +1y;
        try_files $uri $uri/ /get.php?$args;
    }
    location ~* \.(zip|gz|gzip|bz2|csv|xml)$ {
        add_header Cache-Control "no-store";
        add_header X-Frame-Options "SAMEORIGIN";
        expires    off;
        try_files $uri $uri/ /get.php?$args;
    }
    add_header X-Frame-Options "SAMEORIGIN";
}
 
location /media/customer/ {
    deny all;
}
 
location /media/downloadable/ {
    deny all;
}
 
location /media/import/ {
    deny all;
}
 
location ~ cron\.php {
    deny all;
}
 
location ~ (index|get|static|report|404|503)\.php$ {
    fastcgi_param  PHP_FLAG  "session.auto_start=off \n suhosin.session.cryptua=off";
    fastcgi_param  PHP_VALUE "memory_limit=256M \n max_execution_time=600";
    fastcgi_param  MAGE_MODE $MAGE_MODE;
    include /usr/local/nginx/conf/php.conf;
}

  #include /usr/local/nginx/conf/staticfiles.conf;
  include /usr/local/nginx/conf/php.conf;
  include /usr/local/nginx/conf/drop.conf;
  #include /usr/local/nginx/conf/errorpage.conf;
  include /usr/local/nginx/conf/vts_server.conf;
}

 

Thanks for the detailed response.

I think I wasnt clear in my initial question. There arent two domains involved. There is only one domain (lets call it abc.com). It already directs to the old website on some other server. I dont want to change that until the new website is approved. I just want demo.abc.com to direct towards the centminmod server with the new website. And once ultimately its approved, I would want to put it live at abc.com.

This is what I want:
abc.com--->old server, old website
demo.abc.com--->centminmod server, new website

 

Ok so I did this:

Code:

server {
server_name demo.abc.com www.demo.abc.com;

On the domain end, I added a new A record with centmin server IP as value and 'demo' as value. However, it first goes to the centmin server but without anything opening, it redirects to www.abc.com and the actual live website opens up.