@ Syrius: Danke das werde ich mir auch noch anschauen.

/etc/nginx/nginx.conf
Code:
user nginx;
worker_processes  2;   # Set to number of CPU cores

pid  /run/nginx.pid;

events {
    worker_connections  1024;
}

http {

	##
	# Basic Settings
	##

	sendfile on;
	keepalive_timeout 65;
	include /etc/nginx/mime.types;
	default_type application/octet-stream;

	##
	# Logging Settings
	##

	access_log /var/log/nginx/access.log;
	error_log /var/log/nginx/error.log;

  log_format  main '$remote_addr - $remote_user [$time_local] "$request" '
              '$status $body_bytes_sent "$http_referer" '
              '"$http_user_agent" "$http_x_forwarded_for"';



	# add into "server" section

   server {
	listen SERVER_IP_PROXY:80;

	server_name  www.domain1.com domain1.com;
	
location  / {
    proxy_buffering  off;
    proxy_pass  http://BACKEND_SERVER_IP:80;
  }
}

server {
	listen SERVER_IP_PROXY:80;

	server_name  www.domain2.com domain2.com;
	
location  / {
    proxy_buffering  off;
    proxy_pass  http://BACKEND_SERVER_IP:80;
  }
}

		  
	##
	# Virtual Host Configs
	##

	# include /etc/nginx/conf.d/*.conf;
	# include /etc/nginx/sites-enabled/*;
}

Der Backend hört auf Port 80.
Wichtig ist auch das ich die IP des Besuchers im access.log am Backend erhalte.