my server: www.mydomain.com 3.4.5.6 at AWS
os: FreeBSD
www: under jail

AWS security group open 80 443
ipfw.rules forward 80, 443 to www 10.0.0.1
www has two ip 10.0.0.1 and 10.0.0.2 (setup at jail.conf)

10.0.0.1 is apache reverse proxy server (port 80)
10.0.0.2 is my real web server port 8080 (however both of them run in one apache24)

httpd.conf has to both listen port 80 and 8080

and i put my config here (automatically start)
apache24/Includes/reverse-proxy-rule.conf

# order is MATTER, /irene must go first before /
<VirtualHost *:80>
 DocumentRoot "/usr/local/www/apache24/data"
 ServerName www.mydomain.com
 ProxyRequests Off 
 ProxyPass / http://10.0.0.2:8080/ #note: 10.0.0.1 proxy data to 10.0.0.2
 ProxyPassReverse / http://10.0.0.2:8080/
</VirtualHost>