Apache2 Configuration That Allows a Subdomain Point to an Machine:Port - ruby-on-rails

Question

I own the domain, "peterlee.com.cn", and I added an A Record in my domain control panel:
RR Destination IP TTL
rs.peterlee.com.cn 10.50.10.75 1 hour
I have an RoR (Ruby on Rails) project running on 10.50.10.75:9051, which means the user can visit my RoR application by http://10.50.10.75:9051
I want to let the user visit it by http://rs.peterlee.com.cn, so I added the following VirtualHost File/Site:
<VirtualHost *:80>
ServerName rs.peterlee.com.cn
DocumentRoot /usr/website/myapp/current/public
PassengerEnabled off
ProxyPass / http://127.0.0.1:9051/
ProxyPassReverse / http://127.0.0.1:9051/
RackEnv production
RailsEnv production
<IfModule mod_rewrite.c>
RewriteEngine On
# Redirect all requests to the maintenance page if present
RewriteCond %{REQUEST_URI} !\.(css|gif|jpg|png)$
RewriteCond %{DOCUMENT_ROOT}/system/maintenance.html -f
RewriteCond %{SCRIPT_FILENAME} !maintenance.html
RewriteRule ^.*$ /system/maintenance.html [L]
</IfModule>
</VirtualHost>
After enabling the site and restarting the Apache2, I tried http://rs.peterlee.com.cn, it gives me the 500 Internal Server Error:
Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, [no address given] and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Apache/2.2.22 (Ubuntu) Server at rs.peterlee.com.cn Port 80
Thanks.
Peter

Answer 1

I found the following warning in /var/log/apache2/error.log:
[Thu Jul 19 10:22:20 2012] [warn] proxy: No protocol handler was valid for the URL /. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.
[Thu Jul 19 10:22:20 2012] [warn] proxy: No protocol handler was valid for the URL /favicon.ico. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.
So I enable the following modules:
sudo a2enmod proxy proxy_balancer proxy_http
After restarting Apache2, it worked!
Thanks anyway.
BTW: I start the service using Passenger:
passenger start -a 127.0.0.1 -p 9051 -e production -d