Steps
=====

1. Set up mongrel_cluster

follow: http://mongrel.rubyforge.org/docs/mongrel_cluster.html

run it with user ioi:ioi


2. Set up Apache

in general follow: 
http://mongrel.rubyforge.org/docs/apache.html

2.1 enable mods

run:
sudo a2enmod rewrite
sudo a2enmod proxy
sudo a2enmod proxy_balancer
sudo a2enmod proxy_http
sudo a2enmod deflate
sudo a2enmod headers

2.2 edit virtual host at /etc/apache2/site-(available|enabled)

added:
===========================================
<directory "/home/ioi/web_grader/public/">
  Options FollowSymLinks
  AllowOverride None
  Order allow,deny
  Allow from all
</directory>

<proxy balancer://mongrel_cluster>
  BalancerMember http://127.0.0.1:8000
  BalancerMember http://127.0.0.1:8001
  BalancerMember http://127.0.0.1:8002
  BalancerMember http://127.0.0.1:8003
  BalancerMember http://127.0.0.1:8004
  Allow from all
</proxy>

# can't use proxypass because we want access to balancer-manager
#ProxyPass / balancer://mongrel_cluster/
#ProxyPassReverse / balancer://mongrel_cluster/

<Location /balancer-manager>
  SetHandler balancer-manager
</Location>

RewriteEngine On

# Uncomment for rewrite debugging
RewriteLog "/var/log/apache2/ioi_rewrite.log"
RewriteLogLevel 9

# Rewrite to check for Rails cached page
RewriteRule ^([^.]+)$ $1.html [QSA]

# Redirect all non-static requests to cluster
RewriteCond %{REQUEST_URI} !^/balancer-manager/(.*)$
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
RewriteRule ^/(.*)$ balancer://mongrel_cluster%{REQUEST_URI} [P,QSA,L]
===========================================