Serving instances on port 80 already used by apache

If apache already serves this port and you don't want to use Passenger, you're not stuck.

Apache comes with two nifty modules : mod_proxy and mod_proxy_balancer. So you can set-up apache as a front-end to your thin/unicorn workers. The configuration is quite straightforward. Create a VirtualHost (if needed), and add the following directives in your VirtualHost config filei :

RewriteEngine On

<Proxy balancer://thinservers>
    BalancerMember http://127.0.0.1:5000
    BalancerMember http://127.0.0.1:5001
    BalancerMember http://127.0.0.1:5002
</Proxy>

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

ProxyPass / balancer://thinservers/
ProxyPassReverse / balancer://thinservers/
ProxyPreserveHost on

<Proxy *>
      Order deny,allow
      Allow from all
</Proxy>

If you need a fallback server that responds only when other servers are dead, you can add a member in the <Proxy> directive with the status=+H option :

<Proxy balancer://thinservers>
    BalancerMember http://127.0.0.1:5000
    BalancerMember http://127.0.0.1:5001
    BalancerMember http://127.0.0.1:5002
    BalancerMember http://someserver.example.com:80 status=+H
</Proxy>