An Apache configuration for a Seaside server behind it may look like

<VirtualHost *:80>
    ServerAdmin email.address@tideland.biz
    ServerName webapp.tideland.biz
    RewriteEngine On
    ProxyVia Block
    ProxyPreserveHost On
    RewriteCond /var/www/webapp/%{REQUEST_FILENAME} !-f
    RewriteRule ^/(.*)$ http://localhost:9090/seaside/webapp/$1 [P,L]
</VirtualHost>