Simple nginx load balancer and reverse proxy.

gistfile1.pl

upstream rails_application  {
  server 10.0.0.1 max_fails=1 fail_timeout=10s;
  server 10.0.0.2 max_fails=1 fail_timeout=10s;
  # and so on: server 10.0.0.x;
}
upstream legacy_php_application  {
  server 10.0.1.1 max_fails=1 fail_timeout=10s;
}

server {
  listen 1.2.3.4:80;
  server_name railsapp.example.com;
  location / {
    proxy_pass  http://rails_application;
  }
}

server {
  listen 1.2.3.4:80;
  server_name phpapp.example.com;
  location / {
	proxy_pass http://legacy_php_application;
  }
}