nginx subdomain configuration for multiple rails apps

auto-sd

# source: http://server-tuning.info/nginx/auto-subdomains-nginx.html
server {
    listen 80;
    server_name example.com *.example.com;
    passenger_enabled on;
    rails_env    production;
    root /path/to/project/$subdomain/current/public;
    set $subdomain "";
    if ($host ~* ^([a-z0-9-\.]+)\.zstaging.xyz$) {
        set $subdomain $1;
    }
    if ($host ~* ^www.example.com$) {
        set $subdomain "";
    }
}