server {
    listen 80;
    server_name ~^(?<subdomain>\w*)\.${DOMAIN}.${ZONE}${DOLLAR};

    location / {
        if ($http_x_subdomain = "") {
            set $http_x_subdomain $subdomain;
        }
        proxy_set_header X-Subdomain $http_x_subdomain;
        proxy_pass http://${SERVER}:${SERVER_PORT}/;
    }
}

server {
    listen 80;
    server_name ${DOMAIN}.${ZONE};

    location / {
        proxy_pass http://${SERVER}:${SERVER_PORT}/;
    }
}