gistfile1.txt

    location @prerender {
        set $prerender 0;
        if ($http_user_agent ~* "googlebot|yahoo|bingbot|baiduspider|yandex|yeti|yodaobot|gigabot|ia_archiver|facebookexternalhit|twitterbot|developers\.google\.com") {
            set $prerender 1;
        }
        if ($args ~ "_escaped_fragment_|prerender=1") {
            set $prerender 1;
        }
        if ($http_user_agent ~ "Prerender") {
            set $prerender 0;
        }

        if ($prerender = 1) {
            rewrite .* /$scheme://$host$request_uri? break;
            proxy_pass http://localhost:4001;
        }
        if ($prerender = 0) {
            rewrite .* /index.html break;
        }
    }