nginx.conf

server {
    listen 80;
    listen [::]:80;
    server_name yourserver.com;

    root /path/to/your/htdocs;

    error_page 404 /404.html
    index index.html;

    location ~ /\. {
        deny all;
    }

    location / {
        try_files $uri @prerender;
    }

    location @prerender {
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        #proxy_intercept_errors on;

        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:3000;
            proxy_pass http://prerender.herokuapp.com;
        }
        if ($prerender = 0) {
            rewrite .* /index.html break;
        }
    }
}