nginx maintenance mode

maintenance-mode.conf

server {
        listen      80;
        server_name mysite.com;
        root    /var/www/mysite.com/;

        location / {
            if (-f $document_root/maintenance.html) {
                return 503;
           }
            ... # the rest of your config goes here
         }

        error_page 503 @maintenance;
        location @maintenance {
                rewrite ^(.*)$ /maintenance.html break;
        }
}

Now whenever you need to take your site offline, simply create the file maintenance.html in the $document_root (in our case, /var/www/mysite.com). If the file exists, Nginx will serve it with a 503 status code, if not, it will proceed as usual.

https://lincolnloop.com/blog/pro-tip-redirecting-custom-nginx-maintenance-page/