ip direct access with port is normal, the speed is OK, the access speed of domain name is very slow, sometimes it can"t be opened, how to optimize it

    server 
    { 
        listen 80;
        server_name www.xxx.com;
        rewrite ^(.*) https://www.xxx.com permanent;
    }


    server {
        listen       443 ssl http2 default_server;
        listen       [::]:443 ssl http2 default_server;
        server_name  www.xxx.com;
        root         /usr/share/nginx/html;

        ssl_certificate /usr/local/nginx/conf/vhost/cert/www.xxx.com.cer;
        ssl_certificate_key /usr/local/nginx/conf/vhost/cert/www.xxx.com.key;
        ssl_session_cache shared:SSL:1m;
        ssl_session_timeout  10m;
        ssl_ciphers HIGH:!aNULL:!MD5;
        ssl_prefer_server_ciphers on;

        -sharp Load configuration files for the default server block.
        include /etc/nginx/default.d/*.conf;

        location / {
            proxy_pass http://127.0.0.1:8001;
        }

        error_page 404 /404.html;
            location = /40x.html {
        }

        error_page 500 502 503 504 /50x.html;
            location = /50x.html {
        }
    }