Environment

1. A records in DNS manager
   | Type | Name | Value |
   | A | blog | your_server_ip |
   | A | math | your_server_ip |
2. Set up apache2 with this https://certbot.eff.org/
3. Add necessary module

a2enmod proxy proxy_http proxy_wstunnel proxy_balancer lbmethod_byrequests
systemctl restart apache2

HTML Codes

        var ws_link = 'ws://' + location.hostname + "/ws/";
        if (window.location.protocol === 'https:') {
            ws_link = 'wss://' + location.hostname + "/wss/";
        }
        var ws = new WebSocket(ws_link);

Apache Codes (at /etc/apache2/sites-available/000-default.conf)

<VirtualHost *:80>
        ServerName blog.yingshaoxo.xyz

        ProxyRequests Off
        ProxyPreserveHost On

        ProxyPass        "/" "http://127.0.0.1:2018/"
        ProxyPassReverse "/" "http://127.0.0.1:2018/"
</VirtualHost>


<VirtualHost *:80>
        ServerName math.yingshaoxo.xyz

        ProxyRequests Off
        ProxyPreserveHost On

        ProxyPass "/ws/" "ws://127.0.0.1:5277/"
        ProxyPassReverse "/ws/" "ws://127.0.0.1:5277/"

        ProxyPass "/wss/" "ws://127.0.0.1:5277/"
        ProxyPassReverse "/wss/" "ws://127.0.0.1:5277/"

        ProxyPass        "/" "http://127.0.0.1:5000/"
        ProxyPassReverse "/" "http://127.0.0.1:5000/"
</VirtualHost>

Finnaly

systemctl restart apache2