DNS and Discourse

The httpd is running on 443. This is the website example.com. The forum should run in a subdomain forum.example.com. Which Port I have to use?

Here is the output of netstat -alpn | grep 443

[root@vserver ~]# netstat -alpn | grep 443
tcp        0      0 0.0.0.0:8443            0.0.0.0:*               LISTEN      28853/sw-cp-server: 
tcp        0      0 178.77.99.191:8443      185.243.71.165:58504    TIME_WAIT   -                   
tcp        0      0 178.77.99.191:8443      185.243.71.165:58482    TIME_WAIT   -                   
tcp        0      0 178.77.99.191:8443      185.243.71.165:58514    TIME_WAIT   -                   
tcp6       0      0 :::443                  :::*                    LISTEN      2517/httpd          
tcp6       0      0 :::8443                 :::*                    LISTEN      28853/sw-cp-server: 
tcp6       0      0 178.77.99.191:443       185.243.71.165:46544    TIME_WAIT   -                   
tcp6       0      0 178.77.99.191:443       185.243.71.165:46542    TIME_WAIT   -