So, with this configuration, it's ok !

<VirtualHost *:80>
     
        ServerName mydomain.com

        ServerAdmin tech@tech.tech
        DocumentRoot /var/www/html

        # Available loglevels: trace8, ..., trace1, debug, info, notice, warn,
        # error, crit, alert, emerg.
        # It is also possible to configure the loglevel for particular
        # modules, e.g.
        #LogLevel info ssl:warn

        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined

        # For most configuration files from conf-available/, which are
        # enabled or disabled at a global level, it is possible to
        # include a line for only one particular virtual host. For example the
        # following line enables the CGI configuration for this host only
        # after it has been globally disabled with "a2disconf".
        #Include conf-available/serve-cgi-bin.conf

        <IfModule mod_rewrite.c>
              RewriteEngine On
                RewriteRule ^[^\/]*\/(.*) https://mydomain.com/$1 [R=301,L]
        </IfModule>

RewriteCond %{SERVER_NAME} =mydomain.com
RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
</VirtualHost>

<VirtualHost *:4567>
    ServerName subdomain.mydomain.com

    # Basic security headers
    Header always set X-Content-Type-Options "nosniff"
    Header always set X-Xss-Protection "1; mode=block"

    # NodeBB header
    RequestHeader set X-Forwarded-Proto "https"
    # Static file cache
    <FilesMatch "\.(ico|jpg|jpeg|png|gif|js|css)$">
        <IfModule mod_expires.c>
            ExpiresActive on
            ExpiresDefault "access plus 14 days"
            Header set Cache-Control "public"
        </IfModule>
    </FilesMatch>

    ProxyRequests off
    <Proxy *>
        Order deny,allow
        Allow from all
    </Proxy>

    # Custom Error Document when NodeBB is offline
    ProxyPass /error-documents !
    ErrorDocument 503 /error-documents/503.html
    Alias /error-documents path/to/nodebb/public

    # Websocket passthrough
    RewriteEngine On
    RewriteCond %{REQUEST_URI}  ^/socket.io            [NC]
    RewriteCond %{QUERY_STRING} transport=websocket    [NC]
    RewriteRule /(.*)           ws://localhost:4567/$1 [P,L]

    ProxyPass / http://localhost:4567/
    ProxyPassReverse / http://localhost:4567/

    # Log stuff
    ErrorLog ${APACHE_LOG_DIR}/nodebb-error.log
    CustomLog ${APACHE_LOG_DIR}/nodebb-access.log combined
    RewriteCond %{SERVER_NAME} =subdomain.mydomain.com
    RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
</VirtualHost>

The problem is that I had not put 2 different ServerName in the config, so all traffic was redirected and rewritten in HTTPS on the same ServerName : subdomain.mydomain.com

@per0x said in Access to my NodeBB by subdomain:

Can't you just set that up in the DNS config on your domain name ?

What do you mean?

@Dravere thnx, I'm testing this and telling you if it's okay;)

Hi there,
I'm on a Debian 8, and I try to configure my Nodebb for make an access by subdomain.mydomain.com. But, at this moment, after I do a proxy redirection in my Apache config, my Nodebb is available on mydomain.com but available too on my subdomain...
So, I would like to put only my NodeBB on my subdomain, and leave free the index of my Apache directory

How can I do that ?

My Apache configuration :

<VirtualHost *:80>
        # The ServerName directive sets the request scheme, hostname and port that
        # the server uses to identify itself. This is used when creating
        # redirection URLs. In the context of virtual hosts, the ServerName
        # specifies what hostname must appear in the request's Host: header to
        # match this virtual host. For the default virtual host (this file) this
        # value is not decisive as it is used as a last resort host regardless.
        # However, you must set it for any further virtual host explicitly.
        #ServerName www.example.com

        ServerAdmin webmaster@localhost
        DocumentRoot /var/www/html

        # Available loglevels: trace8, ..., trace1, debug, info, notice, warn,
        # error, crit, alert, emerg.
        # It is also possible to configure the loglevel for particular
        # modules, e.g.
        #LogLevel info ssl:warn

        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined

        # For most configuration files from conf-available/, which are
        # enabled or disabled at a global level, it is possible to
        # include a line for only one particular virtual host. For example the
        # following line enables the CGI configuration for this host only
        # after it has been globally disabled with "a2disconf".
        #Include conf-available/serve-cgi-bin.conf

        <Proxy *>
                Order deny,allow
                Allow from all
        </Proxy>
        ProxyPass /socket.io/1/websocket ws://127.0.0.1:4567/socket.io/1/websocket
        ProxyPassReverse /socket.io/1/websocket ws://127.0.0.1:4567/socket.io/1/websocket
        ProxyPass /socket.io/ http://127.0.0.1:4567/socket.io/
        ProxyPassReverse /socket.io/ http://127.0.0.1:4567/socket.io/
        ProxyPass / http://127.0.0.1:4567/
        ProxyPassReverse / http://127.0.0.1:4567/

</VirtualHost>

<VirtualHost *:4567>

        Servername subdomain.mydomain.com
        ServerAdmin tech@mydomain.com

        DocumentRoot /var/www/html/nodebb
        ErrorLog ${APACHE_LOG_DIR}/nodebb-error.log
        CustomLog ${APACHE_LOG_DIR}/nodebb-access.log combined

        RewriteEngine on
        RewriteCond %{SERVER_NAME} =subdomain.mydomain.com
        RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
</VirtualHost>

Thanks