Is mydomain.lan just a placeholder or does this servers domain only resolve inside of your network? If the latter then the issue is that your visitors aren’t inside that network and therefore can’t send their data to mydomain.lan
visitors go to my local web server via the url https://nextcloud.mydomain.com which also have the local url https://nextcloud.mydomain.lan, but of course external visitor only know the url https://nextcloud.mydomain.com
https://nextcloud.mydomain.com and https://nextcloud.mydomain.lan know who is http://nagios.mydomain.lan/piwik/ and http://ip_of_server/piwik/
same thing for https://wiki.mydomain.com
I must create the server with url http://nagios.mydomain.com/piwik/ ? I don’t want to do that, i don’t want give a .com to a my piwik server.