Debian 11, Apache 2.4.56, PHP 7.4.33, ispconfig 3.2.9p1 This server was basically created by following the perfect server Debian 10 guide in conjunction with the debian 11 update guide. The only vhost with SSL is the ispconfig admin interface, so acme.sh is working as expected. The websites will eventually have SSL as well. I create the first site ABCDEFG.com. No SSL, PHP, no auto-subdomain, as simple as possible, let server.php finish, and I am able to verify client0/web1 site is online and showing the default ISPconfig3 index page. Everything works perfectly as expected. I create the second site XYZ.com with otherwise same config as web1. client0/web2 is created, but instead of the ISPconfig standard_index.html, it shows the debian content from /var/www/html/index.html! Puzzled, I then created XYZ2.com, XYZ3.com, XYZ4.com same as before, and they ALL work properly and show their respective standard_index.html content. Then I delete client0/web2, and rename for example XYZ3.com to XYZ.com, and now this site is also showing the default apache debian page! I tried this site rename exercise a few times to make sure I wasn't crazy. I have seen strange behavior before with SNI and a mix of SSL and non-SSL sites, but not like this. It's like my XYZ.com domain is specifically confusing to apache or something. httpd error logs are empty for this site.
You are probably using a wrong system hostname. The system hostname must be a subdomain not used as a website in apache. So you should use a linux system hostname like server1.yourdomain.tld and not yourdoamin.tld and do not create server1.yourdomain.tld as website in apache. Btw, this is not ISPConfig specific, that#s the case on all apache systems.
That much I do know, but you're right, /etc/hostname also showed web01.blahblah.com instead of simply "web01." I like to avoid FQDN altogether in the hostname file. After a reboot we're back to normal behavior. Thank you for pointing me in the right direction so quickly. Since this is my first post here, this is also my first chance to say I've been using ISPConfig for over 11 years and this is the first time I have needed help, and of course it is you who comes immediately with the answer. Thank you for all of your work and - I can't emphasize enough - heading up BAR NONE the ABSOLUTE FINEST open source project of any kind and with impeccable representation.