Customer wants to direct two domains to same folder (they have some software solution for what to show, depending on domain). How to do it correctly ? If I deactivate one site and make aliasdomain I expect problems with certificates. I really don't want manualy edit vhost file, this screams for problems.
Which software do you use to manage the system? As you post outside of the ISPConfig forum section, I must guess it must be a different panel. If you had used ISPConfig on this server, then this would be really easy and straight forward as all you have to do is to create a website for domain1 and then add an alias domain for domain2. No redirects or other settings are required. And on ISPConfig servers, you never have to edit vhosts manually anyway.
Sorry, posted in wrong section. We are using ispconfig, that's wha I really don't want any manual work. Already found out that I have to create aliasdomain and after that request new let's encrypt certificate so both domains will be included
Requesting a new LE cert is unnecessary, as alias and subdomains get added to the site's LE cert automatically. Just take care that the second domain points to the server in DNS before you add it as alias domain.