Mixed-case domains do not work on PHP-FPM by Apache: 503 service unavailable

Symptoms

• Domains or subdomains with upper case letters in the name like Example.Com do not work on PHP-FPM by Apache handler:

  503 Service Unavailable

• The following error is shown in Domains > Example.Com > Logs:
  

  [proxy:error] [pid 27291:tid 140336512890624] (2)No such file or directory: AH02454: FCGI: attempt to connect to Unix domain socket /var/www/vhosts/system/example.com/php-fpm.sock failed

• Apache version is lower than 2.4.14 in Tools & Settings > Server Components.

Cause

Apache's bug PR 57968, and identified as bug #PPP-31339 that is fixed in Plesk Obsidian no matter what Apache version is used.

Resolution

Upgrade to the latest Plesk version, as the upgrade will fix the issue for all newly created domains.

To fix the issue for all already existing domains after the upgrade, use the following workaround:

1. Log in to Plesk

2. Rename the affected domain temporarily in order to re-generate the correct ASCII naming:

   Domains > Example.Com > Hosting Settings : rename a domain to any other name, for example, newExample.Com

   Note: Do not try to rename it to lower case, as it will not be allowed showing the message: "This domain name already exists."

   Domains > newExample.Com > Hosting Settings : Rename the domain back to the correct name, for example back to Example.Com

Additional information

https://bz.apache.org/bugzilla/show_bug.cgi?id=57968
https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x/CHANGES