Error message appears in Plesk after enabling LiteSpeed: New configuration files for the Apache web server were not created due to the errors in configuration templates

Symptoms

• Plesk Obsidian running on a Linux server that has an active LiteSpeed Web Server license
• The following error message appears in the Plesk GUI after enabling the LiteSpeed webserver via the LiteSpeed Extension for Plesk:

PLESK_ERROR: New configuration files for the Apache web server were not created due to the errors in configuration templates: Can not restart web server: apache_control_adapter[9820]: Apache is down, start it instead of graceful apache_control_adapter[9820]: httpd stop failed apache_control_adapter[9820]: 0 /usr/sbin/httpd processes are killed apache_control_adapter[9820]: apache_action(graceful): invoke_httpd_action failed, trying second time apache_control_adapter[9820]: Apache is down, start it instead of graceful apache_control_adapter[9820]: httpd stop failed apache_control_adapter[9820]: 1 /usr/sbin/httpd processes are killed INFO: [Sun Mar 26 12:26:48 EST 2023]: Service: apache, Action: start Trying to start service httpd... activating Mar 26 12:26:49 hostname systemd[1]: Failed to start The Apache HTTP Server. Mar 26 12:26:49 hostname systemd[1]: Unit httpd.service entered failed state. Mar 26 12:26:49 hostname systemd[1]: httpd.service failed. ***** problem report ***** Warning: start service httpd failed /usr/local/psa/admin/sbin/pleskrc execution failed: Job for httpd.service failed because the control process exited with error code. See "systemctl status httpd.service" and "journalctl -xe" for details.. Detailed error descriptions were sent to you by email. Please resolve the issues and click here to generate broken configuration files once again or here to generate all configuration files. See the details in Configuration Troubleshooter

• The websites are working via the LiteSpeed webserver with no issues.

• Apache service isn't running and there are no stuck Apache processes. The following command returns no output (or returns LiteSpeed processes):

  Click on a section to expand

  For a RHEL-based OS:

  # ps auxffww | grep -i httpd | grep -v "grep"

  For a Debian-based OS:

  # ps auxffww | grep -i apache2 | grep -v "grep"

• There are no Apache configuration syntax errors:
  Click on a section to expand
  For a RHEL-based OS:

  # httpd -t
  Syntax OK

  For a Debian-based OS:

  # apache2 -t
  Syntax OK

Cause

Some leftover broken Apache configuration files have remained on the server. They are still being detected as broken and are causing the mentioned error to appear.

Resolution

Note: In order to finish the reconfiguration (and get rid of the error message), it's necessary to disable LiteSpeed temporarily, which will bring down all the websites.