Website becomes unavailable after switching to FPM application served by Apache

Symptoms

• Website becomes unavailable after switching to FPM application served by Apache

• When the PHP version to another one and then back to the initial PHP version the website works again

• In the corresponding /var/log/plesk-phpXX-fpm/error.log the following errors appear despite the fact that the service is running and the website is accessible:

  ERROR: Another FPM instance seems to already listen on /var/www/vhosts/system/example.com/php-fpm.sock
  ERROR: Another FPM instance seems to already listen on /var/www/vhosts/system/example.com/php-fpm.sock
  ERROR: Another FPM instance seems to already listen on /var/www/vhosts/system/example.com/php-fpm.sock
  ERROR: Another FPM instance seems to already listen on /var/www/vhosts/system/example.com/php-fpm.sock

Cause

The php-fpm.sock file of the affected domain is corrupted

Resolution

Delete the php-fpm.sock file, it will be recreated automatically:

1. Connect to the server via SSH

2. Execute the following command:

   # rm -rf /var/www/vhosts/system/example.com/php-fpm.sock