Site does not work on PHP-FPM handler on Plesk server: 503 service unavailable

Symptoms

• Domain example.com does not work:

  PLESK_INFO: 503 service unavailable

  ---

  PLESK_INFO: 502 Bad Gateway
  Nginx

• The following error appears in domain's error log /var/www/vhosts/system/example.com/logs/error_log:

  CONFIG_TEXT: [proxy:error] [pid 15065:tid 139826443527936] (111)Connection refused: AH02454: FCGI: attempt to connect to Unix domain socket /data/vhosts/system/example.com/php-fpm.sock (*) failed
  [proxy_fcgi:error] [pid 15065:tid 139826443527936] [client 203.0.113.2:50232] AH01079: failed to make connection to backend: httpd-UDS

Cause

Configuration file for a domain is missing in /opt/plesk/php/X.X/etc/php-fpm.d/ directory.

Resolution

Regenerate the configuration:

1. Log into Plesk.
2. Go to Domains > example.com > PHP Settings and change PHP handler to different one and click OK
3. Change PHP handler version back and click OK.

If multiple domains are affected:

1. Connect to the server via SSH;

   Note: if direct SSH access to the server is not possible, contact server administrator for further assistance.

2. Execute the following command to update settings on all domains:

   # /usr/local/psa/bin/php_settings -u

3. Restart PHP handler processes, for example:

   # systemctl restart plesk-php74-fpm