Websites can not be accessed with error 502 Bad Gateway periodically with enabled fail2ban

Symptoms

• Websites are periodically inaccessible with the following error shown in web browser:

  CONFIG_TEXT: 502 Bad Gateway

• The following records can be found in the /var/log/fail2ban.log:

  # for i in $(plesk db -Ne "select ip_address from IP_Addresses"); do grep $i /var/log/fail2ban.log | grep Ban; done
  2021-06-07 11:52:15,036 fail2ban.actions [2591]: NOTICE [plesk-wordpress] Ban 203.0.113.2

Cause

An IP address used by the server is added to Tools & Settings > IP Address Banning (Fail2Ban) because the server IP is missing in the list of trusted IP addresses in fail2ban.

Resolution