Fail2ban does not start on a Plesk server with Ubuntu 24: No module named 'asynchat'

Symptoms

• On a brand-new install of Plesk for Linux on an Ubuntu 24.04 server, fail2ban service does not start.

• The following information can be seen on systemctl status fail2ban

  CONFIG_TEXT: May 17 15:32:25 server.example.com systemd[1]: Starting fail2ban.service - Fail2Ban Service...
  May 17 15:32:25 server.example.com systemd[1]: Started fail2ban.service - Fail2Ban Service.
  May 17 15:32:25 server.example.com fail2ban-server[128927]: 2024-05-17 15:32:25,412 fail2ban.configreader [128927]: WARNING 'allowipv6' not defined in 'Definition'.
  May 17 15:32:25 server.example.com fail2ban-server[128927]: 2024-05-17 15:32:25,449 fail2ban [128927]: ERROR No module named 'asynchat'
  May 17 15:32:25 server.example.com systemd[1]: fail2ban.service: Main process exited, code=exited, status=255/EXCEPTION
  May 17 15:32:25 server.example.com systemd[1]: fail2ban.service: Failed with result 'exit-code'.

Cause

Fail2Ban is incompatible with Python 3.12 due to a known issue:

• https://bugs.launchpad.net/ubuntu/+source/fail2ban/+bug/2055114

Resolution

As a workaround, install pyasynchat:

1. Connect to the server via SSH

2. Install PIP (Package Installer for Python):

   # apt install python3-pip

3. Install pyasynchat package:

   # python3 -m pip install pyasynchat --break-system-packages

4. Start Fail2ban service

   # systemctl start fail2ban