Fail2ban does not listen on any port for it has no user interface. No interface at all actually. It’s just a process that monitors your logfiles and changes firewall rules and writes to syslog if you tell it to.

I run it on internet facing servers so I use a ‘regular’ install and never docker. I see no advantage for docker in this case, but one huge disadvantage: Docker changes a lot on the network side. It creates bridges, and picks IP’s all by itself. I hate that. (I know you can put in a lot of effort to manage it, but no thanks stay of my network config thank you)