I see, the default docker installer for fail2ban gave me an error because “Port 80 was already in use” (by NGINX Manager).
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)