jail.local named ufw as the ban action. Two machines on this mesh have no ufw,
and fail2ban does not check: it starts, the jail reads the log, counts the
attempts, runs the ban command, gets 127 -- 'ufw: command not found' -- and
logs an error nobody reads. The service is active, the mesh reports the module
applied, and the machine is not protected. Proven by banning a documentation
address on such a machine today.
The replacement is this module's own dualchain action, already used by the
recidive jail on all four machines, so it is not a new dependency. It bans in
DOCKER-USER as well as INPUT, which ufw's action did not, and it bans all
ports, which ufw's action did.
jschoubben