Actually, we do want to run fail2ban on all hosts because the sshd
monitoring via systemd is nice. At the very least it reduces spam
from failed logins in our systemd journal.
We can only run fail2ban when we have logs to monitor. When a host
is running Caddy we don't have logs, so fail2ban doesn't have any-
thing to monitor out of the box. For now I will restrict the task
to hosts running nginx.
According to Ansible we can use yes, true, True, "or any quoted st-
ring" for a boolean true, but ansible-lint wants us to use either
true or false.
See: https://chronicler.tech/red-hat-ansible-yes-no-and/
Some hosts can use fail2ban's nginx-botsearch filter to ban anyone
making requests to non-existent files like wp-login.php. There is
no reason to request such files naively and anyone found doing so
can be banned immediately.
In theory I should report them to AbuseIPDB.com, but that will take
a little more wiring up.
This is active banning of IPs that are brute forcing login attempts
to SSH, versus the passive banning of 10,000 abusive IPs from the
abuseipdb.com blacklist. For now I am banning IPs that fail to log
in successfully more than twelve times in a one-hour period, but
these settings might change, and I can override them at the group
and host level if needed.
Currently this works for CentOS 7, Ubuntu 16.04, and Ubuntu 18.04,
with minor differences in the systemd configuration due to older
versions on some distributions.
You can see the status of the jail like this:
# fail2ban-client status sshd
Status for the jail: sshd
|- Filter
| |- Currently failed: 0
| |- Total failed: 0
| `- Journal matches: _SYSTEMD_UNIT=sshd.service + _COMM=sshd
`- Actions
|- Currently banned: 1
|- Total banned: 1
`- Banned IP list: 106.13.112.20
You can unban IPs like this:
# fail2ban-client set sshd unbanip 106.13.112.20
Alan Orth