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About

Fail2ban Docker image based on Alpine Linux.
If you are interested, check out my other Docker images!

💡 Want to be notified of new releases? Check out 🔔 Diun (Docker Image Update Notifier) project!


Build locally

git clone https://github.com/crazy-max/docker-fail2ban.git
cd docker-fail2ban

# Build image and output to docker (default)
docker buildx bake

# Build multi-platform image
docker buildx bake image-all

Image

Registry Image
Docker Hub crazymax/fail2ban
GitHub Container Registry ghcr.io/crazy-max/fail2ban

Following platforms for this image are available:

$ docker run --rm mplatform/mquery crazymax/fail2ban:latest
Image: crazymax/fail2ban:latest
 * Manifest List: Yes
 * Supported platforms:
   - linux/amd64
   - linux/arm/v6
   - linux/arm/v7
   - linux/arm64
   - linux/386
   - linux/ppc64le
   - linux/s390x

Environment variables

  • TZ: The timezone assigned to the container (default UTC)
  • F2B_LOG_TARGET: Set the log target. This could be a file, SYSLOG, STDERR or STDOUT (default STDOUT)
  • F2B_LOG_LEVEL: Log level output (default INFO)
  • F2B_DB_PURGE_AGE: Age at which bans should be purged from the database (default 1d)
  • SSMTP_HOST: SMTP server host
  • SSMTP_PORT: SMTP server port (default 25)
  • SSMTP_HOSTNAME: Full hostname (default $(hostname -f))
  • SSMTP_USER: SMTP username
  • SSMTP_PASSWORD: SMTP password
  • SSMTP_TLS: Use TLS to talk to the SMTP server (default NO)
  • SSMTP_STARTTLS: Specifies whether ssmtp does a EHLO/STARTTLS before starting SSL negotiation (default NO)

💡 SSMTP_PASSWORD_FILE can be used to fill in the value from a file, especially for Docker's secrets feature.

Volumes

  • /data: Contains customs jails, actions and filters and Fail2ban persistent database

Usage

Docker Compose

Docker compose is the recommended way to run this image. Copy the content of folder examples/compose in /var/fail2ban/ on your host for example. Edit the compose and env files with your preferences and run the following commands:

docker-compose up -d
docker-compose logs -f

Command line

You can also use the following minimal command :

docker run -d --name fail2ban --restart always \
  --network host \
  --cap-add NET_ADMIN \
  --cap-add NET_RAW \
  -v $(pwd)/data:/data \
  -v /var/log:/var/log:ro \
  crazymax/fail2ban:latest

Upgrade

Recreate the container whenever I push an update:

docker-compose pull
docker-compose up -d

Notes

DOCKER-USER chain

In Docker 17.06 and higher through docker/libnetwork#1675, you can add rules to a new table called DOCKER-USER, and these rules will be loaded before any rules Docker creates automatically. This is useful to make iptables rules created by Fail2Ban persistent.

If you have an older version of Docker, you may just change the chain definition for your jail to chain = FORWARD. This way, all Fail2Ban rules come before any Docker rules but these rules will now apply to ALL forwarded traffic.

More info : https://docs.docker.com/network/iptables/

DOCKER-USER and INPUT chains

If your Fail2Ban container is attached to DOCKER-USER chain instead of INPUT, the rules will be applied only to containers. This means that any packets coming into the INPUT chain will bypass these rules that now reside under the FORWARD chain.

This is why the sshd jail contains a chain = INPUT in its definition and traefik jail contains chain = DOCKER-USER.

Jails examples

Here are some examples using the DOCKER-USER chain:

And others using the INPUT chain:

Use iptables tooling without nftables backend

As you may know, nftables is available as a modern replacement for the kernel's iptables subsystem on Linux.

This image still uses iptables to preserve backwards compatibility but an issue is opened about its implementation.

If your system's iptables tooling uses the nftables backend, this will throw the error stderr: 'iptables: No chain/target/match by that name.'. You need to switch the iptables tooling to 'legacy' mode to avoid these problems. This is the case on at least Debian 10 (Buster), Ubuntu 19.04, Fedora 29 and newer releases of these distributions by default. RHEL 8 does not support switching to legacy mode, and is therefore currently incompatible with this image.

On Ubuntu or Debian:

update-alternatives --set iptables /usr/sbin/iptables-legacy
update-alternatives --set ip6tables /usr/sbin/ip6tables-legacy
update-alternatives --set arptables /usr/sbin/arptables-legacy
update-alternatives --set ebtables /usr/sbin/ebtables-legacy

On Fedora:

update-alternatives --set iptables /usr/sbin/iptables-legacy

Then reboot to apply changes.

Use fail2ban-client

Fail2ban commands can be used through the container. Here is an example if you want to ban an IP manually :

docker exec -t <CONTAINER> fail2ban-client set <JAIL> banip <IP>

Global jail configuration

You can provide customizations in /data/jail.d/*.local files.

For example to change the default bantime for all jails, send an e-mail with whois report and relevant log lines to the destemail:

[DEFAULT]
bantime = 1h
destemail = root@localhost
sender = root@$(hostname -f)
action = %(action_mwl)s

⚠️ If you want email to be sent after a ban, you have to configure SSMTP env vars

FYI, here is the order jail configuration would be loaded:

jail.conf
jail.d/*.conf (in alphabetical order)
jail.local
jail.d/*.local (in alphabetical order)

A sample configuration file is available on the official repository.

Custom jails, actions and filters

Custom jails, actions and filters can be added respectively in /data/jail.d, /data/action.d and /data/filter.d. If you add an action/filter that already exists, it will be overriden.

⚠️ Container has to be restarted to propagate changes

Contributing

Want to contribute? Awesome! The most basic way to show your support is to star the project, or to raise issues. You can also support this project by becoming a sponsor on GitHub or by making a Paypal donation to ensure this journey continues indefinitely!

Thanks again for your support, it is much appreciated! 🙏

License

MIT. See LICENSE for more details.