Configure UFW to manage Docker related connections

Prologue

This guide applies to Ubuntu 20.04. After you installed docker and setup UFW to block all connections by default, docker will bypass the firewall entirely.

To fix this issue follow this guide to configure Docker and UFW to properly work together.

/etc/docker/daemon.json

Start by creating/editing following file: /etc/docker/daemon.json

{
"iptables": false
}

/etc/ufw/after.rules

Then you need to edit following file as well: /etc/ufw/after.rules

Make sure to paste following lines before the last line in the file which is COMMIT

Also adjust ens3 to your default interface name.

# Put Docker behind UFW
*filter
:DOCKER-USER - [0:0]
:ufw-user-input - [0:0]

-A DOCKER-USER -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A DOCKER-USER -m conntrack --ctstate INVALID -j DROP
-A DOCKER-USER -i ens3 -j ufw-user-input
-A DOCKER-USER -i ens3 -j DROP
# End Docker UFW rules

Once you've done this, execute following commands to apply your changes:

This will restart all your docker containers.

sudo systemctl restart ufw

sudo systemctl restart docker

Test your configuration to make sure the changes are working.