Configure UFW to manage Docker related connections

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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.

/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

# 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:

Small Warning.png 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.