In my DigitalOcean (DO) droplet I installed this image: Ubuntu Docker 17.12.0~ce on 16.04 (which is available on ** DO website > droplet> destroy> rebuild droplet**) , in ssh (after user configuration), I run
sudo ufw default deny incoming
sudo ufw default allow outgoing
sudo ufw enable
sudo ufw status verbose
and get:
Status: active
Logging: on (low)
Default: deny (incoming), allow (outgoing), allow (routed)
New profiles: skip
To Action From
-- ------ ----
22 LIMIT IN Anywhere
2375/tcp ALLOW IN Anywhere
2376/tcp ALLOW IN Anywhere
22 (v6) LIMIT IN Anywhere (v6)
2375/tcp (v6) ALLOW IN Anywhere (v6)
2376/tcp (v6) ALLOW IN Anywhere (v6)
As you see, I don't allow any connections on port 80 (http). Ok to test that firewall really works I run following docker:
sudo docker run -d -p 80:80 -e ENABLE_IPV6=true -v /var/run/docker.sock:/tmp/docker.sock:ro jwilder/nginx-proxy:alpine
But when I go to chrome and type my droplet IP I see nginx response (!!!)
I try this also for Ubuntu 17 image (with docker installation by hand) but still get the same problem.
Conclusion: ufw firewall doesn't work at all in Ubuntu
Question: how to configure ufw/Ubuntu to fix this problem?
Docker and UFW don't work together too well as they both modify iptables but there's a way to fix this. You'll need to configure Docker to not use iptables. Add
DOCKER_OPTS="--iptables=false"
to /etc/default/docker and restart your host (or restart the Docker daemon and UFW).
These two links have a lot more information about the issue:
https://blog.viktorpetersson.com/2014/11/03/the-dangers-of-ufw-docker.html
https://www.techrepublic.com/article/how-to-fix-the-docker-and-ufw-security-flaw/