Re: docker firewall?

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On 8/20/23 10:05, Oleg Cherkasov wrote:
On 19.08.2023 16:48, Alex wrote:
I'm a long-time Linux sysadmin but haven't done much with docker and containers or firewalls beyond iptables. I have inherited a fedora38 system where another admin has installed python3-docker, but port 8080 is now exposed to the Internet.

I have a basic iptables firewall that I set up some time ago (when the system was probably fedora35), but iptables also shows some docker rules:

# iptables -nvL|grep ^Chain|grep DOCKER
Chain DOCKER (2 references)
Chain DOCKER-ISOLATION-STAGE-1 (1 references)
Chain DOCKER-ISOLATION-STAGE-2 (2 references)

Where do these chains/policies come from? Is it also an iptables firewall or is it using ufw?

Why wouldn't it use firewall-cmd? Isn't that the default desktop firewall app now for fedora?

The docker doesn't play well with ufw or firewalld, in my experience. It customizes rules directly, which makes it difficult to control with publicly available networks.  The simplest way to do firewall customization is to turn off firewall customization in the docker and do it manually.

Firstly, update docker.service to include the following option (--iptables=false):

ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

Restart the Docker service and verify the existence of the Docker zone if using firewalld:

docker (active)
  target: ACCEPT
  icmp-block-inversion: no
  interfaces: br-custom1 br-custom2 docker0
  masquerade: no
  rich rules:

Add the available docker bridge interfaces (br-custom* and docker0) to the docker zone.  Check if the target zone is ACCEPT instead of default.

I hope that helps.

You could always switch to using Podman, which will not open the port on the host by default.
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