Docker nftables configuration for Debian 10

README.md

Not happy with Docker modifying your precious firewall rules?

• Docker inserts iptables rules when it's started by default
• buster uses nftables by default
• let's make Docker use nftables instead
• PROFIT

Prerequisites

Install Docker CE and nftables:

$ sudo apt-get install nftables
$ sudo systemctl --now enable nftables

Installing

Manually (create/modify daemon.json before starting docker.service):

$ sudo systemctl start docker
$ sudo systemctl stop docker containerd
$ sudo iptables-save > iptables-docker.conf
$ sudo iptables-restore-translate -f iptable-docker.conf > docker.nft
$ sudo nft flush ruleset
$ sudo nft -f docker.nft
$ sudo nft -s list ruleset > /etc/nftables-docker.conf

tl;dr

$ curl -fsSLO https://gist.github.com/goll/bdd6b43c2023f82d15729e9b0067de60/raw/nftables-docker.sh
$ sudo bash -x nftables-docker.sh

For a persistent config just overwrite /etc/nftables.conf with /etc/nftables-docker.conf

If you prefer manual start/stop you can create an alias for example:

alias dock-on='sudo nft -f /etc/nftables-docker.conf && sudo systemctl start docker'
alias dock-off='sudo systemctl stop docker containerd && sudo nft -f /etc/nftables.conf && sudo ip l d docker0'

nftables-docker.conf

table ip filter {
	chain INPUT {
		type filter hook input priority 0; policy accept;
	}

	chain FORWARD {
		type filter hook forward priority 0; policy accept;
		counter jump DOCKER-USER
		counter jump DOCKER-ISOLATION-STAGE-1
		oifname "docker0" ct state established,related counter accept
		oifname "docker0" counter jump DOCKER
		iifname "docker0" oifname != "docker0" counter accept
		iifname "docker0" oifname "docker0" counter accept
	}

	chain OUTPUT {
		type filter hook output priority 0; policy accept;
	}

	chain DOCKER {
	}

	chain DOCKER-ISOLATION-STAGE-1 {
		iifname "docker0" oifname != "docker0" counter jump DOCKER-ISOLATION-STAGE-2
		counter return
	}

	chain DOCKER-ISOLATION-STAGE-2 {
		oifname "docker0" counter drop
		counter return
	}

	chain DOCKER-USER {
		counter return
	}
}
table ip nat {
	chain PREROUTING {
		type nat hook prerouting priority -100; policy accept;
		fib daddr type local counter jump DOCKER
	}

	chain INPUT {
		type nat hook input priority 100; policy accept;
	}

	chain POSTROUTING {
		type nat hook postrouting priority 100; policy accept;
		oifname != "docker0" ip saddr 172.17.0.0/16 counter masquerade
	}

	chain OUTPUT {
		type nat hook output priority -100; policy accept;
		ip daddr != 127.0.0.0/8 fib daddr type local counter jump DOCKER
	}

	chain DOCKER {
		iifname "docker0" counter return
	}
}

nftables-docker.sh

#!/bin/bash
systemctl stop docker containerd
tee /etc/docker/daemon.json << EOF
{
  "iptables": false
}
EOF
curl -fsSLO https://gist.github.com/goll/bdd6b43c2023f82d15729e9b0067de60/raw/nftables-docker.conf -o /etc/nftables-docker.conf && nft -f /etc/nftables-docker.conf
systemctl start docker

At least in Ubuntu 22.04 /etc/nftables.conf is a script with the #!/usr/sbin/nft -f shebang. You can't just pipe nft list ruleset to there.

But you can try replacing flush ruleset with stuff like flush table inet filter for all your inet tables followed by the respective rules and never mess with ip/ip6 tables where docker does its networking stuff. In theory you'll be able to just write your nftables rules this way and then apply your changes by simply rerunning the script and that won't affect docker on a running system while also giving you persistent declarative rules.

Haven't tried that yet though.