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

It is very strange, because Docker sets up its FORWARD chain's policy as "drop" (for a reason). But in your case it is accept for some reason.