Script to fix Docker iptables on Synology NAS

docker-iptables-fix.md

Instructions

• Open DSM on your Synology NAS
• Save the above file to your Synology NAS
• Open Control Panel and click on Task Scheduler
• Click Create button -> Triggered Task -> User defined script
• Give it a name, select "root" for User and "Boot-up" for Event, tick Enabled
• Click Task Settings, paste "bash /volume1/path to script" on the User-defined script
• Click OK button and you're done! The script will run after every reboot and should survive any updates of DSM!

More info

Please check the following post:

https://www.pedrolamas.com/2020/11/04/exposing-the-client-ips-to-docker-containers-on-synology-nas/

docker-iptables-fix.sh

#!/bin/bash
currentAttempt=0
totalAttempts=10
delay=15

while [ $currentAttempt -lt $totalAttempts ]
do
	currentAttempt=$(( $currentAttempt + 1 ))
	
	echo "Attempt $currentAttempt of $totalAttempts..."
	
	result=$(iptables-save)

	if [[ $result =~ "-A DOCKER -i docker0 -j RETURN" ]]; then
		echo "Docker rules found! Modifying..."
		
		iptables -t nat -A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER
		iptables -t nat -A PREROUTING -m addrtype --dst-type LOCAL ! --dst 127.0.0.0/8 -j DOCKER
		
		echo "Done!"
		
		break
	fi
	
	echo "Docker rules not found! Sleeping for $delay seconds..."
	
	sleep $delay
done