Fix docker DNS not working on Linux hosts

fix-docker-dns.md

Docker DNS issues on systemd distros

(Hopefully) fix Docker DNS issues with systemd distros, e.g. ping: bad address 'google.com', Temporary failure resolving ..., EAI_AGAIN (tested on Arch).

Checklist

1. Host DNS is correct (/etc/resolv.conf) and does not contain any invalid nameservers
2. Ensure DNS resolves correctly (dig google.com @ipaddress.from.resolvconf.here)
3. Ensure Docker container has same config as host docker run -it <your-image> cat /etc/resolv.conf

Solution

1. Allow docker network interface through firewall firewall-cmd --permanent --zone=trusted --change-interface=docker0
2. Reload firewall firewall-cmd --reload
3. Restart firewall service systemctl restart firewalld
4. Restart network (I use NetworkManager) systemctl restart NetworkManager
5. Kill all the Docker things docker system prune --all --force
6. Restart Docker systemctl restart docker
7. Try ping on image docker run -it <your-image> cat /etc/resolv.conf

Example test: docker run busybox ping -c 3 google.com

Nuclear Solution

If all else fails try stopping firewalld altogether systemctl stop firewalld