Docker container can reach DNS but not resolve hosts

Question

I'm having an interesting problem running docker containers: out of the blue, I'm not able to resolve DNS from within the container.

Here's a rundown:

1. Nothing is resolving; apt-get, pip, one-off ping containers, etc. Running docker run -it --dns=8.8.8.8 ubuntu ping www.google.com results in ping: unknown host www.google.com both with and without the --dns flag.

2. I can reach 8.8.8.8 both from inside and outside the containers. docker run -it ubuntu ping 8.8.8.8 works.

3. I've configured the containers to use both 8.8.8.8, 8.8.8.4, and my local network DNS servers (in various permutations) both by editing /etc/sysconfig/docker to add DOCKER_OPTS="--dns 8.8.8.8 --dns 8.8.8.4" and by setting the --dns 8.8.8.8 flag on the containers at runtime. systemctl restart docker was run between each change.

4. ip_forward is enabled. (see here)

5. I've done a full reset as specified here.

I'm running Fedora 21, docker client version 1.5.0.

Any ideas? I'm at a complete loss as to what's preventing docker from accessing the Internet successfully.

Funeral

Perhaps you should open an issue in the docker issue tracker; github.com/docker/docker/issues. When doing so, please include the relevant information as explained here github.com/docker/docker/blob/master/CONTRIBUTING.md – Belie

Same here with fedora 22. – Carousel

Answer 1

They have fixed the issue in 1.8: https://github.com/docker/docker/issues/13381 Cheers.

Monafo

Could you link to the fix for posterity? – Funeral

Yeah, link was a pain to re-find lol. I really need to start tracking the Q&A of my problems for reference. – Monafo

Answer 2

After all this, a full reboot solved the problem - although, that still doesn't answer what it was.

If anyone knows what the actual cause was, I'm still curious, but for now the problem is gone.

Funeral

I'm having the problem repeatedly, reboot helps but can't be the solution. The problem doesn't just occur with the ubuntu image, but all I've tried. – Carousel

Answer 3

You could install tools like dig inside the docker image to alanyse the issue.

use static hosts in your /etc/hosts file te make apt-get run inside the docker image. add these lines to your hosts file:

213.32.5.7 debian.mirrors.ovh.net
141.76.2.4 ftp.de.debian.org 
217.196.149.233 mirror-conova-security.debian.org
212.211.132.250 lobos.debian.org
212.211.132.250 security.debian.org 
5.153.231.4  http.debian.net 
151.101.12.204 cdn-fastly.deb.debian.org
151.101.12.204 security-cdn.debian.org

Uterine