Docker on Ubuntu: when apt-get update fails

I've been spending some time with Docker, and since digitalocean provides Ubuntu images with Docker already configured, setting up a new droplet and a few containers with my apps has become a matter of minutes.

One of the fist commands you want to run in your Dockerfile is certainly 'apt-get update'. I'm writing this with the hope to save the reader some precious time: if 'apt-get update' fails, you may want to ensure that docker's DNS configuration is complete (and servers are accessible).

In my case this meant simply adding the Google DNS servers in /etc/default/docker:

DOCKER_OPTS="--dns 8.8.8.8 --dns 8.8.4.4"

and restart docker with

sudo service docker restart

This StackOverflow question is related.