DNS resolution in Docker containers with Ubuntu Artful on AWS

This post is solution to a problem I discovered - so I hope others will find it useful.

Spinning up AWS Ubuntu Zesty - 17.04 - images with Docker installed was straight forward with Ansible and Terraform , but then arrived Ubuntu Artful - 17.10 , and the containers spun up could not resolve DNS, regardless of which version of Docker I installed.

After a lot of testing , it appeared to me that the host computer was passing through the wrong DNS server entry into resolv.conf within the container - so it would never work.

The Solution:

With systemd and docker, the preferred way to change a daemon setting is to create a new file in /etc/docker called daemon.json.

In that file add the following to get it use the AWS VPC default DNS resolver - 10.0.0.2 - like so

{
   "dns": ["10.0.0.2"]
}

Restart the docker daemon , and the containers can now resolve DNS. There may be other ways to resolve this issue, but this works perfectly , and uses methods preferred by the docker community.

I hope this helps others who may run into this problem.

Other settings that can be made in that file can be found here. Dockerd settings documentation