Docker With Custom DNS Server

By configuring your Docker containers to talk to a custom DNS server, you gain more control over how your container look up other services – database, other microservices, etc.,

It turns out Docker networking isn’t completely straight forward. On Linux you can:

  1. Run a DNS server locally, either dnsmasq or devdns
  2. Run your container with --dns 172.17.0.1, the magic IP where your host machine is located
  3. Configure dnsmasq from step 1 via /etc/hosts

Sadly, none of it was easy. The entire thing probably took me three hours.

Install the DNS server was… confusing. I wouldn’t know how to verify if my DNS queries (via the dig command) where answered by the DNS server I configured. I discovered I was talking to a [systemd-resolved][4] instance by guesswork, which prompted me to finally install dnsmasq.

But finally, with dnsmasq running locally, the Docker containers running on my machine can be affected by my configurations in /etc/hosts, which makes integration testing against other services much easier.