DEV Community

Cover image for How to Add Domains and IP Addresses to Docker Containers
Berk
Berk

Posted on • Originally published at burakberk.dev

How to Add Domains and IP Addresses to Docker Containers

#dnsamsq #hosts #domain #docker

Overview

Docker users often face challenges with custom domain and IP address mappings in their containers. The inability of containers to read the host machine's /etc/hosts file creates significant obstacles.

In this practical guide, we'll tackle this common Docker networking challenge: how to make containers resolve custom domains and IP addresses without modifying each container individually.

We'll cover two methods: integrating dnsmasq with NetworkManager and configuring dnsmasq without NetworkManager. By the end of this post, you'll be able to easily manage custom domain resolutions in your containers.

By the end of this post, you'll be able to:

  • Easily add custom domain resolutions to all your Docker containers
  • Streamline your development and testing workflows
  • Avoid the headache of managing /etc/hosts files for each container

Table of Contents

  1. Install Dnsmasq
  2. Configure Dnsmasq
    1. Dnsmasq Standalone Usage
    2. Dnsmasq with NetworkManager
  3. Configure Docker
  4. Add Test Domain Names to /etc/hosts
  5. Test the Custom Domain Names

Install Dnsmasq

  • Make sure dnsmasq is installed. 
which dnsmasq
Enter fullscreen mode Exit fullscreen mode
  • If not installed, install it 
# For Debian / Ubuntu
sudo apt install dnsmasq

# For RHEL / CentOS / Fedora
sudo dnf install dnsmasq
Enter fullscreen mode Exit fullscreen mode

Configure Dnsmasq

Dnsmasq Standalone Usage

In this section, we'll configure dnsmasq if you are not using NetworkManager.

  • Create a new configuration file for dnsmasq: 
sudo vim /etc/dnsmasq.conf
Enter fullscreen mode Exit fullscreen mode
  • Add the following configuration options: 
# Listen on the Docker bridge interface
interface=docker0

# Specify a default DNS server to forward queries
server=8.8.8.8  # Example: Google DNS
Enter fullscreen mode Exit fullscreen mode
  • Start the dnsmasq service and enable it to run on boot: 
sudo systemctl stop dnsmasq && \
sudo systemctl enable --now dnsmasq && \
sudo systemctl status dnsmasq
Enter fullscreen mode Exit fullscreen mode

Dnsmasq with NetworkManager

If you are using NetworkManager, you can use dnsmasq as its plugin.

  • Open NetworkManager main configuration file with an text editor: 
sudo vim /etc/NetworkManager/NetworkManager.conf
Enter fullscreen mode Exit fullscreen mode
  • Find the [main] section and add dns=dnsmasq 
[main]
dns=dnsmasq
Enter fullscreen mode Exit fullscreen mode
  • Create dnsmasq configuration file in the config daemon directory. 
sudo vim /etc/NetworkManager/dnsmasq.d/split-dns.conf
Enter fullscreen mode Exit fullscreen mode 
# Listen on the Docker bridge interface
interface=docker0

# Specify a default DNS server to forward queries
server=8.8.8.8  # Example: Google DNS
Enter fullscreen mode Exit fullscreen mode
  • Check if NetworkManager is running without no problem. 
sudo systemctl restart NetworkManager && \
sleep 5 && \
sudo systemctl status NetworkManager
Enter fullscreen mode Exit fullscreen mode
  • If there are problems, check the NetworkManager logs. 
journalctl -u NetworkManager -r
Enter fullscreen mode Exit fullscreen mode

Configure Docker

  • Check the IP address of the docker0. 
ip a show docker0
Enter fullscreen mode Exit fullscreen mode 
4: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
    link/ether 02:42:a9:72:e1:3a brd ff:ff:ff:ff:ff:ff
    inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
       valid_lft forever preferred_lft forever
    inet6 fe80::42:a9ff:fe72:e13a/64 scope link
       valid_lft forever preferred_lft forever
Enter fullscreen mode Exit fullscreen mode
  • Configure Docker to use the Dnsmasq 
sudo vim /etc/docker/daemon.json
Enter fullscreen mode Exit fullscreen mode 
{
  "dns": ["172.17.0.1"]
}
Enter fullscreen mode Exit fullscreen mode
  • Restart the docker service 
sudo systemctl restart docker
Enter fullscreen mode Exit fullscreen mode

Add Test Domain Names to /etc/hosts

For testing purposes, add a domain to /etc/hosts.

sudo bash -c "echo '192.168.1.12 nonexisting.example.com' >> /etc/hosts"
Enter fullscreen mode Exit fullscreen mode

Restart the dnsmasq service to get updates.

sudo systemctl restart dnsmasq
Enter fullscreen mode Exit fullscreen mode

Test the Custom Domain Names

In the /etc/hosts file, we defined nonexisting.example.com as 192.168.1.10.

Lets test if the configuration works as expected.

docker run --rm --name dns-test busybox nslookup nonexisting.example.com
Enter fullscreen mode Exit fullscreen mode

The output should be:

Server:     172.17.0.1
Address:    172.17.0.1:53

Non-authoritative answer:

Non-authoritative answer:
Name:   example.com
Address: 192.168.1.10
Enter fullscreen mode Exit fullscreen mode

Viola, you can set any custom domain name in the /etc/hosts file on the host machine and containers will use it by default.

For More

If you like the post, you can head to my personal blog site and read more about DevOps, Linux, system engineering, and self-hosted applications for homelab!

Burak Berk Keskin

Blog of a DevOps & System Engineer

favicon burakberk.dev

Top comments (0)

Read next

limal profile image

Reclaiming free disk space from a private Docker repository

Łukasz Wolnik -

yukaty profile image

Part 3: Implementing Vector Search with Ollama

yukaty -

rakibtweets profile image

Dockerize MERN Application

Rakib Hasan -

ajeetraina profile image

Containerize Rust Application in 2 Minutes using Docker Init

Ajeet Singh Raina -