CoreDNS

Luke Hebert

- 2 minutes read - 415 words

Setting up a dedicated DNS server with CoreDNS is one of the fastest ways to get reliable name resolution across a small network. You download a single binary, point it at your /etc/hosts file, and you have a working DNS server on port 53. The process also highlights how CoreDNS extends beyond static mappings through its plugin system, including a Kubernetes plugin for cluster-aware resolution.

Prerequisites

From the previous lecture, you should already understand:

  • Why a DNS server is needed (managing name resolution across many hostnames and IPs).
  • How to configure client hosts to point to a DNS server.

Here, you will configure the DNS server itself.

Getting CoreDNS

CoreDNS binaries are available from the GitHub releases page or as a Docker image. We will use the traditional binary approach:

# Download the binary
curl -LO https://github.com/coredns/coredns/releases/latest/download/coredns_linux_amd64

# Make it executable
chmod +x coredns_linux_amd64

# (Optional) Move it to a standard location
sudo mv coredns_linux_amd64 /usr/local/bin/coredns

Exported image

Starting the DNS Server

Run the executable to start the server:

coredns

By default, CoreDNS listens on port 53, the standard port for DNS.

Note

At this point the server is running, but no IP-to-hostname mappings have been defined yet.

Configuring IP-to-Hostname Mappings

Step 1 - Populate /etc/hosts

Add all the desired entries to the DNS server’s /etc/hosts file:

# /etc/hosts
192.168.1.10    web01.example.com
192.168.1.11    db01.example.com
192.168.1.12    cache01.example.com

Step 2 - Create a Corefile

CoreDNS loads its configuration from a file named Corefile. A minimal configuration that instructs CoreDNS to read mappings from /etc/hosts looks like this:

.:53 {
    hosts /etc/hosts
}
TokenMeaning
.:53Listen on all interfaces (.) on port 53
hosts /etc/hostsUse the hosts plugin to resolve names from the specified file

Step 3 - Restart CoreDNS

coredns -conf /path/to/Corefile

CoreDNS now picks up the IPs and names from /etc/hosts and serves them to any client that queries it.

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Beyond /etc/hosts: CoreDNS Plugins

CoreDNS is highly extensible. In addition to the hosts plugin shown above, it supports many other plugins for different data sources and behaviours. Notably, it includes a Kubernetes plugin that dynamically resolves service names within a cluster.

Further Reading

Key Takeaways

  1. CoreDNS is a lightweight, plugin-based DNS server.
  2. It listens on port 53 by default.
  3. The Corefile is the single configuration file that defines behaviour.
  4. The hosts plugin lets you reuse an existing /etc/hosts file as your zone data.
  5. For dynamic or cluster-aware resolution, CoreDNS’s Kubernetes plugin is the go-to option.