Learning CoreDNS

Chapter 1. Introduction

This book is about CoreDNS, a new DNS server that’s been designed to work well with containers, such as Linux and Docker containers, and especially well in environments managed by Kubernetes, the popular container orchestration system.

This first chapter explains CoreDNS’s raison d'être, and how it differs from other DNS servers, including its limitations. The chapter also covers a little of the history of CoreDNS, such as its relationship to the Cloud Native Computing Foundation.

What Is CoreDNS?

CoreDNS is DNS server software that’s often used to support the service discovery function in containerized environments, particularly those managed by Kubernetes. Miek Gieben wrote the original version of CoreDNS in 2016. He’d previously written a DNS server called SkyDNS and a popular library of DNS functions in the Go language called Go DNS. Like its successor, CoreDNS, SkyDNS’s main purpose was to support service discovery.  But Miek admired the architecture of a Go-based web server called Caddy, so he forked Caddy to create CoreDNS. CoreDNS thus inherited the major advantages of Caddy: its simple configuration syntax, its powerful plug-in-based architecture, and its foundation in Go.

Compared to the syntax of, say, BIND’s configuration file, CoreDNS’s Corefile, as it’s called, is refreshingly simple. The Corefile for a basic CoreDNS-based DNS server is often just a few lines long and—relatively speaking—easy to read.

CoreDNS uses plug-ins to provide DNS ...