Learning CoreDNS

Chapter 9. Building a Custom Server

One of the best things about CoreDNS is how easy it is to customize and add new plug-ins. Because of this, there are a wide variety of external plug-ins available. By “external,” we mean not part of the standard CoreDNS build or repository, and often not even part of the CoreDNS GitHub organization. To utilize external plug-ins, you need to rebuild CoreDNS. Plug-ins are not loaded dynamically, but are instead compiled in at build time.

The CoreDNS code is also structured to make it easy to use as a library. This means that you can create your own main routine and treat the entire CoreDNS code as a library. This chapter covers both of these options.

Compiling CoreDNS with an External Plug-in

The simplest way to build a custom CoreDNS with an external plug-in is to modify only the plugin.cfg file and rebuild CoreDNS. This uses the standard CoreDNS main routine. Your binary will behave exactly like an ordinary CoreDNS, except it will include the additional plug-in and its directives.

You do not need to be a Go developer to build custom versions of CoreDNS, but you will need a machine that’s set up for doing Go builds. If you have Docker up and running, you can get away with just that. Otherwise, you will need Go 1.12 or later, Git, and Make.

First, let’s look at building CoreDNS with only Docker. The examples here will use a Linux machine, but you can also build CoreDNS on Windows.

Building Using Docker

When using Docker, you must first download ...