Too many tutorials start out with some really contrived setup, or some toy application that gets the basics across, and then stalls out on the more complicated stuff. Instead, this tutorial should take you through (almost) the full gamut of complexity with Kubebuilder, starting off simple and building up to something pretty full-featured.
Let's pretend (and sure, this is a teensy bit contrived) that we've finally gotten tired of the maintenance burden of the non-Kubebuilder implementation of the CronJob controller in Kubernetes, and we'd like to rewrite it using Kubebuilder.
The job (no pun intended) of the CronJob controller is to run one-off tasks on the Kubernetes cluster at regular intervals. It does this by building on top of the Job controller, whose task is to run one-off tasks once, seeing them to completion.
Instead of trying to tackle rewriting the Job controller as well, we'll use this as an opportunity to see how to interact with external types.
Note that most of this tutorial is generated from literate Go files that live in the book source directory: docs/book/src/cronjob-tutorial/testdata. The full, runnable project lives in project, while intermediate files live directly under the testdata directory.
As covered in the quick start, we'll need to scaffold out a new project. Make sure you've installed Kubebuilder, then scaffold out a new project:
# create a project directory, and then run the init command.
mkdir project
cd project
# we'll use a domain of tutorial.kubebuilder.io,
# so all API groups will be <group>.tutorial.kubebuilder.io.
kubebuilder init --domain tutorial.kubebuilder.io --repo tutorial.kubebuilder.io/projectYour project's name defaults to that of your current working directory.
You can pass --project-name=<dns1123-label-string> to set a different project name.
Now that we've got a project in place, let's take a look at what Kubebuilder has scaffolded for us so far...
If your project is initialized within GOPATH, the implicitly called go mod init will interpolate the module path for you.
Otherwise --repo=<module path> must be set.
Read the Go modules blogpost if unfamiliar with the module system.