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Kubebuilder

https://kubebuilder.io, notably https://kubebuilder.io/quick-start.html, and https://github.com/kubernetes-sigs/kubebuilder.

Install kubebuilder

curl -L -o kubebuilder https://go.kubebuilder.io/dl/latest/$(go env GOOS)/$(go env GOARCH)
chmod +x kubebuilder && sudo mv kubebuilder /usr/local/bin/

kubebuilder
kubebuilder init --help

Quick Start

mkdir learning-kubebuilder && cd learning-kubebuilder
kubebuilder init --domain vorburger.ch --repo github.com/vorburger/learning-kubebuilder --project-name learning-kubebuilder --owner "Michael Vorburger" --component-config true
kubebuilder create api --group learning --kind Foo --version v1

make install
k api-resources | grep foo
make run

cat config/samples/*
k apply -f config/samples/
k get foo foo-sample -o yaml

Stop (Ctrl-C) the make run to clean-up.

Modify Controller

You may want to use your favourite Go IDE of choice instead of a text editor for the following code changes. The web-based Google Cloud Code, or Gitpod, both based on Eclipse Theia, are a great choice. Alternatives include e.g. VS Code, or your favourite TUI editor with LSP support.

  1. edit the controllers/foo_controller.go and change the Reconcile function to look like this:

    log := log.FromContext(ctx)

var foo model.Foo
if err := r.Get(ctx, req.NamespacedName, &foo); err != nil {
    log.Error(err, "Get failed")
    return ctrl.Result{}, client.IgnoreNotFound(err)
}

log.Info("Reconciled")
return ctrl.Result{}, nil

  2. re-run the controller with make run

  3. edit the Foo resource and change its spec.foo from bar to baz (just to "touch" it)

    k edit foo foo-sample

  4. observe how "Reconciled" is logged again

Add status

  1. make a backup of the initial CRD YAML (or use git diff in the step after the next):

    cp config/crd/bases/learning.vorburger.ch_foos.yaml config/crd/bases/learning.vorburger.ch_foos.original.yaml

  2. edit the api/v1/foo_types.go and change the type FooStatus struct to look like this:

    type FooStatus struct {
    Bar string `json:"bar,omitempty"`
}

  3. re-generate the generated CRD YAML, and note how bar got added to status:

    make install
diff config/crd/bases/learning.vorburger.ch_foos.yaml config/crd/bases/learning.vorburger.ch_foos.original.yaml

  4. edit the controllers/foo_controller.go and change the Reconcile function to look like this:

    log := log.FromContext(ctx)

var foo model.Foo
if err := r.Get(ctx, req.NamespacedName, &foo); err != nil {
    log.Error(err, "Get failed")
    return ctrl.Result{}, client.IgnoreNotFound(err)
}

foo.Status.Bar = "hello, " + foo.GetName() + " with spec " + foo.Spec.Foo
if err := r.Status().Update(ctx, &foo); err != nil {
    log.Error(err, "Update failed")
    return ctrl.Result{}, err
}

log.Info("Reconciled")
return ctrl.Result{}, nil

  5. re-run the controller with make run

  6. run k get foo foo-sample -o yaml and notice the new status

  7. edit the Foo resource and change its spec.foo back from baz to bar (just to "touch" it)

    k edit foo foo-sample

  8. re-run k get foo foo-sample -o yaml and notice the updated status