Every journey needs a start, every program a main

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Our package starts out with some basic imports. Particularly:

  • The core controller-runtime library
  • The default controller-runtime logging, Zap (more on that a bit later)

package main

import (

    _ "k8s.io/client-go/plugin/pkg/client/auth/gcp"
    ctrl "sigs.k8s.io/controller-runtime"
    // +kubebuilder:scaffold:imports

Every set of controllers needs a Scheme, which provides mappings between Kinds and their corresponding Go types. We’ll take a bit more about Kinds when we write our API definition, so just keep this in mind for later.

var (
    scheme   = runtime.NewScheme()
    setupLog = ctrl.Log.WithName("setup")

func init() {

    // +kubebuilder:scaffold:scheme

At this point, our main function is fairly simple:

  • We set up some basic flags for metrics.

  • We instantiate a manager, which keeps track of running all of our controllers, as well as setting up shared caches and clients to the API server (notice we tell the manager about our Scheme).

  • We run our manager, which in turn runs all of our controllers and webhooks. The manager is set up to run until it receives a graceful shutdown signal. This way, when we’re running on Kubernetes, we behave nicely with graceful pod termination.

While we don’t have anything to run just yet, remember where that +kubebuilder:scaffold:builder comment is -- things’ll get interesting there soon.

func main() {
    var metricsAddr string
    flag.StringVar(&metricsAddr, "metrics-addr", ":8080", "The address the metric endpoint binds to.")


    mgr, err := ctrl.NewManager(ctrl.GetConfigOrDie(), ctrl.Options{Scheme: scheme, MetricsBindAddress: metricsAddr})
    if err != nil {
        setupLog.Error(err, "unable to start manager")

    // +kubebuilder:scaffold:builder

    setupLog.Info("starting manager")
    if err := mgr.Start(ctrl.SetupSignalHandler()); err != nil {
        setupLog.Error(err, "problem running manager")

With that out of the way, we can get on to scaffolding our API!