Controller-Runtime

import (
    "context"

    ctrl "sigs.k8s.io/controller-runtime"
    "sigs.k8s.io/controller-runtime/pkg/client"
    "sigs.k8s.io/controller-runtime/pkg/manager"
    "sigs.k8s.io/controller-runtime/pkg/reconcile"
    "sigs.k8s.io/controller-runtime/pkg/builder"
    "sigs.k8s.io/controller-runtime/pkg/log"
    "k8s.io/apimachinery/pkg/runtime/schema"
)

package main

import (
    "context"
    "fmt"

    corev1 "k8s.io/api/core/v1"
    "k8s.io/apimachinery/pkg/runtime"
    ctrl "sigs.k8s.io/controller-runtime"
    "sigs.k8s.io/controller-runtime/pkg/client"
    "sigs.k8s.io/controller-runtime/pkg/manager"
    "sigs.k8s.io/controller-runtime/pkg/reconcile"
)

// Define a reconciler
type PodReconciler struct {
    client.Client
    Scheme *runtime.Scheme
}

func (r *PodReconciler) Reconcile(ctx context.Context, req reconcile.Request) (reconcile.Result, error) {
    // Fetch the Pod
    var pod corev1.Pod
    if err := r.Get(ctx, req.NamespacedName, &pod); err != nil {
        return reconcile.Result{}, client.IgnoreNotFound(err)
    }

    // Implement reconciliation logic
    fmt.Printf("Reconciling Pod: %s/%s\n", pod.Namespace, pod.Name)

    return reconcile.Result{}, nil
}

func main() {
    // Create a manager
    mgr, err := ctrl.NewManager(ctrl.GetConfigOrDie(), manager.Options{})
    if err != nil {
        panic(err)
    }

    // Create and register a controller
    if err := ctrl.NewControllerManagedBy(mgr).
        For(&corev1.Pod{}).
        Complete(&PodReconciler{
            Client: mgr.GetClient(),
            Scheme: mgr.GetScheme(),
        }); err != nil {
        panic(err)
    }

    // Start the manager
    if err := mgr.Start(ctrl.SetupSignalHandler()); err != nil {
        panic(err)
    }
}

// Manager is the central component for managing controllers
type Manager interface {
    cluster.Cluster
    Add(Runnable) error
    Elected() <-chan struct{}
    AddMetricsServerExtraHandler(path string, handler http.Handler) error
    AddHealthzCheck(name string, check healthz.Checker) error
    AddReadyzCheck(name string, check healthz.Checker) error
    Start(ctx context.Context) error
    GetWebhookServer() webhook.Server
    GetLogger() logr.Logger
    GetControllerOptions() config.Controller
}

// Create a new manager
func New(config *rest.Config, options Options) (Manager, error)

// Controller implements a Kubernetes API by responding to events
type Controller interface {
    reconcile.Reconciler
    Watch(src source.Source) error
    Start(ctx context.Context) error
    GetLogger() logr.Logger
}

// Create a new controller
func New(name string, mgr manager.Manager, options Options) (Controller, error)

// Reconciler is the core reconciliation interface
type Reconciler interface {
    Reconcile(context.Context, Request) (Result, error)
}

// Request contains the information necessary to reconcile a Kubernetes object
type Request struct {
    types.NamespacedName
}

// Result contains the result of a Reconciler invocation
type Result struct {
    RequeueAfter time.Duration
}

// Client knows how to perform CRUD operations on Kubernetes objects
type Client interface {
    Reader
    Writer
    StatusClient
    SubResourceClientConstructor
    Scheme() *runtime.Scheme
    RESTMapper() meta.RESTMapper
    GroupVersionKindFor(obj runtime.Object) (schema.GroupVersionKind, error)
    IsObjectNamespaced(obj runtime.Object) (bool, error)
}

// Reader knows how to read and list Kubernetes objects
type Reader interface {
    Get(ctx context.Context, key ObjectKey, obj Object, opts ...GetOption) error
    List(ctx context.Context, list ObjectList, opts ...ListOption) error
}

// Writer knows how to create, delete, update and patch Kubernetes objects
type Writer interface {
    Create(ctx context.Context, obj Object, opts ...CreateOption) error
    Delete(ctx context.Context, obj Object, opts ...DeleteOption) error
    Update(ctx context.Context, obj Object, opts ...UpdateOption) error
    Patch(ctx context.Context, obj Object, patch Patch, opts ...PatchOption) error
    Apply(ctx context.Context, obj runtime.ApplyConfiguration, opts ...ApplyOption) error
    DeleteAllOf(ctx context.Context, obj Object, opts ...DeleteAllOfOption) error
}

// Cache knows how to load Kubernetes objects and fetch informers
type Cache interface {
    client.Reader
    Informers
}

// Informers knows how to create or fetch informers for different GVKs
type Informers interface {
    GetInformer(ctx context.Context, obj client.Object, opts ...InformerGetOption) (Informer, error)
    GetInformerForKind(ctx context.Context, gvk schema.GroupVersionKind, opts ...InformerGetOption) (Informer, error)
    RemoveInformer(ctx context.Context, obj client.Object) error
    Start(ctx context.Context) error
    WaitForCacheSync(ctx context.Context) bool
    client.FieldIndexer
}

// Builder builds a Controller
type Builder struct {
    // Has unexported fields
}

// ControllerManagedBy returns a new controller builder that will be started by the provided Manager
func ControllerManagedBy(m manager.Manager) *Builder

// For defines the type of Object being reconciled
func (blder *Builder) For(object client.Object, opts ...ForOption) *Builder

// Owns defines types of Objects being generated by the controller
func (blder *Builder) Owns(object client.Object, opts ...OwnsOption) *Builder

// Watches watches arbitrary objects and enqueues reconcile requests
func (blder *Builder) Watches(
    object client.Object,
    eventHandler handler.EventHandler,
    opts ...WatchesOption,
) *Builder

// WithEventFilter sets predicates to filter events before enqueuing
func (blder *Builder) WithEventFilter(p predicate.Predicate) *Builder

// Complete builds the controller
func (blder *Builder) Complete(r reconcile.Reconciler) error

// EventHandler enqueues reconcile.Requests in response to events
type EventHandler interface {
    Create(context.Context, event.CreateEvent, workqueue.RateLimitingInterface)
    Update(context.Context, event.UpdateEvent, workqueue.RateLimitingInterface)
    Delete(context.Context, event.DeleteEvent, workqueue.RateLimitingInterface)
    Generic(context.Context, event.GenericEvent, workqueue.RateLimitingInterface)
}

// Predicate filters events before they are provided to EventHandlers
type Predicate interface {
    Create(event.CreateEvent) bool
    Delete(event.DeleteEvent) bool
    Update(event.UpdateEvent) bool
    Generic(event.GenericEvent) bool
}

// Source is a source of events for a Controller
type Source interface {
    Start(context.Context, workqueue.RateLimitingInterface) error
}

// Server manages webhook registration and serving
type Server interface {
    NeedLeaderElection() bool
    Register(path string, hook http.Handler)
    Start(ctx context.Context) error
    StartedChecker() healthz.Checker
    WebhookMux() *http.ServeMux
}

// Handler processes admission requests
type Handler interface {
    Handle(context.Context, Request) Response
}

// CustomValidator validates create, update, and delete operations
type CustomValidator interface {
    ValidateCreate(ctx context.Context, obj runtime.Object) (warnings Warnings, err error)
    ValidateUpdate(ctx context.Context, oldObj, newObj runtime.Object) (warnings Warnings, err error)
    ValidateDelete(ctx context.Context, obj runtime.Object) (warnings Warnings, err error)
}

// CustomDefaulter sets defaults on objects
type CustomDefaulter interface {
    Default(ctx context.Context, obj runtime.Object) error
}

// Environment provides a test control plane with etcd and kube-apiserver
type Environment struct {
    ControlPlane                 controlplane.ControlPlane
    Scheme                       *runtime.Scheme
    Config                       *rest.Config
    CRDInstallOptions            CRDInstallOptions
    WebhookInstallOptions        WebhookInstallOptions
    UseExistingCluster           *bool
    ControlPlaneStartTimeout     time.Duration
    ControlPlaneStopTimeout      time.Duration
    AttachControlPlaneOutput     bool
}

func (te *Environment) Start() (*rest.Config, error)
func (te *Environment) Stop() error

// ClientBuilder builds fake clients for testing
type ClientBuilder struct {
    // Has unexported fields
}

func NewClientBuilder() *ClientBuilder
func (f *ClientBuilder) WithObjects(initObjs ...client.Object) *ClientBuilder
func (f *ClientBuilder) WithScheme(scheme *runtime.Scheme) *ClientBuilder
func (f *ClientBuilder) Build() client.WithWatch

// Logging functions
func SetLogger(l logr.Logger)
func FromContext(ctx context.Context, keysAndValues ...interface{}) logr.Logger
func IntoContext(ctx context.Context, log logr.Logger) context.Context

// Metrics registry
var Registry RegistererGatherer = prometheus.NewRegistry()

// Health check types
type Checker func(req *http.Request) error
var Ping Checker = func(_ *http.Request) error { return nil }

// Leader election options
type Options struct {
    LeaderElection              bool
    LeaderElectionResourceLock  string
    LeaderElectionNamespace     string
    LeaderElectionID            string
    RenewDeadline               time.Duration
    LeaderLabels                map[string]string
}

// Finalizer operations
func AddFinalizer(o client.Object, finalizer string) (finalizersUpdated bool)
func RemoveFinalizer(o client.Object, finalizer string) (finalizersUpdated bool)
func ContainsFinalizer(o client.Object, finalizer string) bool

// Owner reference management
func SetControllerReference(owner, controlled metav1.Object, scheme *runtime.Scheme, opts ...OwnerReferenceOption) error
func SetOwnerReference(owner, object metav1.Object, scheme *runtime.Scheme, opts ...OwnerReferenceOption) error

// Scheme building
type Builder struct {
    GroupVersion schema.GroupVersion
    runtime.SchemeBuilder
}

func (bld *Builder) Register(object ...runtime.Object) *Builder
func (bld *Builder) Build() (*runtime.Scheme, error)