## Writing Controllers

The `controllers` package offers a variety of helpers for writing controllers.
These operate in a similar manner as [`controller-runtime`](https://github.com/kubernetes-sigs/controller-runtime) but are *far* smaller and less abstract.

With a few exceptions, Istio controllers typically are split in two phases: construction and running.

### Controllers overview

Below provides a high level overview of controllers in Istiod. For more information about each controller, consulting the controllers Go docs is recommended.

```mermaid
graph BT
    crd("CRD Watcher")
    subgraph Service Discovery
        ksd("Kubernetes Controller")
        sesd("Service Entry Controller")

		controllers.WithMaxAttempts(5),
	)
	// We only need to handle pods on our node
	s.pods = kclient.NewFiltered[*corev1.Pod](kubeClient, kclient.Filter{FieldSelector: "spec.nodeName=" + NodeName})
	s.pods.AddEventHandler(controllers.FromEventHandler(func(o controllers.Event) {
		s.queue.Add(o)
	}))

	// Namespaces could be anything though, so we watch all of those
	//

		FieldSelector: strings.Join(fieldSelectors, ","),
	})
	c.queue = controllers.NewQueue("repair pods",
		controllers.WithReconciler(c.Reconcile),
		controllers.WithMaxAttempts(5))
	c.pods.AddEventHandler(controllers.ObjectHandler(c.queue.AddObject))

	return c, nil
}

func (c *Controller) Run(stop <-chan struct{}) {
	kube.WaitForCacheSync("repair controller", stop, c.pods.HasSynced)
	c.queue.Run(stop)
	c.pods.ShutdownHandlers()

# ~~~~

# Home page
# GET     /                           controllers.Application.index()
GET         /suggest/get                        controllers.Suggest.get()
GET         /suggest/create/content             controllers.Suggest.createContent()
GET         /suggest/create/suggest/content     controllers.Suggest.createSuggestFromContent()


GET        /                    controllers.Assets.at(path="/public", s="index.html")

// the DaemonSet and StatefulSet controllers for update and rollback, this object is beta. However,
// it may be subject to name and representation changes in future releases, and clients should not
// depend on its stability. It is primarily for internal use by controllers.
message ControllerRevision {
  // Standard object's metadata.

  //
  // More completion modes can be added in the future.
  // If the Job controller observes a mode that it doesn't recognize, which
  // is possible during upgrades due to version skew, the controller
  // skips updates for the Job.
  // +optional
  optional string completionMode = 9;

  // suspend specifies whether the Job controller should create Pods or not. If

  // replicas is the number of Pods created by the StatefulSet controller.
  optional int32 replicas = 2;

  // readyReplicas is the number of pods created by this StatefulSet controller with a Ready Condition.
  optional int32 readyReplicas = 3;

  // currentReplicas is the number of Pods created by the StatefulSet controller from the StatefulSet version
  // indicated by currentRevision.

package controllers;

import models.*;
import org.codelibs.fess.suggest.request.suggest.SuggestResponse;
import org.elasticsearch.common.xcontent.XContentBuilder;
import org.elasticsearch.common.xcontent.json.JsonXContent;
import play.Logger;
import play.mvc.Controller;
import play.mvc.Result;

import java.util.Map;

public class Suggest extends Controller {
    public static Result get() {

import components.*;
import controllers.*;
import org.codelibs.elasticsearch.runner.ElasticsearchClusterRunner;
import org.codelibs.fess.suggest.Suggester;
import play.Application;
import play.GlobalSettings;
import play.Logger;

import static org.codelibs.elasticsearch.runner.ElasticsearchClusterRunner.newConfigs;

public class Global extends GlobalSettings {
    @Override
    public void onStart(Application var1) {