### 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")

// IngressClassSpec provides information about the class of an Ingress.
message IngressClassSpec {
  // controller refers to the name of the controller that should handle this
  // class. This allows for different "flavors" that are controlled by the
  // same controller. For example, you may have different parameters for the
  // same implementing controller. This should be specified as a
  // domain-prefixed path no more than 250 characters in length, e.g.

		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()

  // where "pod-specific-string" is managed by the StatefulSet controller.
  optional string serviceName = 5;

  // podManagementPolicy controls how pods are created during initial scale up,
  // when replacing pods on nodes, or when scaling down. The default policy is
  // `OrderedReady`, where pods are created in increasing order (pod-0, then
  // pod-1, etc) and the controller will wait until each pod is ready before

  //
  // 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

  //   Requests for this signer are never auto-approved by kube-controller-manager, can be issued by the "csrsigning" controller in kube-controller-manager.
  //  2. "kubernetes.io/kube-apiserver-client-kubelet": issues client certificates that kubelets use to authenticate to kube-apiserver.

  // 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.

// IngressClassSpec provides information about the class of an Ingress.
message IngressClassSpec {
  // controller refers to the name of the controller that should handle this
  // class. This allows for different "flavors" that are controlled by the
  // same controller. For example, you may have different parameters for the
  // same implementing controller. This should be specified as a
  // domain-prefixed path no more than 250 characters in length, e.g.

{
   "description": "Generic dashboard for controller-runtime based processes\n(https://github.com/kubernetes-sigs/controller-runtime)\n",
   "graphTooltip": 1,
   "panels": [
      {
         "collapsed": false,
         "gridPos": {
            "h": 1,
            "w": 24,
            "x": 0,
            "y": 0
         },
         "id": 1,
         "panels": [ ],
         "title": "Process",
         "type": "row"
      },

`IstioOperatorSpec` has pass-through fields to the Helm values.yaml API, but these are additionally validated through
a [schema](../operator/pkg/apis/istio/v1alpha1/values_types.proto).
1. [Controller](#k8s-controller) code. The code comprises the K8s listener, webhook and logic for reconciling the cluster
to an `IstioOperatorSpec` CR.
1. [Manifest creation](#manifest-creation) code. User settings are overlaid on top of the