## 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.

  // 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.

`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

  value other than `kubernetes.io/job-controller` - are skipped by the job controller, and their
  reconciliation is delegated to an external controller, indicated by the value of the field. Jobs that
  don't have this field at all, or where the field value is the reserved string `kubernetes.io/job-controller`,

  // +optional
  optional EventSeries series = 3;

  // reportingController is the name of the controller that emitted this Event, e.g. `kubernetes.io/kubelet`.
  // This field cannot be empty for new Events.
  // +optional
  optional string reportingController = 4;

  // reportingInstance is the ID of the controller instance, e.g. `kubelet-xyzf`.
  // This field cannot be empty for new Events and it can have at most 128 characters.

### kubectl delete

  // +optional
  optional string reason = 2;

  // AuditAnnotations will be added to the attributes object of the
  // admission controller request using 'AddAnnotation'.  The keys should
  // be prefix-less (i.e., the admission controller will add an
  // appropriate prefix).
  // +optional
  map<string, string> auditAnnotations = 3;

// 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.

  // processed by the API server eviction subresource handler but has not
  // yet been observed by the PodDisruptionBudget controller.
  // A pod will be in this map from the time when the API server processed the
  // eviction request to the time when the pod is seen by PDB controller
  // as having been marked for deletion (or after a timeout). The key in the map is the name of the pod

  * You can find the PodSpec tolerations that were created as annotations (if any) in a controller definition by doing `kubectl get <controller kind> <controller name> -o yaml` and looking for the "Annotation" section with the annotation key `scheduler.alpha.kubernetes.io/tolerations` (This will work whether you are running Kubernetes 1.5 or 1.6).