Simple Custom Controller

In this project we create a k8s CRD (Custom Resource Defintion) and a controller for it. The controller follows the pattern shown in kubernetes/sample-controller.

The CRD (Custom Resource Definition)

type Book struct {
	metav1.TypeMeta   `json:",inline"`
	metav1.ObjectMeta `json:"metadata,omitempty"`

	Spec   BookSpec   `json:"spec"`
	Status BookStatus `json:"status,omitempty"`
}

type BookSpec struct {
	DeploymentName string           `json:"deploymentName"`
	Replicas       *int32           `json:"replicas"`
	Container      corev1.Container `json:"container"`
}

type BookStatus struct {
	AvailableReplicas int32 `json:"availableReplicas"`
}

type BookList struct {
	metav1.TypeMeta `json:",inline"`
	metav1.ListMeta `json:"metadata"`

	Items []Book `json:"items"`
}

And, the auto-generated (by controller-gen) yaml file can be found at manifests/simplecustomcontroller.crd.com_books.yaml

The CR (Custom Resource)

So, a valid CR for our CRD is-

apiVersion: simplecustomcontroller.crd.com/v1
kind: Book
metadata:
  name: example-book
spec:
  deploymentName: example-book
  replicas: 1
  container:
    name: book-store
    image: shiponcs/book-store-api-server
    ports:
      - containerPort: 8080

What does this Controller do?

The controller registers a Book type Custom Resource in k8s api-server and manage its objects. If we create a Custom Resource of Kind: Book, the controller will take the following actions

• Create a deployment to create pods with container value given in the applied Book resource
• Create Service for the deployment
• Create a deployment to deploy Envoy with HTTP proxy configuration
• Create LoadBalancer type service for Envoy
• Take appropriate action on receiving events from api-server
• Periodically sync the current state with desired state

Relevant

The controller deploys this- shiponcs/golang-rest-api-server.

Install using Helm

helm install scc charts/ --namespace scc --create-namespace --set fullnameOverride=book-controller