🌱examples-builtin: Refactor controller setup to use builder pattern

[s-z-z]

What

Refactors builtin example: main.go to use controller-runtime builder pattern (ctrl.NewControllerManagedBy) instead of controller.New for controller setup, consolidating ReplicaSet and Pod watches.

Why

The builder pattern is the recommended approach for Kubernetes controllers, improving code readability, maintainability, and alignment with community practices.

Impact

No functional changes. Enhances code clarity and consistency with other projects.

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[s-z-z]

I test it, and it works correctly.

here is the result

command line operation

xdev➜  k --kubeconfig /tmp/k8s_test_framework_1613410604/4021304843.kubecfg get rs
No resources found in default namespace.

xdev➜  cat rs.yaml
apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: frigate-replicaset
  namespace: default
  labels:
    app: frigate
spec:
  replicas: 3
  selector:
    matchLabels:
      app: frigate
  template:
    metadata:
      labels:
        app: frigate
    spec:
      containers:
        - name: frigate
          image: nginx:1.14.2#

xdev➜  k --kubeconfig /tmp/k8s_test_framework_1613410604/4021304843.kubecfg apply -f rs.yaml
replicaset.apps/frigate-replicaset created

xdev➜  k --kubeconfig /tmp/k8s_test_framework_1613410604/4021304843.kubecfg get rs frigate-replicaset -o yaml
apiVersion: apps/v1
kind: ReplicaSet
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"apps/v1","kind":"ReplicaSet","metadata":{"annotations":{},"labels":{"app":"frigate"},"name":"frigate-replicaset","namespace":"default"},"spec":{"replicas":3,"selector":{"matchLabels":{"app":"frigate"}},"template":{"metadata":{"labels":{"app":"frigate"}},"spec":{"containers":[{"image":"nginx:1.14.2","name":"frigate"}]}}}}
  creationTimestamp: "2025-07-29T10:53:09Z"
  generation: 1
  labels:
    app: frigate
    hello: world
  name: frigate-replicaset
  namespace: default
  resourceVersion: "212"
  uid: ba2d8168-ea52-48e4-88c5-3b062246377e
spec:
  replicas: 3
  selector:
    matchLabels:
      app: frigate
  template:
    metadata:
      creationTimestamp: null
      labels:
        app: frigate
    spec:
      containers:
      - image: nginx:1.14.2
        imagePullPolicy: IfNotPresent
        name: frigate
        resources: {}
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File
      dnsPolicy: ClusterFirst
      restartPolicy: Always
      schedulerName: default-scheduler
      securityContext: {}
      terminationGracePeriodSeconds: 30
status:
  replicas: 0

the rs got the label hello: world after create.

controller log

KUBEBUILDER_ASSETS="/root/envtest/k8s/1.33.0-linux-amd64" go run ./cmd/...
{"level":"info","ts":"2025-07-29T18:52:18+08:00","logger":"entrypoint","msg":"setting up manager"}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","logger":"entrypoint","msg":"Setting up controller"}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","logger":"controller-runtime.builder","msg":"Registering a mutating webhook","GVK":"/v1, Kind=Pod","path":"/mutate--v1-pod"}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","logger":"controller-runtime.webhook","msg":"Registering webhook","path":"/mutate--v1-pod"}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","logger":"controller-runtime.builder","msg":"Registering a validating webhook","GVK":"/v1, Kind=Pod","path":"/validate--v1-pod"}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","logger":"controller-runtime.webhook","msg":"Registering webhook","path":"/validate--v1-pod"}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","logger":"entrypoint","msg":"starting manager"}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","logger":"controller-runtime.metrics","msg":"Starting metrics server"}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","logger":"controller-runtime.webhook","msg":"Starting webhook server"}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","logger":"controller-runtime.metrics","msg":"Serving metrics server","bindAddress":":8080","secure":false}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","logger":"controller-runtime.certwatcher","msg":"Updated current TLS certificate"}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","logger":"controller-runtime.webhook","msg":"Serving webhook server","host":"","port":9443}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","msg":"Starting EventSource","controller":"foo-controller","source":"kind source: *v1.Pod"}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","logger":"controller-runtime.certwatcher","msg":"Starting certificate poll+watcher","interval":10}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","msg":"Starting EventSource","controller":"foo-controller","source":"kind source: *v1.ReplicaSet"}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","msg":"Starting Controller","controller":"foo-controller"}
{"level":"info","ts":"2025-07-29T18:52:22+08:00","msg":"Starting workers","controller":"foo-controller","worker count":1}
{"level":"info","ts":"2025-07-29T18:53:09+08:00","msg":"Reconciling ReplicaSet","controller":"foo-controller","namespace":"default","name":"frigate-replicaset","reconcileID":"8cfd1326-b14b-4c51-8cd9-12fcdd3577f8","container name":"frigate"}
{"level":"info","ts":"2025-07-29T18:53:09+08:00","msg":"Reconciling ReplicaSet","controller":"foo-controller","namespace":"default","name":"frigate-replicaset","reconcileID":"b303c793-7791-4454-b42e-f1f9fca1b238","container name":"frigate"}

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: d9614a9e1e60311c58ac2c07f5691c33c0914e5e

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alvaroaleman, s-z-z

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