Example Controller

First example in controller-runtime

Example

1. Run example controller.

   go run example-controller.go
   

   What this controller does:

   1. Read the ReplicaSet
   2. Read the Pods
   3. Set a Label on the ReplicaSet with the Pod count.

2. Create Deployment

   kubectl create deploy test --replicas=3 --image=nginx
   

   You would see some errors, these errors happen because replicaset is updated by replicaset controller according to new Pod's status.

   1.6565476218562e+09     ERROR   controller.replicaset   Reconciler error        {"reconciler group": "apps", "reconciler kind": "ReplicaSet", "name": "test-8499f4f74", "namespace": "default", "error": "Operation cannot be fulfilled on replicasets.apps \"test-8499f4f74\": the object has been modified; please apply your changes to the latest version and try again"}
   sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem
           /Users/nakamasato/.gvm/pkgsets/go1.17.9/global/pkg/mod/sigs.k8s.io/controller-runtime@v0.11.2/pkg/internal/controller/controller.go:266
   sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2.2
           /Users/nakamasato/.gvm/pkgsets/go1.17.9/global/pkg/mod/sigs.k8s.io/controller-runtime@v0.11.2/pkg/internal/controller/controller.go:227
   

3. Check pod-count=3 labels added to the ReplicaSet

   kubectl get rs -o jsonpath='{.items[].metadata.labels}'
   {"app":"test","pod-count":"3","pod-template-hash":"8499f4f74"}
   

4. Clean up

   kubectl delete deploy test