A custom Kubernetes controller manages custom resources within a Kubernetes cluster, allowing for extended functionalities and custom automation.
Step-by-Step Guide
Define Custom Resource:
Define a custom resource definition (CRD) in a YAML file.
apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
name: myresources.mydomain.com
spec:
group: mydomain.com
versions:
- name: v1
served: true
storage: true
schema:
openAPIV3Schema:
type: object
properties:
spec:
type: object
properties:
size:
type: integer
scope: Namespaced
names:
plural: myresources
singular: myresource
kind: MyResource
shortNames:
- mr
Generate Clientset:
Use kubebuilder to generate clientset, informers, and listers for your CRD.
kubebuilder init --domain mydomain.com
kubebuilder create api --group mydomain --version v1 --kind MyResource
make
Implement the Controller:
Write the logic for your custom controller.
import (
"context"
"sigs.k8s.io/controller-runtime/pkg/client"
"sigs.k8s.io/controller-runtime/pkg/controller"
"sigs.k8s.io/controller-runtime/pkg/manager"
)
type MyResourceReconciler struct {
client.Client
}
func (r *MyResourceReconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
var myresource mydomainv1.MyResource
if err := r.Get(ctx, req.NamespacedName, &myresource); err != nil {
return ctrl.Result{}, client.IgnoreNotFound(err)
}
// Your reconciliation logic here
return ctrl.Result{}, nil
}
func main() {
mgr, err := ctrl.NewManager(ctrl.GetConfigOrDie(), ctrl.Options{})
if err != nil {
log.Fatal(err)
}
if err := ctrl.NewControllerManagedBy(mgr).
For(&mydomainv1.MyResource{}).
Complete(&MyResourceReconciler{mgr.GetClient()}); err != nil {
log.Fatal(err)
}
log.Fatal(mgr.Start(ctrl.SetupSignalHandler()))
}
Deploy the Controller:
Build and deploy your controller to the Kubernetes cluster.
make docker-build docker-push IMG=<your-image>
make deploy IMG=<your-image>
- Apply CR Instances: Create instances of your custom resource.
apiVersion: mydomain.com/v1
kind: MyResource
metadata:
name: example-myresource
spec:
size: 3