openshift-docs/modules/osdk-golang-implement-controller.adoc

// Module included in the following assemblies:
//
// * operators/operator_sdk/golang/osdk-golang-tutorial.adoc

:_mod-docs-content-type: PROCEDURE
[id="osdk-golang-implement-controller_{context}"]
= Implementing the controller

After creating a new API and controller, you can implement the controller logic.

.Procedure

* For this example, replace the generated controller file `controllers/memcached_controller.go` with following example implementation:
+
.Example `memcached_controller.go`
[%collapsible]
====
[source,golang]
----
/*
Copyright 2020.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package controllers

import (
        appsv1 "k8s.io/api/apps/v1"
        corev1 "k8s.io/api/core/v1"
        "k8s.io/apimachinery/pkg/api/errors"
        metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
        "k8s.io/apimachinery/pkg/types"
        "reflect"

        "context"

        "github.com/go-logr/logr"
        "k8s.io/apimachinery/pkg/runtime"
        ctrl "sigs.k8s.io/controller-runtime"
        "sigs.k8s.io/controller-runtime/pkg/client"
        ctrllog "sigs.k8s.io/controller-runtime/pkg/log"

        cachev1 "github.com/example-inc/memcached-operator/api/v1"
)

// MemcachedReconciler reconciles a Memcached object
type MemcachedReconciler struct {
        client.Client
        Log    logr.Logger
        Scheme *runtime.Scheme
}

// +kubebuilder:rbac:groups=cache.example.com,resources=memcacheds,verbs=get;list;watch;create;update;patch;delete
// +kubebuilder:rbac:groups=cache.example.com,resources=memcacheds/status,verbs=get;update;patch
// +kubebuilder:rbac:groups=cache.example.com,resources=memcacheds/finalizers,verbs=update
// +kubebuilder:rbac:groups=apps,resources=deployments,verbs=get;list;watch;create;update;patch;delete
// +kubebuilder:rbac:groups=core,resources=pods,verbs=get;list;

// Reconcile is part of the main kubernetes reconciliation loop which aims to
// move the current state of the cluster closer to the desired state.
// TODO(user): Modify the Reconcile function to compare the state specified by
// the Memcached object against the actual cluster state, and then
// perform operations to make the cluster state reflect the state specified by
// the user.
//
// For more details, check Reconcile and its Result here:
// - https://pkg.go.dev/sigs.k8s.io/controller-runtime@v0.7.0/pkg/reconcile
func (r *MemcachedReconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
        //log := r.Log.WithValues("memcached", req.NamespacedName)
        log := ctrllog.FromContext(ctx)
        // Fetch the Memcached instance
        memcached := &cachev1.Memcached{}
        err := r.Get(ctx, req.NamespacedName, memcached)
        if err != nil {
                if errors.IsNotFound(err) {
                        // Request object not found, could have been deleted after reconcile request.
                        // Owned objects are automatically garbage collected. For additional cleanup logic use finalizers.
                        // Return and don't requeue
                        log.Info("Memcached resource not found. Ignoring since object must be deleted")
                        return ctrl.Result{}, nil
                }
                // Error reading the object - requeue the request.
                log.Error(err, "Failed to get Memcached")
                return ctrl.Result{}, err
        }

        // Check if the deployment already exists, if not create a new one
        found := &appsv1.Deployment{}
        err = r.Get(ctx, types.NamespacedName{Name: memcached.Name, Namespace: memcached.Namespace}, found)
        if err != nil && errors.IsNotFound(err) {
                // Define a new deployment
                dep := r.deploymentForMemcached(memcached)
                log.Info("Creating a new Deployment", "Deployment.Namespace", dep.Namespace, "Deployment.Name", dep.Name)
                err = r.Create(ctx, dep)
                if err != nil {
                        log.Error(err, "Failed to create new Deployment", "Deployment.Namespace", dep.Namespace, "Deployment.Name", dep.Name)
                        return ctrl.Result{}, err
                }
                // Deployment created successfully - return and requeue
                return ctrl.Result{Requeue: true}, nil
        } else if err != nil {
                log.Error(err, "Failed to get Deployment")
                return ctrl.Result{}, err
        }

        // Ensure the deployment size is the same as the spec
        size := memcached.Spec.Size
        if *found.Spec.Replicas != size {
                found.Spec.Replicas = &size
                err = r.Update(ctx, found)
                if err != nil {
                        log.Error(err, "Failed to update Deployment", "Deployment.Namespace", found.Namespace, "Deployment.Name", found.Name)
                        return ctrl.Result{}, err
                }
                // Spec updated - return and requeue
                return ctrl.Result{Requeue: true}, nil
        }

        // Update the Memcached status with the pod names
        // List the pods for this memcached's deployment
        podList := &corev1.PodList{}
        listOpts := []client.ListOption{
                client.InNamespace(memcached.Namespace),
                client.MatchingLabels(labelsForMemcached(memcached.Name)),
        }
        if err = r.List(ctx, podList, listOpts...); err != nil {
                log.Error(err, "Failed to list pods", "Memcached.Namespace", memcached.Namespace, "Memcached.Name", memcached.Name)
                return ctrl.Result{}, err
        }
        podNames := getPodNames(podList.Items)

        // Update status.Nodes if needed
        if !reflect.DeepEqual(podNames, memcached.Status.Nodes) {
                memcached.Status.Nodes = podNames
                err := r.Status().Update(ctx, memcached)
                if err != nil {
                        log.Error(err, "Failed to update Memcached status")
                        return ctrl.Result{}, err
                }
        }

        return ctrl.Result{}, nil
}

// deploymentForMemcached returns a memcached Deployment object
func (r *MemcachedReconciler) deploymentForMemcached(m *cachev1.Memcached) *appsv1.Deployment {
        ls := labelsForMemcached(m.Name)
        replicas := m.Spec.Size

        dep := &appsv1.Deployment{
                ObjectMeta: metav1.ObjectMeta{
                        Name:      m.Name,
                        Namespace: m.Namespace,
                },
                Spec: appsv1.DeploymentSpec{
                        Replicas: &replicas,
                        Selector: &metav1.LabelSelector{
                                MatchLabels: ls,
                        },
                        Template: corev1.PodTemplateSpec{
                                ObjectMeta: metav1.ObjectMeta{
                                        Labels: ls,
                                },
                                Spec: corev1.PodSpec{
                                        Containers: []corev1.Container{{
                                                Image:   "memcached:1.4.36-alpine",
                                                Name:    "memcached",
                                                Command: []string{"memcached", "-m=64", "-o", "modern", "-v"},
                                                Ports: []corev1.ContainerPort{{
                                                        ContainerPort: 11211,
                                                        Name:          "memcached",
                                                }},
                                        }},
                                },
                        },
                },
        }
        // Set Memcached instance as the owner and controller
        ctrl.SetControllerReference(m, dep, r.Scheme)
        return dep
}

// labelsForMemcached returns the labels for selecting the resources
// belonging to the given memcached CR name.
func labelsForMemcached(name string) map[string]string {
        return map[string]string{"app": "memcached", "memcached_cr": name}
}

// getPodNames returns the pod names of the array of pods passed in
func getPodNames(pods []corev1.Pod) []string {
        var podNames []string
        for _, pod := range pods {
                podNames = append(podNames, pod.Name)
        }
        return podNames
}

// SetupWithManager sets up the controller with the Manager.
func (r *MemcachedReconciler) SetupWithManager(mgr ctrl.Manager) error {
        return ctrl.NewControllerManagedBy(mgr).
                For(&cachev1.Memcached{}).
                Owns(&appsv1.Deployment{}).
                Complete(r)
}


----
====
+
The example controller runs the following reconciliation logic for each `Memcached` custom resource (CR):
+
--
* Create a Memcached deployment if it does not exist.
* Ensure that the deployment size is the same as specified by the `Memcached` CR spec.
* Update the `Memcached` CR status with the names of the `memcached` pods.
--