images

README.md

+# pgouv-operator
+
+This is an operator made for training purpose. It leverages Kubernetes API
+by installing CRD(`api/v1alpha1/pkg/pgouv_types.go`)
+to the Kubernetes Cluster and reconciling in order to match the desired
+state described in `Spec` to the observed state (`Status`).
+
+## Objective
+The purpose of this controller is to create the a number of pods that will
+run a command.Both the pods and the command will be provided in CRD.
+
+
+## Prerequesties 
+* Running Kubernetes 1.15+ cluster (e.g [kind](https://kind.sigs.k8s.io/ ))
+* kubebuilder 2.20 ([install from site](https://kind.sigs.k8s.io/))
+* go 1.13+
+
+
+## Set-up
+1. Clone the directory
+```bash
+git clone  https://gitlab.ubitech.eu/iplakas/first-controller
+cd first-controller
+```
+2. Kubernetes does not know/have a definition about the created type (`pgouv_types.go`)
+```bash
+kubectl get crds
+```
+![Image of crds](https://gitlab.ubitech.eu/iplakas/first-controller/-/blob/master/images/empty-crds.png)
+
+3.  Install the CRD to the cluster
+```bash
+make manifests
+make install 
+```
+The created resource is retrieved `kubectl get crd`
+![Image of new  crds](https://gitlab.ubitech.eu/iplakas/first-controller/-/blob/master/images/crds.png)
+
+4.  The generated CRD is fully described in yaml format in `config/crd/bases/ubi.ubitech.eu_pgouvs.yaml`  which is generated by the corresponding go type
+
+```go
+// PgouvSpec defines the desired state of Pgouv
+type PgouvSpec struct {
+ // INSERT ADDITIONAL SPEC FIELDS - desired state of cluster
+ // Important: Run "make" to regenerate code after modifying this file
+ // Foo is an example field of Pgouv. Edit Pgouv_types.go to remove/update
+ Command string `json:"command"`
+ Replicas int32 `json:"replicas"`
+}
+// PgouvStatus defines the observed state of Pgouv
+type PgouvStatus struct {
+ // INSERT ADDITIONAL STATUS FIELD - define observed state of cluster
+ // Important: Run "make" to regenerate code after modifying this file
+ AliveRelplicas int32 `json:"alivereplicas,omitempty"`
+}
+```
+
+5. Now that the Kubernetes Cluster knows about the Custom Resource 
+its time to initiate one, we do  that be updating the `config/samples/ubi_v1alpha1_pgouv` file (the name of file follows the GVK convention)
+
+```go
+apiVersion: ubi.ubitech.eu/v1alpha1
+kind: Pgouv
+metadata:
+ name: pgouv-sample
+spec:
+ # Add fields here
+ command: "echo  ORIGINAL21"
+ replicas: 3
+```
+In order to apply the instance of the resource `kubectl applay -f config/samples/ubi_v1alpha1_pgouv`
+
+![Created resource ](https://gitlab.ubitech.eu/iplakas/first-controller/-/blob/master/images/created.png)
+
+
+6. Now that the cluster has  a  Custom Resource  the determined logic 
+served with it is written in `controllers\pgouv_controller.go` 
+
+```go 
+// PgouvReconciler reconciles a Pgouv object
+type PgouvReconciler struct {
+ client.Client
+ Log    logr.Logger
+ Scheme *runtime.Scheme
+}
+// +kubebuilder:rbac:groups=apps,resources=deployments,verbs=get;list;watch;create;update;patch;delete
+// +kubebuilder:rbac:groups=apps,resources=deployments/status,verbs=get;update;patch
+// +kubebuilder:rbac:groups=ubi.ubitech.eu,resources=pgouvs,verbs=get;list;watch;create;update;patch;delete
+// +kubebuilder:rbac:groups=ubi.ubitech.eu,resources=pgouvs/status,verbs=get;update;patch
+func (r *PgouvReconciler) Reconcile(req ctrl.Request) (ctrl.Result, error) {
+ context := context.Background()
+ //fitst step create the logger
+ logger := r.Log.WithValues("pgouv", req.NamespacedName)
+ logger.Info("just starded")
+```
+The reconcile logic will be called once new Events regrading the handled resource
+(and the sub-Resources that owns) are detected . That's why `role-based-access-control` needs to be provided to the Controller(eg. `kubebuilder:rbac:`).
+
+7. The difference that Reconcile Function uses in order to get to the desired state 
+is described in the following snippet 
+
+```go
+//just to get the items right
+ podlist := &corev1.PodList{}
+ err = r.List(context, podlist, client.InNamespace(req.Namespace), client.MatchingLabels{"app": instance.Name})
+ if err != nil {
+	 if errors.IsNotFound(err) {
+	 return reconcile.Result{}, nil
+	 }
+ return reconcile.Result{}, err
+ }
+ instance.Status.AliveRelplicas = int32(len(podlist.Items))
+ diff := instance.Spec.Replicas - instance.Status.AliveRelplicas
+```
+Firstly the Status of the CR is determined by retrieving the number of pods (owned by the Resource). Then the difference between `Spec` and `Status` will 
+determine if more Pods running the specified `Command` are needed or
+Pods need to get deleted.
+
+8. The example logic in controller : 
+
+```go
+//need to create
+ if diff > 0 {
+ logger.Info("Need to reconcile invrementaly")
+ //Define new pod object
+ pod := spawn.NewPodForCR(instance)
+ //Set owner for the pod before initiate it
+ if err = controllerutil.SetControllerReference(instance, pod, r.Scheme); err != nil {
+ return reconcile.Result{}, err
+ }
+ err = r.Create(context, pod)
+ if err != nil {
+ if errors.IsNotFound(err) {
+ return reconcile.Result{}, nil
+ }
+ return reconcile.Result{}, err
+ }
+ instance.Status.AliveRelplicas++
+ err = r.Status().Update(context, instance)
+ if err != nil {
+ return ctrl.Result{}, err
+ }
+ logger.Info("Pod created")
+ return reconcile.Result{}, err
+```
+Or when we need to delete Pods 
+
+```go
+else if diff < 0 {
+ logger.Info("need to delete a pod")
+ podlist := &corev1.PodList{}
+ //lbs := map[string]string{
+ //	"app": instance.Name,
+ //	}
+ //labelSelector := labels.SelectorFromSet(lbs)
+ //	lsopt := &client.ListOption{LabelSelector: labelSelector, Namespace: instance.name}
+ err := r.List(context, podlist, client.InNamespace(req.Namespace), client.MatchingLabels{"app": instance.Name})
+ if err != nil {
+ if errors.IsNotFound(err) {
+ return reconcile.Result{}, nil
+ }
+ return reconcile.Result{}, err
+ }
+ logger.Info("Deleted Pod")
+ instance.Status.AliveRelplicas--
+ logger.Info("Update deteted status")
+ err = r.Status().Update(context, instance)
+ if err != nil {
+ return ctrl.Result{}, err
+ }
+ err = r.Delete(context, &podlist.Items[0])
+ if err != nil {
+ return reconcile.Result{}, err
+ }
+ return reconcile.Result{}, nil
+ }
+```
+
+9.  The Reconcile function  needs to have a Manger (possibly managing other controllers/reconcilers)
+which is resposible for the shared depedancies (e.g Client , Cache)
+The manager handles a reconcile function that is triggered by events(Add,Delete
+,Update) on the CR and the Pod resources created from it.
+
+```go
+func (r *PgouvReconciler) SetupWithManager(mgr ctrl.Manager) error {
+return ctrl.NewControllerManagedBy(mgr).
+	For(&ubiv1alpha1.Pgouv{}).
+	Owns(&corev1.Pod{}).
+	Complete(r)
+}
+``` 
+
+
+
+10. Run the Controller :
+```bash
+make run
+```
+`kubectl logs ` will retrieve the output of the `Command` for the specified Pod
+
+
+![Created resource ](https://gitlab.ubitech.eu/iplakas/first-controller/-/blob/master/images/output.png)
+
+
+11. The CR can be updated by updating the `Replicas` field on the `config/samples/ubi_v1alpha1_pgouv` and applying it to the cluster via
+`kubectl apply -f `
+
+[Created resource2 ](https://gitlab.ubitech.eu/iplakas/first-controller/-/blob/master/images/output2.png)
+
+
+
+                                                                                 
+
+

config/samples/ubi_v1alpha1_pgouv.yaml

@@ -5,4 +5,4 @@ metadata:
 spec:
   # Add fields here
   command: "echo ORIGINAL21"
-  replicas: 3
+  replicas: 5

controllers/pgouv_controller.go

@@ -104,7 +104,7 @@ func (r *PgouvReconciler) Reconcile(req ctrl.Request) (ctrl.Result, error) {
 	} else if diff < 0 {
 		logger.Info("need to delete a pod")
 		podlist := &corev1.PodList{}
-	  err := r.List(context, podlist, client.InNamespace(req.Namespace), client.MatchingLabels{"app": instance.Name})
+		err := r.List(context, podlist, client.InNamespace(req.Namespace), client.MatchingLabels{"app": instance.Name})
 		if err != nil {
 			if errors.IsNotFound(err) {
 				return reconcile.Result{}, nil