Allow intermediate replicas to ease operation

Currently the mariadb operator has webhooks to enforce the galera
replica count to be either 1 or 3, which are the two supported
deployments on the OpenstackControlPlane.

However there is a need for more flexibility for day two operations,
where it can be useful to allow scaling down replicas temporarily
to e.g. 2 (for replacement procedure) or even 0 (to temporarily disable
database management).

Replace the kubebuilder annotations with minimum and maximum, and
let the galera webhook warn about setting replicas to 2 (as it is not
advisable to keep that setting for quorum concerns).

api/bases/mariadb.openstack.org_galeras.yaml

@@ -69,11 +69,9 @@ spec:
               replicas:
                 default: 1
                 description: Size of the galera cluster deployment
-                enum:
-                - 1
-                - 3
                 format: int32
-                minimum: 1
+                maximum: 3
+                minimum: 0
                 type: integer
               secret:
                 description: Name of the secret to look for password keys

api/v1beta1/galera_types.go

@@ -57,9 +57,9 @@ type GaleraSpecCore struct {
 	// Storage size allocated for the mariadb databases
 	// +kubebuilder:validation:Required
 	StorageRequest string `json:"storageRequest"`
-	// +kubebuilder:validation:Minimum=1
+	// +kubebuilder:validation:Minimum=0
+	// +kubebuilder:validation:Maximum=3
 	// +kubebuilder:default=1
-	// +kubebuilder:validation:Enum=1;3
 	// Size of the galera cluster deployment
 	Replicas *int32 `json:"replicas"`
 	// +kubebuilder:validation:Optional

api/v1beta1/galera_webhook.go

@@ -120,20 +120,28 @@ func (spec *GaleraSpecCore) ValidateCreate(basePath *field.Path) (admission.Warn
 	warn, _ := common_webhook.ValidateStorageRequest(basePath, spec.StorageRequest, storageRequestProdMin, false)
 	allWarn = append(allWarn, warn...)
 
+	warn = spec.ValidateGaleraReplicas(basePath)
+	allWarn = append(allWarn, warn...)
+
 	return allWarn, allErrs
 }
 
 // ValidateUpdate implements webhook.Validator so a webhook will be registered for the type
 func (r *Galera) ValidateUpdate(old runtime.Object) (admission.Warnings, error) {
+	allWarn := []string{}
 	galeralog.Info("validate update", "name", r.Name)
 
 	oldGalera, ok := old.(*Galera)
 	if !ok || oldGalera == nil {
 		return nil, apierrors.NewInternalError(fmt.Errorf("unable to convert existing object"))
 	}
 
+	basePath := field.NewPath("spec")
+	warn := r.Spec.ValidateGaleraReplicas(basePath)
+	allWarn = append(allWarn, warn...)
+
 	// TODO(user): fill in your validation logic upon object update.
-	return nil, nil
+	return allWarn, nil
 }
 
 // ValidateDelete implements webhook.Validator so a webhook will be registered for the type
@@ -149,3 +157,15 @@ func SetupGaleraDefaults(defaults GaleraDefaults) {
 	galeraDefaults = defaults
 	galeralog.Info("Galera defaults initialized", "defaults", defaults)
 }
+
+// SetupGaleraDefaults - Check whether replica count is valid for quorum
+func (spec *GaleraSpecCore) ValidateGaleraReplicas(basePath *field.Path) admission.Warnings {
+	replicas := int(*spec.Replicas)
+	if replicas > 0 && (replicas%2 == 0) {
+		res := fmt.Sprintf("%s: %d is not appropriate for quorum! Use an odd value!",
+			basePath.Child("replicas").String(), replicas)
+		return []string{res}
+	} else {
+		return nil
+	}
+}

config/crd/bases/mariadb.openstack.org_galeras.yaml

@@ -69,11 +69,9 @@ spec:
               replicas:
                 default: 1
                 description: Size of the galera cluster deployment
-                enum:
-                - 1
-                - 3
                 format: int32
-                minimum: 1
+                maximum: 3
+                minimum: 0
                 type: integer
               secret:
                 description: Name of the secret to look for password keys

controllers/galera_controller.go

@@ -819,7 +819,7 @@ func (r *GaleraReconciler) Reconcile(ctx context.Context, req ctrl.Request) (res
 		}
 
 		// Check if we have enough info to bootstrap the cluster now
-		if !found {
+		if !found && int(*instance.Spec.Replicas) > 0 {
 			node, found = findBestCandidate(instance)
 		}
 		if found {