Add cluster size validation rule

api/v1alpha1/nats_types.go

@@ -125,6 +125,7 @@ type Cluster struct {
 	// +kubebuilder:default:=3
 	// +kubebuilder:validation:Minimum:=1
 	// +kubebuilder:validation:XValidation:rule="(self%2) != 0", message="size only accepts odd numbers"
+	// +kubebuilder:validation:XValidation:rule="!(oldSelf > 1 && self == 1)", message="size cannot be reduced to 1 once it was >1"
 	Size int `json:"size,omitempty"`
 }
 

config/crd/bases/operator.kyma-project.io_nats.yaml

@@ -83,6 +83,8 @@ spec:
                     x-kubernetes-validations:
                     - message: size only accepts odd numbers
                       rule: (self%2) != 0
+                    - message: size cannot be reduced to 1 once it was >1
+                      rule: '!(oldSelf > 1 && self == 1)'
                 type: object
               jetStream:
                 default:

internal/controller/nats/integrationtests/validation/integration_test.go

@@ -267,6 +267,36 @@ func Test_Validate_UpdateNATS(t *testing.T) {
 			},
 			wantErrMsg: "fileStorage is immutable once it was set",
 		},
+		{
+			name: `validation of cluster fails, if cluster.size>1 gets set to 1'`,
+			givenNATS: testutils.NewNATSCR(
+				testutils.WithNATSCluster(defaultCluster()),
+			),
+			wantMatches: gomega.And(
+				natsmatchers.HaveSpecCluster(defaultCluster()),
+			),
+			givenUpdates: []testutils.NATSOption{
+				testutils.WithNATSCluster(v1alpha1.Cluster{
+					Size: 1,
+				}),
+			},
+			wantErrMsg: "size cannot be reduced to 1 once it was >1",
+		},
+		{
+			name: `validation of cluster passes, if cluster.size>1 gets set to >1'`,
+			givenNATS: testutils.NewNATSCR(
+				testutils.WithNATSCluster(defaultCluster()),
+			),
+			wantMatches: gomega.And(
+				natsmatchers.HaveSpecCluster(defaultCluster()),
+			),
+			givenUpdates: []testutils.NATSOption{
+				testutils.WithNATSCluster(v1alpha1.Cluster{
+					Size: 5,
+				}),
+			},
+			wantErrMsg: noError,
+		},
 	}
 
 	for _, tc := range testCases {

testutils/options.go

@@ -210,6 +210,13 @@ func WithNATSFileStorage(fileStorage v1alpha1.FileStorage) NATSOption {
 	}
 }
 
+func WithNATSCluster(cluster v1alpha1.Cluster) NATSOption {
+	return func(nats *v1alpha1.NATS) error {
+		nats.Spec.Cluster = cluster
+		return nil
+	}
+}
+
 func WithNATSLabels(labels map[string]string) NATSOption {
 	return func(nats *v1alpha1.NATS) error {
 		nats.Spec.Labels = labels