fix: h-scale opsRequest validation considers replicas and shards limit

apis/operations/v1alpha1/opsrequest_validation.go

@@ -438,6 +438,9 @@ func (r *OpsRequest) validateHorizontalScalingSpec(hScale HorizontalScaling, com
 		if replicaChanger.ReplicaChanges != nil && allReplicaChanges > *replicaChanger.ReplicaChanges {
 			return fmt.Errorf(`%s "replicaChanges" can't be less than the sum of "replicaChanges" for specified instance templates`, msgPrefix)
 		}
+		if isScaleIn && len(offlineOrOnlineInsNames) == int(compSpec.Replicas) {
+			return fmt.Errorf(`scaling down all the replicas of component "%s" is not allowed`, hScale.ComponentName)
+		}
 		return nil
 	}
 	if scaleIn != nil {

controllers/operations/opsrequest_controller_test.go

@@ -475,6 +475,30 @@ var _ = Describe("OpsRequest Controller", func() {
 			})).Should(Succeed())
 		})
 
+		It("HorizontalScaling when offline the only instance in MySQL", func() {
+			createMysqlCluster(2)
+			By("mock cluster status")
+			Expect(testapps.ChangeObj(&testCtx, clusterObj, func(clusterObj *appsv1.Cluster) {
+				mockSetClusterStatusPhaseToRunning(clusterKey)
+			})).Should(Succeed())
+			ops := testops.NewOpsRequestObj("test-ops", testCtx.DefaultNamespace,
+				clusterObj.Name, opsv1alpha1.HorizontalScalingType)
+			ops.Spec.HorizontalScalingList = []opsv1alpha1.HorizontalScaling{
+				{
+					ComponentOps: opsv1alpha1.ComponentOps{ComponentName: mysqlCompName},
+					ScaleIn: &opsv1alpha1.ScaleIn{
+						OnlineInstancesToOffline: []string{clusterNamePrefix + mysqlCompName + "-0", clusterNamePrefix + mysqlCompName + "-1"},
+					},
+				},
+			}
+			ops.Labels = nil
+
+			err := ops.Validate(ctx, nil, clusterObj, true)
+
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(ContainSubstring("scaling down all the replicas of component"))
+		})
+
 		It("delete Running opsRequest", func() {
 			By("Create a horizontalScaling ops")
 			createMysqlCluster(3)