test: add the tests when public ip already exists in azure profile

docs/demos/TrafficManagerProfile/session-migrate-to-another-cluster/README.md

@@ -152,7 +152,7 @@ spec:
 ---
 
 ## Step 4: Clean Up Resources Using the `eviction` API
-- Remove the env label from the `aks-member-1` or add [a taint on the member](https://github.com/Azure/fleet/blob/main/docs/howtos/taint-toleration.md) so that the cluster won't be picked by the `clusterResourcePlacement` again.
+- Remove the env label from the `aks-member-1` or add [a taint on the member](https://kubefleet-dev.github.io/website/docs/how-tos/taints-tolerations/) so that the cluster won't be picked by the `clusterResourcePlacement` again.
 - Safely remove application workloads and services from `aks-member-1` once all traffic has shifted and all the client DNS caches are refreshed.
 
 > Note: test file located [here](../testfiles/placement-eviction-member-1.yaml).

docs/demos/TrafficManagerProfile/session-migrate-to-another-region/README.md

@@ -163,7 +163,7 @@ kubectl apply -f nginx-backend-uksouth.yaml
 > So that most of the traffic can be shifted to the new regions before deleting endpoints from eastus2euap region.
 
 ## Step 6: Cleanup & Finalization
-- Remove the env label from the `aks-member-1` & `aks-member-3` or add [a taint on these two members](https://github.com/Azure/fleet/blob/main/docs/howtos/taint-toleration.md) so that the cluster won't be picked by the `clusterResourcePlacement` again.
+- Remove the env label from the `aks-member-1` & `aks-member-3` or add [a taint on these two members](https://kubefleet-dev.github.io/website/docs/how-tos/taints-tolerations/) so that the cluster won't be picked by the `clusterResourcePlacement` again.
 - To ensure the application won't be disrupted, we can create the `ClusterResourcePlacementDisruptionBudget` for the protection.
 
 > Note: test file located [here](../testfiles/placement-disruption-budget.yaml).

docs/toubleshooting/DNSBasedGlobalLoadBalancing.md

@@ -125,7 +125,27 @@ Common reasons and solutions for `TrafficManagerBackend` not being accepted:
    ```
 4. Not enough permissions to read the public IP address of the exported `Service` on the members.
    - Ensure fleet hub networking controller has been configured correctly to access public IP address of services on the members.
-5. [Reach the Azure Traffic Manager limits](https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/azure-subscription-service-limits#azure-traffic-manager-limits).
+5. The public IP address already exists in the Azure Traffic Manager profile.
+   - Please use the existing trafficManagerBackend to manage your endpoints exported by the service. It happens that you've already added
+   endpoints to the profile by creating the trafficManagerBackend using the same service name and profile name.
+   ```yaml
+   # sample status
+    status:
+    conditions:
+    - lastTransitionTime: "2025-05-16T08:43:33Z"
+      message: "2 endpoint(s) failed to be created/updated in the Azure Traffic Manager,
+        for example, PUT https://management.azure.com/subscriptions/c4528d9e-c99a-48bb-b12d-fde2176a43b8/resourceGroups/zhiyinglin-fleet-dev/providers/Microsoft.Network/trafficmanagerprofiles/fleet-5abc2041-c627-4937-ab04-ffd493975adb/AzureEndpoints/fleet-390eca1c-fdb2-49c8-bf28-3e4fc2660b08#hello-world-service#dev-member-2\n--------------------------------------------------------------------------------\nRESPONSE
+        400: 400 Bad Request\nERROR CODE: BadRequest\n--------------------------------------------------------------------------------\n{\n
+        \ \"error\": {\n    \"code\": \"BadRequest\",\n    \"message\": \"Endpoint
+        target must be unique in the profile. The following endpoint target already
+        exists: \\/subscriptions\\/c4528d9e-c99a-48bb-b12d-fde2176a43b8\\/resourceGroups\\/mc_zhiyinglin-fleet-dev_dev-member-2_eastus2\\/providers\\/Microsoft.Network\\/publicIPAddresses\\/kubernetes-ab5eea9ca3a6d44238cf82ef2e45b41a.\"\n
+        \ }\n}\n--------------------------------------------------------------------------------\n; "
+      observedGeneration: 1
+      reason: Invalid
+      status: "False"
+      type: Accepted
+   ```
+6. [Reach the Azure Traffic Manager limits](https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/azure-subscription-service-limits#azure-traffic-manager-limits).
     - 200 endpoints are allowed per profile. If the limit is reached, consider deleting unused endpoints or requesting an increase in the limit.
 
 Please check the `status` field of the `TrafficManagerBackend` or the `trafficmanagerbackend/controller.go` hub-net-controller-manager logs for more information.

test/e2e/traffic_manager_test.go

@@ -418,7 +418,7 @@ var _ = Describe("Test exporting service via Azure traffic manager", Ordered, fu
 
 		AfterEach(func() {
 			By("Deleting trafficManagerBackend")
-			Expect(hubClient.Delete(ctx, &backend)).Should(Succeed(), "Failed to delete the trafficManagerBackend")
+			Expect(client.IgnoreNotFound(hubClient.Delete(ctx, &backend))).Should(Succeed(), "Failed to delete the trafficManagerBackend")
 			validator.IsTrafficManagerBackendDeleted(ctx, hubClient, backendName, lightAzureOperationTimeout)
 
 			By("Validating the Azure traffic manager profile")
@@ -442,6 +442,56 @@ var _ = Describe("Test exporting service via Azure traffic manager", Ordered, fu
 			atmValidator.ValidateProfile(ctx, atmProfileName, atmProfile)
 		})
 
+		It("Creating another trafficManagerBackend to export the same service", func() {
+			By("Creating an invalid trafficManagerBackend")
+			invalidBackend := wm.TrafficManagerBackend()
+			invalidBackend.Name = fmt.Sprintf("%s-%s", backend.Name, "invalid")
+			invalidBackendName := types.NamespacedName{Namespace: invalidBackend.Namespace, Name: invalidBackend.Name}
+			Expect(hubClient.Create(ctx, &invalidBackend)).Should(Succeed(), "Failed to create the trafficManagerBackend")
+
+			By("Validating the invalidBackend trafficManagerBackend status")
+			status := validator.ValidateTrafficManagerBackendIfAcceptedAndIgnoringEndpointName(ctx, hubClient, invalidBackendName, false, nil, lightAzureOperationTimeout)
+			validator.ValidateTrafficManagerBackendStatusAndIgnoringEndpointNameConsistently(ctx, hubClient, invalidBackendName, status)
+
+			By("Validating the Azure traffic manager profile")
+			// No changes should be made to the profile.
+			atmValidator.ValidateProfile(ctx, atmProfileName, atmProfile)
+
+			By("Deleting existing trafficManagerBackend")
+			Expect(hubClient.Delete(ctx, &backend)).Should(Succeed(), "Failed to delete the trafficManagerBackend")
+			validator.IsTrafficManagerBackendDeleted(ctx, hubClient, backendName, lightAzureOperationTimeout)
+
+			By("Validating the invalid trafficManagerBackend status and should be accepted now")
+			wantEndpoints := []fleetnetv1beta1.TrafficManagerEndpointStatus{
+				{
+					Weight: ptr.To(int64(50)),
+					Target: ptr.To(fmt.Sprintf(azureDNSFormat, memberDNSLabels[0], clusterLocation)),
+					From: &fleetnetv1beta1.FromCluster{
+						ClusterStatus: fleetnetv1beta1.ClusterStatus{Cluster: memberClusters[0].Name()},
+						Weight:        ptr.To(int64(1)),
+					},
+				},
+				{
+					Weight: ptr.To(int64(50)),
+					Target: ptr.To(fmt.Sprintf(azureDNSFormat, memberDNSLabels[1], clusterLocation)),
+					From: &fleetnetv1beta1.FromCluster{
+						ClusterStatus: fleetnetv1beta1.ClusterStatus{Cluster: memberClusters[1].Name()},
+						Weight:        ptr.To(int64(1)),
+					},
+				},
+			}
+			status = validator.ValidateTrafficManagerBackendIfAcceptedAndIgnoringEndpointName(ctx, hubClient, invalidBackendName, true, wantEndpoints, heavyAzureOperationTimeout)
+			validator.ValidateTrafficManagerBackendStatusAndIgnoringEndpointNameConsistently(ctx, hubClient, invalidBackendName, status)
+
+			By("Validating the Azure traffic manager profile")
+			atmProfile = buildDesiredATMProfile(profile, status.Endpoints)
+			atmProfile = *atmValidator.ValidateProfile(ctx, atmProfileName, atmProfile)
+
+			By("Deleting invalid trafficManagerBackend")
+			Expect(hubClient.Delete(ctx, &invalidBackend)).Should(Succeed(), "Failed to delete the trafficManagerBackend")
+			validator.IsTrafficManagerBackendDeleted(ctx, hubClient, invalidBackendName, lightAzureOperationTimeout)
+		})
+
 		It("Creating extra Azure traffic manager endpoint directly and then updating trafficManagerBackend", func() {
 			By("Creating a public IP address")
 			publicIPAddressName := fmt.Sprintf("e2e-test-public-ip-%s", uniquename.RandomLowerCaseAlphabeticString(5))