From afeefafb15c4bc40f290ee6fc66e8a71df5ed9eb Mon Sep 17 00:00:00 2001
From: Qi Ni <pomelonicky@gmail.com>
Date: Wed, 13 Oct 2021 20:40:17 +0800
Subject: [PATCH] fix: skip instance not found when decoupling vmss from lb

(cherry picked from commit 0b7ba30b1b734172f5005185d09fb641e105405b)
---
 pkg/provider/azure_vmss.go      |  5 +++++
 pkg/provider/azure_vmss_test.go | 23 +++++++++++++++++++++--
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/pkg/provider/azure_vmss.go b/pkg/provider/azure_vmss.go
index f275873e5a..49432d0b4f 100644
--- a/pkg/provider/azure_vmss.go
+++ b/pkg/provider/azure_vmss.go
@@ -1517,6 +1517,11 @@ func (ss *ScaleSet) EnsureBackendPoolDeleted(service *v1.Service, backendPoolID,
 				continue
 			}
 
+			if errors.Is(err, cloudprovider.InstanceNotFound) {
+				klog.Infof("EnsureBackendPoolDeleted(%s): skipping ip config %s because the corresponding vmss vm is not found", getServiceName(service), ipConfigurationID)
+				continue
+			}
+
 			klog.Errorf("Failed to GetNodeNameByIPConfigurationID(%s): %v", ipConfigurationID, err)
 			allErrs = append(allErrs, err)
 			continue
diff --git a/pkg/provider/azure_vmss_test.go b/pkg/provider/azure_vmss_test.go
index d7343587c6..f7206c57b4 100644
--- a/pkg/provider/azure_vmss_test.go
+++ b/pkg/provider/azure_vmss_test.go
@@ -2424,6 +2424,26 @@ func TestEnsureBackendPoolDeleted(t *testing.T) {
 			expectedErr:            true,
 			vmClientErr:            &retry.Error{RawError: fmt.Errorf("error")},
 		},
+		{
+			description:   "EnsureBackendPoolDeleted should skip the node that doesn't exist",
+			backendpoolID: testLBBackendpoolID0,
+			backendAddressPools: &[]network.BackendAddressPool{
+				{
+					ID: to.StringPtr(testLBBackendpoolID0),
+					BackendAddressPoolPropertiesFormat: &network.BackendAddressPoolPropertiesFormat{
+						BackendIPConfigurations: &[]network.InterfaceIPConfiguration{
+							{
+								Name: to.StringPtr("ip-1"),
+								ID:   to.StringPtr("/subscriptions/sub/resourceGroups/rg/providers/Microsoft.Compute/virtualMachineScaleSets/vmss/virtualMachines/6/networkInterfaces/nic"),
+							},
+						},
+					},
+				},
+				{
+					ID: to.StringPtr(testLBBackendpoolID1),
+				},
+			},
+		},
 	}
 
 	for _, test := range testCases {
@@ -2477,7 +2497,6 @@ func TestEnsureBackendPoolDeletedConcurrently(t *testing.T) {
 			},
 		},
 		{
-			// this would fail
 			ID: to.StringPtr(testLBBackendpoolID2),
 			BackendAddressPoolPropertiesFormat: &network.BackendAddressPoolPropertiesFormat{
 				BackendIPConfigurations: &[]network.InterfaceIPConfiguration{
@@ -2516,7 +2535,7 @@ func TestEnsureBackendPoolDeletedConcurrently(t *testing.T) {
 	mockVMSSVMClient.EXPECT().UpdateVMs(gomock.Any(), ss.ResourceGroup, gomock.Any(), gomock.Any(), gomock.Any()).Return(nil).Times(2)
 
 	backendpoolAddressIDs := []string{testLBBackendpoolID0, testLBBackendpoolID1, testLBBackendpoolID2}
-	testVMSSNames := []string{"vmss-0", "vmss-1", "vmss-0"}
+	testVMSSNames := []string{"vmss-0", "vmss-1", "vmss-2"}
 	testFunc := make([]func() error, 0)
 	for i, id := range backendpoolAddressIDs {
 		i := i