Repository: kubernetes-sigs/cloud-provider-azure (go)

Issue:
UDP services may trigger unnecessary LoadBalancer updates
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#### What happened:

While nothing changed to all LoadBalancer service specs, scaling node number or restart controller manager would trigger LoadBalancer update APIs. This is because `EnableTCPReset` value is different between expected LB rule and existing LB rule when the protocol is not TCP, and hence `equalLoadBalancingRulePropertiesFormat()` would treat the LB rule as updated.

And here are the related logs:

```
I0129 07:27:01.471484       1 azure_loadbalancer.go:1516] reconcileLoadBalancer for service(default/test): lb(test-rg/kubernetes) wantLb(true) resolved load balancer name
I0129 07:27:01.530862       1 azure_loadbalancer.go:2106] getExpectedLBRules lb name (kubernetes) rule name (a30cf55982b684c1993a23dd1e177c98-UDP-24899)
I0129 07:27:01.530954       1 azure_loadbalancer.go:1696] reconcileLoadBalancer for service (default/test)(true): lb rule(a30cf55982b684c1993a23dd1e177c98-UDP-24899) - dropping
```

#### What you expected to happen:

* `EnableTCPReset` should only be set in LB rule when the protocol is TCP.
* `equalLoadBalancingRulePropertiesFormat` should omit `EnableTCPReset` when protocol is not TCP.

#### How to reproduce it (as minimally and precisely as possible):

Create a UDP LoadBalancer service in the cluster and then restart controller manager. After a while, there would be new write operations in LoadBalancer activities （this could be observed on the Azure portal）.

#### Anything else we need to know?:

#### Environment:

- Kubernetes version (use `kubectl version`):
- Cloud provider or hardware configuration:
- OS (e.g: `cat /etc/os-release`):
- Kernel (e.g. `uname -a`):
- Install tools:
- Network plugin and version (if this is a network-related bug):
- Others:


Pull request:
Cherry-pick: Fix incorrect EnableTCPReset for non-TCP protocols
Signed-off-by: Zhecheng Li <zhechengli@microsoft.com>

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#### What type of PR is this?

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#### What this PR does / why we need it:

#### Which issue(s) this PR fixes:
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Fixes #1087

#### Special notes for your reviewer:

#### Does this PR introduce a user-facing change?
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```release-note
This code change fixes the bug that UDP services would trigger unnecessary LoadBalancer updates. The root cause is that a field not working for non-TCP protocols is considered.
ref: #1090
```

#### Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

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```docs

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Patch:
diff --git a/pkg/provider/azure_loadbalancer.go b/pkg/provider/azure_loadbalancer.go
index d6d5b5bbd..48213b963 100644
--- a/pkg/provider/azure_loadbalancer.go
+++ b/pkg/provider/azure_loadbalancer.go
@@ -2065,7 +2065,7 @@ func (az *Cloud) getExpectedLBRules(
 		ports = []v1.ServicePort{}
 	}
 
-	var enableTCPReset *bool
+	var enableTCPReset, nilTCPReset *bool
 	if az.useStandardLoadBalancer() {
 		enableTCPReset = to.BoolPtr(true)
 	}
@@ -2143,6 +2143,10 @@ func (az *Cloud) getExpectedLBRules(
 			loadDistribution = network.LoadDistributionSourceIP
 		}
 
+		tcpReset := enableTCPReset
+		if port.Protocol != v1.ProtocolTCP {
+			tcpReset = nilTCPReset
+		}
 		expectedRule := network.LoadBalancingRule{
 			Name: &lbRuleName,
 			LoadBalancingRulePropertiesFormat: &network.LoadBalancingRulePropertiesFormat{
@@ -2157,7 +2161,7 @@ func (az *Cloud) getExpectedLBRules(
 				FrontendPort:        to.Int32Ptr(port.Port),
 				BackendPort:         to.Int32Ptr(port.Port),
 				DisableOutboundSnat: to.BoolPtr(az.disableLoadBalancerOutboundSNAT()),
-				EnableTCPReset:      enableTCPReset,
+				EnableTCPReset:      tcpReset,
 				EnableFloatingIP:    to.BoolPtr(true),
 			},
 		}
@@ -2936,14 +2940,21 @@ func equalLoadBalancingRulePropertiesFormat(s *network.LoadBalancingRuleProperti
 		return false
 	}
 
-	properties := reflect.DeepEqual(s.Protocol, t.Protocol) &&
-		reflect.DeepEqual(s.FrontendIPConfiguration, t.FrontendIPConfiguration) &&
+	properties := reflect.DeepEqual(s.Protocol, t.Protocol)
+	if !properties {
+		return false
+	}
+
+	if reflect.DeepEqual(s.Protocol, network.TransportProtocolTCP) {
+		properties = properties && reflect.DeepEqual(to.Bool(s.EnableTCPReset), to.Bool(t.EnableTCPReset))
+	}
+
+	properties = properties && reflect.DeepEqual(s.FrontendIPConfiguration, t.FrontendIPConfiguration) &&
 		reflect.DeepEqual(s.BackendAddressPool, t.BackendAddressPool) &&
 		reflect.DeepEqual(s.LoadDistribution, t.LoadDistribution) &&
 		reflect.DeepEqual(s.FrontendPort, t.FrontendPort) &&
 		reflect.DeepEqual(s.BackendPort, t.BackendPort) &&
 		reflect.DeepEqual(s.EnableFloatingIP, t.EnableFloatingIP) &&
-		reflect.DeepEqual(to.Bool(s.EnableTCPReset), to.Bool(t.EnableTCPReset)) &&
 		reflect.DeepEqual(to.Bool(s.DisableOutboundSnat), to.Bool(t.DisableOutboundSnat))
 
 	if wantLB && s.IdleTimeoutInMinutes != nil && t.IdleTimeoutInMinutes != nil {


Test patch:
diff --git a/pkg/provider/azure_loadbalancer_test.go b/pkg/provider/azure_loadbalancer_test.go
index d691d606e..fdd50e86e 100644
--- a/pkg/provider/azure_loadbalancer_test.go
+++ b/pkg/provider/azure_loadbalancer_test.go
@@ -1781,7 +1781,7 @@ func TestReconcileLoadBalancerRule(t *testing.T) {
 			}, false, 80),
 			loadBalancerSku: "standard",
 			wantLb:          true,
-			expectedRules:   getHATestRules(true, false, v1.ProtocolSCTP),
+			expectedRules:   getHATestRules(false, false, v1.ProtocolSCTP),
 		},
 		{
 			desc: "getExpectedLBRules shall return corresponding probe and lbRule (slb with HA enabled multi-ports services)",
@@ -4647,3 +4647,48 @@ func TestReconcileSharedLoadBalancer(t *testing.T) {
 		})
 	}
 }
+
+func TestEqualLoadBalancingRulePropertiesFormat(t *testing.T) {
+	var enableTCPReset, disableTCPReset *bool = to.BoolPtr(true), to.BoolPtr(false)
+	var frontPort *int32 = to.Int32Ptr(80)
+
+	testcases := []struct {
+		s        *network.LoadBalancingRulePropertiesFormat
+		t        *network.LoadBalancingRulePropertiesFormat
+		wantLb   bool
+		expected bool
+	}{
+		{
+			s: &network.LoadBalancingRulePropertiesFormat{
+				Protocol:       network.TransportProtocolTCP,
+				EnableTCPReset: enableTCPReset,
+				FrontendPort:   frontPort,
+			},
+			t: &network.LoadBalancingRulePropertiesFormat{
+				Protocol:       network.TransportProtocolTCP,
+				EnableTCPReset: enableTCPReset,
+				FrontendPort:   frontPort,
+			},
+			wantLb:   true,
+			expected: true,
+		},
+		{
+			s: &network.LoadBalancingRulePropertiesFormat{
+				Protocol:       network.TransportProtocolUDP,
+				EnableTCPReset: disableTCPReset,
+				FrontendPort:   frontPort,
+			},
+			t: &network.LoadBalancingRulePropertiesFormat{
+				Protocol:       network.TransportProtocolUDP,
+				EnableTCPReset: enableTCPReset,
+				FrontendPort:   frontPort,
+			},
+			wantLb:   true,
+			expected: true,
+		},
+	}
+
+	for _, tc := range testcases {
+		assert.Equal(t, tc.expected, equalLoadBalancingRulePropertiesFormat(tc.s, tc.t, tc.wantLb))
+	}
+}