envoy/cds: add nil check for ConnectionSettings (#4821)

With the addition of rate limiting to the
UpstreamTrafficSetting spec, it is possible
for the UpstreamTrafficSetting object to be non
nil while having its ConnectionSettings as nil.
Add nil check so the code doesn't panic when
ConnectionSettings is nil and RateLimit is configured.

Signed-off-by: Shashank Ram <shashr2204@gmail.com>

pkg/envoy/cds/cluster.go

@@ -394,7 +394,7 @@ func applyUpstreamTrafficSetting(upstreamTrafficSetting *policyv1alpha1.Upstream
 		Thresholds: []*xds_cluster.CircuitBreakers_Thresholds{threshold},
 	}
 
-	if upstreamTrafficSetting == nil {
+	if upstreamTrafficSetting == nil || upstreamTrafficSetting.Spec.ConnectionSettings == nil {
 		return
 	}
 

pkg/envoy/cds/cluster_test.go

@@ -91,6 +91,16 @@ func TestGetUpstreamServiceCluster(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "Cluster without circuit breaker but with valid UpstreamTrafficSetting should not error/panic",
+			clusterConfig: trafficpolicy.MeshClusterConfig{
+				Name:    "default/bookstore-v1_14001",
+				Service: upstreamSvc,
+				UpstreamTrafficSetting: &policyv1alpha1.UpstreamTrafficSetting{
+					Spec: policyv1alpha1.UpstreamTrafficSettingSpec{},
+				},
+			},
+		},
 	}
 
 	for _, tc := range testCases {
@@ -106,7 +116,7 @@ func TestGetUpstreamServiceCluster(t *testing.T) {
 				assert.Nil(remoteCluster.HealthChecks)
 			}
 
-			if tc.clusterConfig.UpstreamTrafficSetting != nil {
+			if tc.expectedCircuitBreakerThreshold != nil {
 				assert.Equal(tc.expectedCircuitBreakerThreshold, remoteCluster.CircuitBreakers)
 			}
 		})