Controller: Fix panic in alternative backend merging. (#11794)

Co-authored-by: joey <zchengjoey@gmail.com>

internal/ingress/controller/controller.go

@@ -1594,7 +1594,11 @@ func mergeAlternativeBackends(ing *ingress.Ingress, upstreams map[string]*ingres
 			altEqualsPri := false
 
 			for _, loc := range servers[defServerName].Locations {
-				priUps := upstreams[loc.Backend]
+				priUps, ok := upstreams[loc.Backend]
+				if !ok {
+					klog.Warningf("cannot find primary backend %s for location %s%s", loc.Backend, servers[defServerName].Hostname, loc.Path)
+					continue
+				}
 				altEqualsPri = altUps.Name == priUps.Name
 				if altEqualsPri {
 					klog.Warningf("alternative upstream %s in Ingress %s/%s is primary upstream in Other Ingress for location %s%s!",
@@ -1653,7 +1657,11 @@ func mergeAlternativeBackends(ing *ingress.Ingress, upstreams map[string]*ingres
 
 			// find matching paths
 			for _, loc := range server.Locations {
-				priUps := upstreams[loc.Backend]
+				priUps, ok := upstreams[loc.Backend]
+				if !ok {
+					klog.Warningf("cannot find primary backend %s for location %s%s", loc.Backend, server.Hostname, loc.Path)
+					continue
+				}
 				altEqualsPri = altUps.Name == priUps.Name
 				if altEqualsPri {
 					klog.Warningf("alternative upstream %s in Ingress %s/%s is primary upstream in Other Ingress for location %s%s!",

internal/ingress/controller/controller_test.go

@@ -1292,6 +1292,74 @@ func TestMergeAlternativeBackends(t *testing.T) {
 				},
 			},
 		},
+		"alternative backend does not merge for missing upstream": {
+			&ingress.Ingress{
+				Ingress: networking.Ingress{
+					ObjectMeta: metav1.ObjectMeta{
+						Namespace: "example",
+					},
+					Spec: networking.IngressSpec{
+						Rules: []networking.IngressRule{
+							{
+								Host: "example.com",
+								IngressRuleValue: networking.IngressRuleValue{
+									HTTP: &networking.HTTPIngressRuleValue{
+										Paths: []networking.HTTPIngressPath{
+											{
+												Path:     "/",
+												PathType: &pathTypePrefix,
+												Backend: networking.IngressBackend{
+													Service: &networking.IngressServiceBackend{
+														Name: "http-svc-canary",
+														Port: networking.ServiceBackendPort{
+															Number: 80,
+														},
+													},
+												},
+											},
+										},
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			map[string]*ingress.Backend{
+				"example-http-svc-canary-80": {
+					Name:     "example-http-svc-canary-80",
+					NoServer: true,
+					TrafficShapingPolicy: ingress.TrafficShapingPolicy{
+						Weight: 20,
+					},
+				},
+			},
+			map[string]*ingress.Server{
+				"example.com": {
+					Hostname: "example.com",
+					Locations: []*ingress.Location{
+						{
+							Path:     "/",
+							PathType: &pathTypePrefix,
+							Backend:  "example-http-svc-80",
+						},
+					},
+				},
+			},
+			map[string]*ingress.Backend{},
+			map[string]*ingress.Server{
+				"example.com": {
+					Hostname: "example.com",
+					Locations: []*ingress.Location{
+						{
+							Path:     "/",
+							PathType: &pathTypePrefix,
+							Backend:  "example-http-svc-80",
+						},
+					},
+				},
+			},
+		},
 	}
 
 	for title, tc := range testCases {