Feature: allow mixed IP and UDS endpoints in backend route references

internal/gatewayapi/listener.go

@@ -950,7 +950,7 @@ func (t *Translator) processBackendRefs(name string, backendCluster egv1a1.Backe
 			}
 			result = append(result, ds)
 		case resource.KindBackend:
-			if err := t.validateBackendRefBackend(ref.BackendObjectReference, resources, ns, true); err != nil {
+			if err := t.validateBackendRefBackend(ref.BackendObjectReference, resources, ns); err != nil {
 				return nil, nil, err
 			}
 			ds := t.processBackendDestinationSetting(name, ref.BackendObjectReference, ns, ir.TCP)

internal/gatewayapi/route.go

@@ -1957,7 +1957,7 @@ func validateDestinationSettings(destinationSettings *ir.DestinationSetting, isS
 	case egv1a1.KindBackend:
 		if destinationSettings.AddressType != nil && *destinationSettings.AddressType == ir.MIXED {
 			return status.NewRouteStatusError(
-				fmt.Errorf("mixed FQDN and IP or Unix address type for the same backendRef is not supported"),
+				fmt.Errorf("mixed FQDN with IP or Unix address type for the same backendRef is not supported"),
 				status.RouteReasonUnsupportedAddressType)
 		}
 	case resource.KindService, resource.KindServiceImport:
@@ -2505,7 +2505,14 @@ func (t *Translator) processBackendDestinationSetting(
 	}
 
 	if len(addrTypeMap) > 0 && dstAddrType == nil {
-		dstAddrType = ptr.To(ir.MIXED)
+		// IP + UDS mixing is supported by Envoy (both are static endpoint types).
+		// Only classify as MIXED when FQDN is involved, which requires different
+		// cluster resolution and cannot share a cluster with IP/UDS endpoints.
+		if len(addrTypeMap) == 2 && addrTypeMap[ir.IP] > 0 && addrTypeMap[ir.UDS] > 0 {
+			dstAddrType = ptr.To(ir.IP)
+		} else {
+			dstAddrType = ptr.To(ir.MIXED)
+		}
 	}
 
 	ds.Endpoints = dstEndpoints

internal/gatewayapi/route_test.go

@@ -376,6 +376,37 @@ func TestValidateDestinationSettings(t *testing.T) {
 			wantErr:                 true,
 			wantReason:              status.RouteReasonUnsupportedAddressType,
 		},
+		{
+			name: "mixed FQDN address type rejected for Backend",
+			ds: &ir.DestinationSetting{
+				Name:        "mixed-fqdn",
+				Endpoints:   []*ir.DestinationEndpoint{{Host: "10.0.0.1"}},
+				AddressType: ptr.To(ir.MIXED),
+			},
+			kind:       ptr.To(gwapiv1.Kind(egv1a1.KindBackend)),
+			wantErr:    true,
+			wantReason: status.RouteReasonUnsupportedAddressType,
+		},
+		{
+			name: "IP address type allowed for Backend",
+			ds: &ir.DestinationSetting{
+				Name:        "ip-only",
+				Endpoints:   []*ir.DestinationEndpoint{{Host: "10.0.0.1"}},
+				AddressType: ptr.To(ir.IP),
+			},
+			kind:    ptr.To(gwapiv1.Kind(egv1a1.KindBackend)),
+			wantErr: false,
+		},
+		{
+			name: "UDS address type allowed for Backend",
+			ds: &ir.DestinationSetting{
+				Name:        "uds-only",
+				Endpoints:   []*ir.DestinationEndpoint{{Path: ptr.To("/var/run/backend.sock")}},
+				AddressType: ptr.To(ir.UDS),
+			},
+			kind:    ptr.To(gwapiv1.Kind(egv1a1.KindBackend)),
+			wantErr: false,
+		},
 	}
 
 	for _, tt := range tests {

internal/gatewayapi/testdata/httproute-attaching-to-listener-with-backend-backendref-host-infra.out.yaml

@@ -151,10 +151,9 @@ httpRoutes:
         status: "True"
         type: Accepted
       - lastTransitionTime: null
-        message: 'Failed to process route rule 0 backendRef 0: unix domain sockets
-          are not supported in backend references.'
-        reason: UnsupportedAddressType
-        status: "False"
+        message: Resolved all the Object references for the Route
+        reason: ResolvedRefs
+        status: "True"
         type: ResolvedRefs
       controllerName: gateway.envoyproxy.io/gatewayclass-controller
       parentRef:
@@ -366,8 +365,25 @@ xdsIR:
         mergeSlashes: true
       port: 80
       routes:
-      - directResponse:
-          statusCode: 500
+      - destination:
+          metadata:
+            kind: HTTPRoute
+            name: httproute-1
+            namespace: default
+          name: httproute/default/httproute-1/rule/0
+          settings:
+          - addressType: UDS
+            endpoints:
+            - host: ""
+              path: /var/run/backend.sock
+              port: 0
+            metadata:
+              kind: Backend
+              name: backend-uds
+              namespace: default
+            name: httproute/default/httproute-1/rule/0/backend/0
+            protocol: HTTP
+            weight: 1
         hostname: '*'
         isHTTP2: false
         metadata:

internal/gatewayapi/testdata/httproute-attaching-to-listener-with-backend-backendref-mixed-address-type.out.yaml

@@ -145,10 +145,9 @@ httpRoutes:
         status: "True"
         type: Accepted
       - lastTransitionTime: null
-        message: 'Failed to process route rule 0 backendRef 0: unix domain sockets
-          are not supported in backend references.'
-        reason: UnsupportedAddressType
-        status: "False"
+        message: Resolved all the Object references for the Route
+        reason: ResolvedRefs
+        status: "True"
         type: ResolvedRefs
       controllerName: gateway.envoyproxy.io/gatewayclass-controller
       parentRef:
@@ -182,8 +181,8 @@ httpRoutes:
         status: "True"
         type: Accepted
       - lastTransitionTime: null
-        message: 'Failed to process route rule 0 backendRef 0: mixed FQDN and IP or
-          Unix address type for the same backendRef is not supported.'
+        message: 'Failed to process route rule 0 backendRef 0: mixed FQDN with IP
+          or Unix address type for the same backendRef is not supported.'
         reason: UnsupportedAddressType
         status: "False"
         type: ResolvedRefs
@@ -219,8 +218,8 @@ httpRoutes:
         status: "True"
         type: Accepted
       - lastTransitionTime: null
-        message: 'Failed to process route rule 0 backendRef 0: mixed FQDN and IP or
-          Unix address type for the same backendRef is not supported.'
+        message: 'Failed to process route rule 0 backendRef 0: mixed FQDN with IP
+          or Unix address type for the same backendRef is not supported.'
         reason: UnsupportedAddressType
         status: "False"
         type: ResolvedRefs
@@ -290,8 +289,27 @@ xdsIR:
         mergeSlashes: true
       port: 10080
       routes:
-      - directResponse:
-          statusCode: 500
+      - destination:
+          metadata:
+            kind: HTTPRoute
+            name: httproute-1
+            namespace: default
+          name: httproute/default/httproute-1/rule/0
+          settings:
+          - addressType: IP
+            endpoints:
+            - host: ""
+              path: /var/run/backend.sock
+              port: 0
+            - host: 1.1.1.1
+              port: 3001
+            metadata:
+              kind: Backend
+              name: backend-ip-uds-mixed
+              namespace: default
+            name: httproute/default/httproute-1/rule/0/backend/0
+            protocol: HTTP
+            weight: 1
         hostname: '*'
         isHTTP2: false
         metadata:

internal/gatewayapi/testdata/httproute-attaching-to-listener-with-backend-backendref.out.yaml

@@ -153,10 +153,9 @@ httpRoutes:
         status: "True"
         type: Accepted
       - lastTransitionTime: null
-        message: 'Failed to process route rule 0 backendRef 0: unix domain sockets
-          are not supported in backend references.'
-        reason: UnsupportedAddressType
-        status: "False"
+        message: Resolved all the Object references for the Route
+        reason: ResolvedRefs
+        status: "True"
         type: ResolvedRefs
       controllerName: gateway.envoyproxy.io/gatewayclass-controller
       parentRef:
@@ -370,8 +369,25 @@ xdsIR:
         mergeSlashes: true
       port: 10080
       routes:
-      - directResponse:
-          statusCode: 500
+      - destination:
+          metadata:
+            kind: HTTPRoute
+            name: httproute-1
+            namespace: default
+          name: httproute/default/httproute-1/rule/0
+          settings:
+          - addressType: UDS
+            endpoints:
+            - host: ""
+              path: /var/run/backend.sock
+              port: 0
+            metadata:
+              kind: Backend
+              name: backend-uds
+              namespace: default
+            name: httproute/default/httproute-1/rule/0/backend/0
+            protocol: HTTP
+            weight: 1
         hostname: '*'
         isHTTP2: false
         metadata:

internal/gatewayapi/testdata/httproute-attaching-to-listener-with-multiple-backend-backendrefs-diff-address-type.out.yaml

@@ -123,10 +123,9 @@ httpRoutes:
         status: "True"
         type: Accepted
       - lastTransitionTime: null
-        message: 'Failed to process route rule 0 backendRef 0: unix domain sockets
-          are not supported in backend references.'
-        reason: UnsupportedAddressType
-        status: "False"
+        message: Resolved all the Object references for the Route
+        reason: ResolvedRefs
+        status: "True"
         type: ResolvedRefs
       controllerName: gateway.envoyproxy.io/gatewayclass-controller
       parentRef:
@@ -163,10 +162,9 @@ httpRoutes:
         status: "True"
         type: Accepted
       - lastTransitionTime: null
-        message: 'Failed to process route rule 0 backendRef 0: unix domain sockets
-          are not supported in backend references.'
-        reason: UnsupportedAddressType
-        status: "False"
+        message: Resolved all the Object references for the Route
+        reason: ResolvedRefs
+        status: "True"
         type: ResolvedRefs
       controllerName: gateway.envoyproxy.io/gatewayclass-controller
       parentRef:
@@ -242,10 +240,9 @@ httpRoutes:
         status: "True"
         type: Accepted
       - lastTransitionTime: null
-        message: 'Failed to process route rule 0 backendRef 0: unix domain sockets
-          are not supported in backend references.'
-        reason: UnsupportedAddressType
-        status: "False"
+        message: Resolved all the Object references for the Route
+        reason: ResolvedRefs
+        status: "True"
         type: ResolvedRefs
       controllerName: gateway.envoyproxy.io/gatewayclass-controller
       parentRef:
@@ -320,8 +317,17 @@ xdsIR:
             namespace: default
           name: httproute/default/httproute-1/rule/0
           settings:
-          - invalid: true
+          - addressType: UDS
+            endpoints:
+            - host: ""
+              path: /var/run/backend.sock
+              port: 0
+            metadata:
+              kind: Backend
+              name: backend-uds
+              namespace: default
             name: httproute/default/httproute-1/rule/0/backend/0
+            protocol: HTTP
             weight: 1
           - addressType: IP
             endpoints:
@@ -363,8 +369,17 @@ xdsIR:
             namespace: default
           name: httproute/default/httproute-2/rule/0
           settings:
-          - invalid: true
+          - addressType: UDS
+            endpoints:
+            - host: ""
+              path: /var/run/backend.sock
+              port: 0
+            metadata:
+              kind: Backend
+              name: backend-uds
+              namespace: default
             name: httproute/default/httproute-2/rule/0/backend/0
+            protocol: HTTP
             weight: 1
           - addressType: IP
             endpoints:
@@ -435,8 +450,17 @@ xdsIR:
             namespace: default
           name: httproute/default/httproute-3/rule/0
           settings:
-          - invalid: true
+          - addressType: UDS
+            endpoints:
+            - host: ""
+              path: /var/run/backend.sock
+              port: 0
+            metadata:
+              kind: Backend
+              name: backend-uds
+              namespace: default
             name: httproute/default/httproute-3/rule/0/backend/0
+            protocol: HTTP
             weight: 1
           - addressType: FQDN
             endpoints:

internal/gatewayapi/testdata/httproute-attaching-to-listener-with-multiple-backend-backendrefs-same-address-type.out.yaml

@@ -170,11 +170,9 @@ httpRoutes:
         status: "True"
         type: Accepted
       - lastTransitionTime: null
-        message: |-
-          Failed to process route rule 0 backendRef 0: unix domain sockets are not supported in backend references.
-          Failed to process route rule 0 backendRef 1: unix domain sockets are not supported in backend references.
-        reason: UnsupportedAddressType
-        status: "False"
+        message: Resolved all the Object references for the Route
+        reason: ResolvedRefs
+        status: "True"
         type: ResolvedRefs
       controllerName: gateway.envoyproxy.io/gatewayclass-controller
       parentRef:
@@ -320,8 +318,37 @@ xdsIR:
         mergeSlashes: true
       port: 10080
       routes:
-      - directResponse:
-          statusCode: 500
+      - destination:
+          metadata:
+            kind: HTTPRoute
+            name: httproute-1
+            namespace: default
+          name: httproute/default/httproute-1/rule/0
+          settings:
+          - addressType: UDS
+            endpoints:
+            - host: ""
+              path: /var/run/backend.sock
+              port: 0
+            metadata:
+              kind: Backend
+              name: backend-uds
+              namespace: default
+            name: httproute/default/httproute-1/rule/0/backend/0
+            protocol: HTTP
+            weight: 1
+          - addressType: UDS
+            endpoints:
+            - host: ""
+              path: /var/run/backend2.sock
+              port: 0
+            metadata:
+              kind: Backend
+              name: backend-uds2
+              namespace: default
+            name: httproute/default/httproute-1/rule/0/backend/1
+            protocol: HTTP
+            weight: 1
         hostname: '*'
         isHTTP2: false
         metadata: