feat: impl dynamic resolver backend type

internal/gatewayapi/backend.go

@@ -40,6 +40,16 @@
 }
 
 func validateBackend(backend *egv1a1.Backend) status.Error {
+	if backend.Spec.Type != nil &&
+		*backend.Spec.Type == egv1a1.BackendTypeDynamicResolver {
+		if len(backend.Spec.Endpoints) > 0 || len(backend.Spec.AppProtocols) > 0 {
+			return status.NewRouteStatusError(
+				fmt.Errorf("DynamicResolver type cannot have endpoints or appProtocols specified"),
+				status.RouteReasonInvalidBackendRef,
+			)
+		}
+	}
+
 	for _, ep := range backend.Spec.Endpoints {
 		if ep.FQDN != nil {
 			hostname := ep.FQDN.Hostname

internal/gatewayapi/route.go

@@ -212,6 +212,7 @@ func (t *Translator) processHTTPRouteRules(httpRoute *HTTPRouteContext, parentRe
 		destName := irRouteDestinationName(httpRoute, ruleIdx)
 		allDs := []*ir.DestinationSetting{}
 		failedProcessDestination := false
+		hasDynamicResolver := false
 
 		// process each backendRef, and calculate the destination settings for this rule
 		for i, backendRef := range rule.BackendRefs {
@@ -231,6 +232,11 @@ func (t *Translator) processHTTPRouteRules(httpRoute *HTTPRouteContext, parentRe
 				continue
 			}
 			allDs = append(allDs, ds)
+
+			// check if there is a dynamic resolver in the backendRefs
+			if ds.IsDynamicResolver {
+				hasDynamicResolver = true
+			}
 		}
 
 		// process each ir route
@@ -254,13 +260,28 @@ func (t *Translator) processHTTPRouteRules(httpRoute *HTTPRouteContext, parentRe
 				irRoute.DirectResponse = &ir.CustomResponse{
 					StatusCode: ptr.To(uint32(500)),
 				}
+				// A route can only have one destination if this destination is a dynamic resolver, because the behavior of
+				// multiple destinations with one being a dynamic resolver just doesn't make sense.
+			case hasDynamicResolver && len(rule.BackendRefs) > 1:
+				irRoute.DirectResponse = &ir.CustomResponse{
+					StatusCode: ptr.To(uint32(500)),
+				}
 			default:
 				destination.Name = destName
 				destination.Settings = allDs
 				irRoute.Destination = destination
 			}
 		}
 
+		if hasDynamicResolver && len(rule.BackendRefs) > 1 {
+			errs.Add(status.NewRouteStatusError(
+				fmt.Errorf(
+					"failed to process route rule %d: dynamic resolver is not supported for multiple backendRefs",
+					ruleIdx),
+				status.RouteReasonInvalidBackendRef,
+			))
+		}
+
 		// TODO handle:
 		//	- sum of weights for valid backend refs is 0
 		//	- etc.
@@ -1821,6 +1842,12 @@ func (t *Translator) processBackendDestinationSetting(
 	backend := resources.GetBackend(backendNamespace, string(backendRef.Name))
 	ds := &ir.DestinationSetting{Name: name}
 
+	// There is only one backend if it is a dynamic resolver
+	if backend.Spec.Type != nil && *backend.Spec.Type == egv1a1.BackendTypeDynamicResolver {
+		ds.IsDynamicResolver = true
+		return ds
+	}
+
 	for _, bep := range backend.Spec.Endpoints {
 		var irde *ir.DestinationEndpoint
 		switch {

internal/gatewayapi/testdata/httproute-dynamic-resolver-with-mutliple-backends.in.yaml

@@ -0,0 +1,54 @@
+gateways:
+- apiVersion: gateway.networking.k8s.io/v1
+  kind: Gateway
+  metadata:
+    namespace: envoy-gateway
+    name: gateway-1
+  spec:
+    gatewayClassName: envoy-gateway-class
+    listeners:
+    - name: http
+      protocol: HTTP
+      port: 80
+      allowedRoutes:
+        namespaces:
+          from: All
+httpRoutes:
+- apiVersion: gateway.networking.k8s.io/v1
+  kind: HTTPRoute
+  metadata:
+    namespace: default
+    name: httproute-1
+  spec:
+    hostnames:
+    - gateway.envoyproxy.io
+    parentRefs:
+    - namespace: envoy-gateway
+      name: gateway-1
+      sectionName: http
+    rules:
+    - backendRefs:
+      - group: gateway.envoyproxy.io
+        kind: Backend
+        name: backend-1
+      - group: gateway.envoyproxy.io
+        kind: Backend
+        name: backend-2
+backends:
+- apiVersion: gateway.envoyproxy.io/v1alpha1
+  kind: Backend
+  metadata:
+    name: backend-1
+    namespace: default
+  spec:
+    type: DynamicResolver
+- apiVersion: gateway.envoyproxy.io/v1alpha1
+  kind: Backend
+  metadata:
+    name: backend-2
+    namespace: default
+  spec:
+    endpoints:
+    - ip:
+        address: 1.1.1.1
+        port: 3001

internal/gatewayapi/testdata/httproute-dynamic-resolver-with-mutliple-backends.out.yaml

@@ -0,0 +1,167 @@
+backends:
+- apiVersion: gateway.envoyproxy.io/v1alpha1
+  kind: Backend
+  metadata:
+    creationTimestamp: null
+    name: backend-1
+    namespace: default
+  spec:
+    type: DynamicResolver
+  status:
+    conditions:
+    - lastTransitionTime: null
+      message: The Backend was accepted
+      reason: Accepted
+      status: "True"
+      type: Accepted
+- apiVersion: gateway.envoyproxy.io/v1alpha1
+  kind: Backend
+  metadata:
+    creationTimestamp: null
+    name: backend-2
+    namespace: default
+  spec:
+    endpoints:
+    - ip:
+        address: 1.1.1.1
+        port: 3001
+  status:
+    conditions:
+    - lastTransitionTime: null
+      message: The Backend was accepted
+      reason: Accepted
+      status: "True"
+      type: Accepted
+gateways:
+- apiVersion: gateway.networking.k8s.io/v1
+  kind: Gateway
+  metadata:
+    creationTimestamp: null
+    name: gateway-1
+    namespace: envoy-gateway
+  spec:
+    gatewayClassName: envoy-gateway-class
+    listeners:
+    - allowedRoutes:
+        namespaces:
+          from: All
+      name: http
+      port: 80
+      protocol: HTTP
+  status:
+    listeners:
+    - attachedRoutes: 1
+      conditions:
+      - lastTransitionTime: null
+        message: Sending translated listener configuration to the data plane
+        reason: Programmed
+        status: "True"
+        type: Programmed
+      - lastTransitionTime: null
+        message: Listener has been successfully translated
+        reason: Accepted
+        status: "True"
+        type: Accepted
+      - lastTransitionTime: null
+        message: Listener references have been resolved
+        reason: ResolvedRefs
+        status: "True"
+        type: ResolvedRefs
+      name: http
+      supportedKinds:
+      - group: gateway.networking.k8s.io
+        kind: HTTPRoute
+      - group: gateway.networking.k8s.io
+        kind: GRPCRoute
+httpRoutes:
+- apiVersion: gateway.networking.k8s.io/v1
+  kind: HTTPRoute
+  metadata:
+    creationTimestamp: null
+    name: httproute-1
+    namespace: default
+  spec:
+    hostnames:
+    - gateway.envoyproxy.io
+    parentRefs:
+    - name: gateway-1
+      namespace: envoy-gateway
+      sectionName: http
+    rules:
+    - backendRefs:
+      - group: gateway.envoyproxy.io
+        kind: Backend
+        name: backend-1
+      - group: gateway.envoyproxy.io
+        kind: Backend
+        name: backend-2
+  status:
+    parents:
+    - conditions:
+      - lastTransitionTime: null
+        message: Route is accepted
+        reason: Accepted
+        status: "True"
+        type: Accepted
+      - lastTransitionTime: null
+        message: 'Failed to process route rule 0: dynamic resolver is not supported
+          for multiple backendRefs.'
+        reason: InvalidBackendRef
+        status: "False"
+        type: ResolvedRefs
+      controllerName: gateway.envoyproxy.io/gatewayclass-controller
+      parentRef:
+        name: gateway-1
+        namespace: envoy-gateway
+        sectionName: http
+infraIR:
+  envoy-gateway/gateway-1:
+    proxy:
+      listeners:
+      - address: null
+        name: envoy-gateway/gateway-1/http
+        ports:
+        - containerPort: 10080
+          name: http-80
+          protocol: HTTP
+          servicePort: 80
+      metadata:
+        labels:
+          gateway.envoyproxy.io/owning-gateway-name: gateway-1
+          gateway.envoyproxy.io/owning-gateway-namespace: envoy-gateway
+      name: envoy-gateway/gateway-1
+xdsIR:
+  envoy-gateway/gateway-1:
+    accessLog:
+      json:
+      - path: /dev/stdout
+    http:
+    - address: 0.0.0.0
+      hostnames:
+      - '*'
+      isHTTP2: false
+      metadata:
+        kind: Gateway
+        name: gateway-1
+        namespace: envoy-gateway
+        sectionName: http
+      name: envoy-gateway/gateway-1/http
+      path:
+        escapedSlashesAction: UnescapeAndRedirect
+        mergeSlashes: true
+      port: 10080
+      routes:
+      - directResponse:
+          statusCode: 500
+        hostname: gateway.envoyproxy.io
+        isHTTP2: false
+        metadata:
+          kind: HTTPRoute
+          name: httproute-1
+          namespace: default
+        name: httproute/default/httproute-1/rule/0/match/-1/gateway_envoyproxy_io
+    readyListener:
+      address: 0.0.0.0
+      ipFamily: IPv4
+      path: /ready
+      port: 19003

internal/gatewayapi/testdata/httproute-dynamic-resolver.in.yaml

@@ -0,0 +1,41 @@
+gateways:
+- apiVersion: gateway.networking.k8s.io/v1
+  kind: Gateway
+  metadata:
+    namespace: envoy-gateway
+    name: gateway-1
+  spec:
+    gatewayClassName: envoy-gateway-class
+    listeners:
+    - name: http
+      protocol: HTTP
+      port: 80
+      allowedRoutes:
+        namespaces:
+          from: All
+httpRoutes:
+- apiVersion: gateway.networking.k8s.io/v1
+  kind: HTTPRoute
+  metadata:
+    namespace: default
+    name: httproute-1
+  spec:
+    hostnames:
+    - gateway.envoyproxy.io
+    parentRefs:
+    - namespace: envoy-gateway
+      name: gateway-1
+      sectionName: http
+    rules:
+    - backendRefs:
+      - group: gateway.envoyproxy.io
+        kind: Backend
+        name: backend-1
+backends:
+- apiVersion: gateway.envoyproxy.io/v1alpha1
+  kind: Backend
+  metadata:
+    name: backend-1
+    namespace: default
+  spec:
+    type: DynamicResolver