dataclients/kubernetes: add metadata route

Adds a special route with a predefined id `kube__metadata`
that contains `False` predicate and no filters.

The first argument of `False` predicate (which it ignores anyway)
contains endpoint metadata encoded as JSON.

Example (formatted):
```
kube__metadata: False("{
\"addresses\":[
  {
    \"address\":\"1.2.3.4\",
    \"zone\":\"zoneA\",
    \"nodeName\":\"node1\",
    \"targetRef\":{
      \"kind\":\"Pod\",
      \"name\":\"foo-app\",
      \"namespace\":\"default\",
      \"uid\":\"83a6408f-8a5b-405c-93f4-1199f7712956\"
    }
  },
  ...
]")
```

This route could be used to obtain zone, node and pod names for a given address.
E.g. EndpointRegistry postprocessor may check this route and store zone, node and pod name for each endpoint.

TODO:
- [ ] add flag  to enable metadata route
- [ ] tests

Fixes #1559

Signed-off-by: Alexander Yastrebov <[email protected]>

dataclients/kubernetes/clusterclient.go

@@ -519,16 +519,13 @@ func (c *clusterClient) loadEndpointSlices() (map[definitions.ResourceID]*skippe
 					// we should delete it, because of eventual consistency
 					// it is actually terminating
 					delete(resEps, address)
-				} else if ep.Conditions == nil {
+				} else if ep.Conditions == nil || ep.isReady() {
 					// if conditions are nil then we need to treat is as ready
 					resEps[address] = &skipperEndpoint{
-						Address: address,
-						Zone:    ep.Zone,
-					}
-				} else if ep.isReady() {
-					resEps[address] = &skipperEndpoint{
-						Address: address,
-						Zone:    ep.Zone,
+						Address:   address,
+						Zone:      ep.Zone,
+						NodeName:  ep.NodeName,
+						TargetRef: ep.TargetRef,
 					}
 				}
 			}

dataclients/kubernetes/endpoints.go

@@ -98,8 +98,9 @@ type subset struct {
 }
 
 type address struct {
-	IP   string `json:"ip"`
-	Node string `json:"nodeName"`
+	IP        string           `json:"ip"`
+	NodeName  string           `json:"nodeName"`
+	TargetRef *objectReference `json:"targetRef"`
 }
 
 type port struct {

dataclients/kubernetes/endpointslices.go

@@ -16,8 +16,10 @@ type skipperEndpointSlice struct {
 
 // Conditions have to be evaluated before creation
 type skipperEndpoint struct {
-	Address string
-	Zone    string
+	Address   string
+	Zone      string
+	NodeName  string
+	TargetRef *objectReference
 }
 
 func (eps *skipperEndpointSlice) getPort(protocol, pName string, pValue int) int {
@@ -125,6 +127,10 @@ type EndpointSliceEndpoints struct {
 	// https://kubernetes.io/docs/concepts/services-networking/topology-aware-routing/#safeguards
 	// Zone aware routing will be available if https://github.com/zalando/skipper/issues/1446 is closed.
 	Zone string `json:"zone"` // "eu-central-1c"
+	// Node hosting this endpoint. This can be used to determine endpoints local to a node.
+	NodeName string `json:"nodeName"`
+	// TargetRef is a reference to a Kubernetes object that represents this endpoint.
+	TargetRef *objectReference `json:"targetRef"`
 }
 
 type endpointsliceCondition struct {

dataclients/kubernetes/kube.go

@@ -2,13 +2,13 @@ package kubernetes
 
 import (
 	"fmt"
+	"html/template"
 	"net"
 	"net/http"
 	"os"
 	"regexp"
 	"strings"
 	"sync"
-	"text/template"
 	"time"
 
 	log "github.com/sirupsen/logrus"
@@ -18,7 +18,10 @@ import (
 	"github.com/zalando/skipper/secrets/certregistry"
 )
 
-const DefaultLoadBalancerAlgorithm = "roundRobin"
+const (
+	DefaultLoadBalancerAlgorithm = "roundRobin"
+	MetadataRouteID              = "kube__metadata"
+)
 
 const (
 	defaultIngressClass    = "skipper"
@@ -437,6 +440,10 @@ func (c *Client) loadAndConvert() ([]*eskip.Route, error) {
 		r = append(r, globalRedirectRoute(c.httpsRedirectCode))
 	}
 
+	if false { // TODO: flag
+		r = append(r, metadataRoute(state))
+	}
+
 	return r, nil
 }
 

dataclients/kubernetes/kube_test.go

@@ -86,8 +86,8 @@ func testEndpoints(namespace, name string, labels map[string]string, base string
 
 		for i := 0; i < n; i++ {
 			adr := &address{
-				IP:   fmt.Sprintf("%s.%d", base, i),
-				Node: fmt.Sprintf("node-%d", i),
+				IP:       fmt.Sprintf("%s.%d", base, i),
+				NodeName: fmt.Sprintf("node-%d", i),
 			}
 			s.Addresses = append(s.Addresses, adr)
 		}

dataclients/kubernetes/metadataroute.go

@@ -0,0 +1,61 @@
+package kubernetes
+
+import (
+	"encoding/json"
+	"strings"
+
+	"github.com/zalando/skipper/eskip"
+	"github.com/zalando/skipper/predicates"
+)
+
+type kubeRouteMetadata struct {
+	Addresses []kubeRouteMetadataAddress `json:"addresses"`
+}
+
+type kubeRouteMetadataAddress struct {
+	Address   string           `json:"address"`
+	Zone      string           `json:"zone"`
+	NodeName  string           `json:"nodeName"`
+	TargetRef *objectReference `json:"targetRef"`
+}
+
+// metadataRoute creates a route with [MetadataRouteID] id that matches no requests and
+// contains metadata for each endpoint address used by Ingresses and RouteGroups.
+func metadataRoute(s *clusterState) *eskip.Route {
+	var metadata kubeRouteMetadata
+	for id := range s.cachedEndpoints {
+		if s.enableEndpointSlices {
+			if eps, ok := s.endpointSlices[id.ResourceID]; ok {
+				for _, ep := range eps.Endpoints {
+					metadata.Addresses = append(metadata.Addresses, kubeRouteMetadataAddress{
+						Address:   ep.Address,
+						Zone:      ep.Zone,
+						NodeName:  ep.NodeName,
+						TargetRef: ep.TargetRef,
+					})
+				}
+			}
+		} else {
+			if ep, ok := s.endpoints[id.ResourceID]; ok {
+				for _, subset := range ep.Subsets {
+					for _, addr := range subset.Addresses {
+						metadata.Addresses = append(metadata.Addresses, kubeRouteMetadataAddress{
+							Address:   addr.IP,
+							NodeName:  addr.NodeName,
+							TargetRef: addr.TargetRef,
+						})
+					}
+				}
+			}
+		}
+	}
+
+	var b strings.Builder
+	_ = json.NewEncoder(&b).Encode(&metadata)
+
+	return &eskip.Route{
+		Id:          MetadataRouteID,
+		Predicates:  []*eskip.Predicate{{Name: predicates.FalseName, Args: []any{b.String()}}},
+		BackendType: eskip.ShuntBackend,
+	}
+}

dataclients/kubernetes/resources.go

@@ -24,3 +24,10 @@ type secret struct {
 type secretList struct {
 	Items []*secret `json:"items"`
 }
+
+type objectReference struct {
+	Kind      string `json:"kind"`
+	Name      string `json:"name"`
+	Namespace string `json:"namespace"`
+	Uid       string `json:"uid"`
+}