Return apiserver addresses from both etcd and endpoints

pkg/server/router.go

@@ -19,6 +19,7 @@ import (
 	"github.com/k3s-io/k3s/pkg/bootstrap"
 	"github.com/k3s-io/k3s/pkg/cli/cmds"
 	"github.com/k3s-io/k3s/pkg/daemons/config"
+	"github.com/k3s-io/k3s/pkg/etcd"
 	"github.com/k3s-io/k3s/pkg/nodepassword"
 	"github.com/k3s-io/k3s/pkg/server/auth"
 	"github.com/k3s-io/k3s/pkg/util"
@@ -31,6 +32,7 @@ import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/types"
 	"k8s.io/apimachinery/pkg/util/json"
+	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/apimachinery/pkg/util/wait"
 	"k8s.io/apiserver/pkg/authentication/user"
 	"k8s.io/apiserver/pkg/endpoints/request"
@@ -305,22 +307,15 @@ func fileHandler(fileName ...string) http.Handler {
 	})
 }
 
+// apiserversHandler returns a list of apiserver addresses.
+// It attempts to merge results from both the apiserver and directly from etcd,
+// in case we are recovering from an apiserver outage that rendered the endpoint list unavailable.
 func apiserversHandler(server *config.Control) http.Handler {
-	var endpointsClient typedcorev1.EndpointsInterface
+	collectAddresses := getAddressCollector(server)
 	return http.HandlerFunc(func(resp http.ResponseWriter, req *http.Request) {
-		ctx := req.Context()
-		var endpoints []string
-		if endpointsClient == nil {
-			if server.Runtime.Core != nil {
-				endpointsClient = server.Runtime.K8s.CoreV1().Endpoints(metav1.NamespaceDefault)
-			}
-		}
-		if endpointsClient != nil {
-			if endpoint, _ := endpointsClient.Get(ctx, "kubernetes", metav1.GetOptions{}); endpoint != nil {
-				endpoints = util.GetAddresses(endpoint)
-			}
-		}
-
+		ctx, cancel := context.WithTimeout(req.Context(), 5*time.Second)
+		defer cancel()
+		endpoints := collectAddresses(ctx)
 		resp.Header().Set("content-type", "application/json")
 		if err := json.NewEncoder(resp).Encode(endpoints); err != nil {
 			util.SendError(errors.Wrap(err, "failed to encode apiserver endpoints"), resp, req, http.StatusInternalServerError)
@@ -526,3 +521,75 @@ func ensureSecret(ctx context.Context, config *Config, node *nodeInfo) {
 		return false, nil
 	})
 }
+
+// addressGetter is a common signature for functions that return an address channel
+type addressGetter func(ctx context.Context) <-chan []string
+
+// kubernetesGetter returns a function that returns a channel that can be read to get apiserver addresses from kubernetes endpoints
+func kubernetesGetter(server *config.Control) addressGetter {
+	var endpointsClient typedcorev1.EndpointsInterface
+	return func(ctx context.Context) <-chan []string {
+		ch := make(chan []string, 1)
+		go func() {
+			if endpointsClient == nil {
+				if server.Runtime.K8s != nil {
+					endpointsClient = server.Runtime.K8s.CoreV1().Endpoints(metav1.NamespaceDefault)
+				}
+			}
+			if endpointsClient != nil {
+				if endpoint, err := endpointsClient.Get(ctx, "kubernetes", metav1.GetOptions{}); err != nil {
+					logrus.Debugf("Failed to get apiserver addresses from kubernetes: %v", err)
+				} else {
+					ch <- util.GetAddresses(endpoint)
+				}
+			}
+			close(ch)
+		}()
+		return ch
+	}
+}
+
+// etcdGetter returns a function that returns a channel that can be read to get apiserver addresses from etcd
+func etcdGetter(server *config.Control) addressGetter {
+	return func(ctx context.Context) <-chan []string {
+		ch := make(chan []string, 1)
+		go func() {
+			if addresses, err := etcd.GetAPIServerURLsFromETCD(ctx, server); err != nil {
+				logrus.Debugf("Failed to get apiserver addresses from etcd: %v", err)
+			} else {
+				ch <- addresses
+			}
+			close(ch)
+		}()
+		return ch
+	}
+}
+
+// getAddressCollector returns a function that can be called to return
+// apiserver addresses from both kubernetes and etcd
+func getAddressCollector(server *config.Control) func(ctx context.Context) []string {
+	getFromKubernetes := kubernetesGetter(server)
+	getFromEtcd := etcdGetter(server)
+
+	// read from both kubernetes and etcd in parallel, returning the collected results
+	return func(ctx context.Context) []string {
+		a := sets.Set[string]{}
+		r := []string{}
+		k8sCh := getFromKubernetes(ctx)
+		k8sOk := true
+		etcdCh := getFromEtcd(ctx)
+		etcdOk := true
+
+		for k8sOk || etcdOk {
+			select {
+			case r, k8sOk = <-k8sCh:
+				a.Insert(r...)
+			case r, etcdOk = <-etcdCh:
+				a.Insert(r...)
+			case <-ctx.Done():
+				return a.UnsortedList()
+			}
+		}
+		return a.UnsortedList()
+	}
+}