Use actual etcd client for /healthz/etcd checks

staging/src/k8s.io/apiserver/pkg/server/options/BUILD

@@ -52,8 +52,8 @@ go_library(
         "//vendor/k8s.io/apiserver/pkg/server/healthz:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/server/resourceconfig:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/server/storage:go_default_library",
-        "//vendor/k8s.io/apiserver/pkg/storage/etcd3/preflight:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/storage/storagebackend:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/storage/storagebackend/factory:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/util/feature:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/util/flag:go_default_library",
         "//vendor/k8s.io/apiserver/plugin/pkg/audit/buffered:go_default_library",

staging/src/k8s.io/apiserver/pkg/server/options/etcd.go

@@ -32,8 +32,8 @@ import (
 	"k8s.io/apiserver/pkg/server"
 	"k8s.io/apiserver/pkg/server/healthz"
 	serverstorage "k8s.io/apiserver/pkg/server/storage"
-	"k8s.io/apiserver/pkg/storage/etcd3/preflight"
 	"k8s.io/apiserver/pkg/storage/storagebackend"
+	storagefactory "k8s.io/apiserver/pkg/storage/storagebackend/factory"
 )
 
 type EtcdOptions struct {
@@ -181,29 +181,30 @@ func (s *EtcdOptions) ApplyTo(c *server.Config) error {
 	if s == nil {
 		return nil
 	}
-
-	s.addEtcdHealthEndpoint(c)
+	if err := s.addEtcdHealthEndpoint(c); err != nil {
+		return err
+	}
 	c.RESTOptionsGetter = &SimpleRestOptionsFactory{Options: *s}
 	return nil
 }
 
 func (s *EtcdOptions) ApplyWithStorageFactoryTo(factory serverstorage.StorageFactory, c *server.Config) error {
-	s.addEtcdHealthEndpoint(c)
+	if err := s.addEtcdHealthEndpoint(c); err != nil {
+		return err
+	}
 	c.RESTOptionsGetter = &storageFactoryRestOptionsFactory{Options: *s, StorageFactory: factory}
 	return nil
 }
 
-func (s *EtcdOptions) addEtcdHealthEndpoint(c *server.Config) {
+func (s *EtcdOptions) addEtcdHealthEndpoint(c *server.Config) error {
+	healthCheck, err := storagefactory.CreateHealthCheck(s.StorageConfig)
+	if err != nil {
+		return err
+	}
 	c.HealthzChecks = append(c.HealthzChecks, healthz.NamedCheck("etcd", func(r *http.Request) error {
-		done, err := preflight.EtcdConnection{ServerList: s.StorageConfig.ServerList}.CheckEtcdServers()
-		if !done {
-			return fmt.Errorf("etcd failed")
-		}
-		if err != nil {
-			return err
-		}
-		return nil
+		return healthCheck()
 	}))
+	return nil
 }
 
 type SimpleRestOptionsFactory struct {

staging/src/k8s.io/apiserver/pkg/storage/storagebackend/factory/BUILD

@@ -37,6 +37,7 @@ go_library(
         "//vendor/github.com/coreos/etcd/clientv3:go_default_library",
         "//vendor/github.com/coreos/etcd/pkg/transport:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/util/net:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/util/wait:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/storage:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/storage/etcd:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/storage/etcd3:go_default_library",

staging/src/k8s.io/apiserver/pkg/storage/storagebackend/factory/etcd2.go

@@ -17,6 +17,8 @@ limitations under the License.
 package factory
 
 import (
+	"context"
+	"fmt"
 	"net"
 	"net/http"
 	"time"
@@ -30,6 +32,29 @@ import (
 	"k8s.io/apiserver/pkg/storage/storagebackend"
 )
 
+func newETCD2HealthCheck(c storagebackend.Config) (func() error, error) {
+	tr, err := newTransportForETCD2(c.CertFile, c.KeyFile, c.CAFile)
+	if err != nil {
+		return nil, err
+	}
+
+	client, err := newETCD2Client(tr, c.ServerList)
+	if err != nil {
+		return nil, err
+	}
+
+	members := etcd2client.NewMembersAPI(client)
+
+	return func() error {
+		ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+		defer cancel()
+		if _, err := members.List(ctx); err != nil {
+			return fmt.Errorf("error listing etcd members: %v", err)
+		}
+		return nil
+	}, nil
+}
+
 func newETCD2Storage(c storagebackend.Config) (storage.Interface, DestroyFunc, error) {
 	tr, err := newTransportForETCD2(c.CertFile, c.KeyFile, c.CAFile)
 	if err != nil {

staging/src/k8s.io/apiserver/pkg/storage/storagebackend/factory/etcd3.go

@@ -18,11 +18,14 @@ package factory
 
 import (
 	"context"
+	"fmt"
+	"sync/atomic"
 	"time"
 
 	"github.com/coreos/etcd/clientv3"
 	"github.com/coreos/etcd/pkg/transport"
 
+	"k8s.io/apimachinery/pkg/util/wait"
 	"k8s.io/apiserver/pkg/storage"
 	"k8s.io/apiserver/pkg/storage/etcd3"
 	"k8s.io/apiserver/pkg/storage/storagebackend"
@@ -38,15 +41,49 @@ var (
 	dialTimeout = 10 * time.Second
 )
 
-func newETCD3Storage(c storagebackend.Config) (storage.Interface, DestroyFunc, error) {
+func newETCD3HealthCheck(c storagebackend.Config) (func() error, error) {
+	// constructing the etcd v3 client blocks and times out if etcd is not available.
+	// retry in a loop in the background until we successfully create the client, storing the client or error encountered
+
+	clientValue := &atomic.Value{}
+
+	clientErrMsg := &atomic.Value{}
+	clientErrMsg.Store("etcd client connection not yet established")
+
+	go wait.PollUntil(time.Second, func() (bool, error) {
+		client, err := newETCD3Client(c)
+		if err != nil {
+			clientErrMsg.Store(err.Error())
+			return false, nil
+		}
+		clientValue.Store(client)
+		clientErrMsg.Store("")
+		return true, nil
+	}, wait.NeverStop)
+
+	return func() error {
+		if errMsg := clientErrMsg.Load().(string); len(errMsg) > 0 {
+			return fmt.Errorf(errMsg)
+		}
+		client := clientValue.Load().(*clientv3.Client)
+		ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+		defer cancel()
+		if _, err := client.Cluster.MemberList(ctx); err != nil {
+			return fmt.Errorf("error listing etcd members: %v", err)
+		}
+		return nil
+	}, nil
+}
+
+func newETCD3Client(c storagebackend.Config) (*clientv3.Client, error) {
 	tlsInfo := transport.TLSInfo{
 		CertFile: c.CertFile,
 		KeyFile:  c.KeyFile,
 		CAFile:   c.CAFile,
 	}
 	tlsConfig, err := tlsInfo.ClientConfig()
 	if err != nil {
-		return nil, nil, err
+		return nil, err
 	}
 	// NOTE: Client relies on nil tlsConfig
 	// for non-secure connections, update the implicit variable
@@ -61,6 +98,11 @@ func newETCD3Storage(c storagebackend.Config) (storage.Interface, DestroyFunc, e
 		TLS:                  tlsConfig,
 	}
 	client, err := clientv3.New(cfg)
+	return client, err
+}
+
+func newETCD3Storage(c storagebackend.Config) (storage.Interface, DestroyFunc, error) {
+	client, err := newETCD3Client(c)
 	if err != nil {
 		return nil, nil, err
 	}

staging/src/k8s.io/apiserver/pkg/storage/storagebackend/factory/factory.go

@@ -41,3 +41,15 @@ func Create(c storagebackend.Config) (storage.Interface, DestroyFunc, error) {
 		return nil, nil, fmt.Errorf("unknown storage type: %s", c.Type)
 	}
 }
+
+// CreateHealthCheck creates a healthcheck function based on given config.
+func CreateHealthCheck(c storagebackend.Config) (func() error, error) {
+	switch c.Type {
+	case storagebackend.StorageTypeETCD2:
+		return newETCD2HealthCheck(c)
+	case storagebackend.StorageTypeUnset, storagebackend.StorageTypeETCD3:
+		return newETCD3HealthCheck(c)
+	default:
+		return nil, fmt.Errorf("unknown storage type: %s", c.Type)
+	}
+}