etcd: use Unix Domain socket for testserver

Choosing a port in advance is racy. A better solution is to use a Unix Domain
socket in the per-etcd-instance data directory. Then the name can be determined
in advance and there's no risk of conflicts with other etcd instances.

With unix:// for the endpoint, we have to be a bit more careful about
passing a TLS config to the etcd client library because for unix://, in
contrast to http://, it tries to use an incomplete config which
then fails to establish the connection.

cmd/kube-apiserver/app/testing/testserver.go

@@ -22,6 +22,7 @@ import (
 	"crypto/elliptic"
 	"crypto/rand"
 	"crypto/rsa"
+	"crypto/tls"
 	"crypto/x509"
 	"crypto/x509/pkix"
 	"encoding/pem"
@@ -501,26 +502,9 @@ func StartTestServer(t ktesting.TB, instanceOptions *TestServerInstanceOptions,
 		return result, fmt.Errorf("failed to wait for default namespace to be created: %v", err)
 	}
 
-	tlsInfo := transport.TLSInfo{
-		CertFile:      storageConfig.Transport.CertFile,
-		KeyFile:       storageConfig.Transport.KeyFile,
-		TrustedCAFile: storageConfig.Transport.TrustedCAFile,
-	}
-	tlsConfig, err := tlsInfo.ClientConfig()
+	etcdClient, _, err := GetEtcdClients(storageConfig.Transport)
 	if err != nil {
-		return result, err
-	}
-	etcdConfig := clientv3.Config{
-		Endpoints:   storageConfig.Transport.ServerList,
-		DialTimeout: 20 * time.Second,
-		DialOptions: []grpc.DialOption{
-			grpc.WithBlock(), // block until the underlying connection is up
-		},
-		TLS: tlsConfig,
-	}
-	etcdClient, err := clientv3.New(etcdConfig)
-	if err != nil {
-		return result, err
+		return result, fmt.Errorf("create etcd client: %w", err)
 	}
 
 	// from here the caller must call tearDown
@@ -538,6 +522,45 @@ func StartTestServer(t ktesting.TB, instanceOptions *TestServerInstanceOptions,
 	return result, nil
 }
 
+// GetEtcdClients returns an initialized etcd clientv3.Client and clientv3.KV.
+func GetEtcdClients(config storagebackend.TransportConfig) (*clientv3.Client, clientv3.KV, error) {
+	// clientv3.New ignores an invalid TLS config for http://, but not for unix:// (https://github.com/etcd-io/etcd/blob/5a8fba466087686fc15815f5bc041fb7eb1f23ea/client/v3/internal/endpoint/endpoint.go#L61-L66).
+	// To support unix://, we must not set Config.TLS unless we really have
+	// transport security.
+	var tlsConfig *tls.Config
+	if config.CertFile != "" ||
+		config.KeyFile != "" ||
+		config.TrustedCAFile != "" {
+		tlsInfo := transport.TLSInfo{
+			CertFile:      config.CertFile,
+			KeyFile:       config.KeyFile,
+			TrustedCAFile: config.TrustedCAFile,
+		}
+
+		var err error
+		tlsConfig, err = tlsInfo.ClientConfig()
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+
+	cfg := clientv3.Config{
+		Endpoints:   config.ServerList,
+		DialTimeout: 20 * time.Second,
+		DialOptions: []grpc.DialOption{
+			grpc.WithBlock(), // block until the underlying connection is up
+		},
+		TLS: tlsConfig,
+	}
+
+	c, err := clientv3.New(cfg)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return c, clientv3.NewKV(c), nil
+}
+
 // StartTestServerOrDie calls StartTestServer t.Fatal if it does not succeed.
 func StartTestServerOrDie(t testing.TB, instanceOptions *TestServerInstanceOptions, flags []string, storageConfig *storagebackend.Config) *TestServer {
 	result, err := StartTestServer(t, instanceOptions, flags, storageConfig)

test/integration/framework/controlplane_utils.go

@@ -86,6 +86,12 @@ func DefaultEtcdOptions() *options.EtcdOptions {
 }
 
 // SharedEtcd creates a storage config for a shared etcd instance, with a unique prefix.
+//
+// The transport CertFile/KeyFile/TrustedCAFile will be empty for insecure connections.
+// In that case, *no* TLS config should be used because etcd would try to use
+// it for Unix Domain sockets (https://github.com/etcd-io/etcd/blob/5a8fba466087686fc15815f5bc041fb7eb1f23ea/client/v3/internal/endpoint/endpoint.go#L61-L66)
+// and fail to connect because the TLS config is insufficient. It works
+// for TCP because http disables using TLS.
 func SharedEtcd() *storagebackend.Config {
 	cfg := storagebackend.NewDefaultConfig(path.Join(uuid.New().String(), "registry"), nil)
 	cfg.Transport.ServerList = []string{GetEtcdURL()}

test/integration/framework/etcd.go

@@ -24,6 +24,7 @@ import (
 	"net"
 	"os"
 	"os/exec"
+	"path"
 	"strconv"
 	"strings"
 	"sync"
@@ -51,18 +52,6 @@ func getEtcdPath() (string, error) {
 	return exec.LookPath("etcd")
 }
 
-// getAvailablePort returns a TCP port that is available for binding.
-func getAvailablePort() (int, error) {
-	l, err := net.Listen("tcp", ":0")
-	if err != nil {
-		return 0, fmt.Errorf("could not bind to a port: %v", err)
-	}
-	// It is possible but unlikely that someone else will bind this port before we
-	// get a chance to use it.
-	defer l.Close()
-	return l.Addr().(*net.TCPAddr).Port, nil
-}
-
 // startEtcd executes an etcd instance. The returned function will signal the
 // etcd process and wait for it to exit.
 func startEtcd(output io.Writer, forceCreate bool) (func(), error) {
@@ -105,28 +94,30 @@ func RunCustomEtcd(dataDir string, customFlags []string, output io.Writer) (url
 		fmt.Fprint(os.Stderr, installEtcd)
 		return "", nil, fmt.Errorf("could not find etcd in PATH: %v", err)
 	}
-	etcdPort, err := getAvailablePort()
-	if err != nil {
-		return "", nil, fmt.Errorf("could not get a port: %v", err)
-	}
-	customURL := fmt.Sprintf("http://127.0.0.1:%d", etcdPort)
-
-	klog.Infof("starting etcd on %s", customURL)
-
 	etcdDataDir, err := os.MkdirTemp(os.TempDir(), dataDir)
 	if err != nil {
 		return "", nil, fmt.Errorf("unable to make temp etcd data dir %s: %v", dataDir, err)
 	}
-	klog.Infof("storing etcd data in: %v", etcdDataDir)
+	etcdSocketPath := path.Join(etcdDataDir, "etcd.sock")
+	customURL := "unix://" + etcdSocketPath
 
+	klog.V(2).InfoS("starting etcd", "url", customURL, "dataDir", etcdDataDir)
 	ctx, cancel := context.WithCancel(context.Background())
 	args := []string{
 		"--data-dir",
 		etcdDataDir,
 		"--listen-client-urls",
 		customURL,
+		// This should be how clients connect to etcd, but https://github.com/etcd-io/etcd/pull/12469
+		// apparently was incomplete: trying to pass a Unix Domain URL here is rejected by ectd 3.15.13 with
+		//    --advertise-client-urls "unix:///tmp/etcd.sock" must be "host:port" (missing port in address)
+		//
+		// We don't need to advertise the correct address. To prevent connecting to the default URL
+		// in the unlikely case that something does use this URL after all, an invalid URL is set here.
 		"--advertise-client-urls",
-		customURL,
+		"http://127.0.0.111:0",
+		// With :0 we let the kernel pick a unique port. We don't care which port this will be,
+		// no other peer is going to connect.
 		"--listen-peer-urls",
 		"http://127.0.0.1:0",
 		"-log-level",
@@ -176,7 +167,7 @@ func RunCustomEtcd(dataDir string, customFlags []string, output io.Writer) (url
 	const pollCount = int32(300)
 
 	for i <= pollCount {
-		conn, err := net.DialTimeout("tcp", strings.TrimPrefix(customURL, "http://"), 1*time.Second)
+		conn, err := net.DialTimeout("unix", etcdSocketPath, 1*time.Second)
 		if err == nil {
 			conn.Close()
 			break

test/integration/utils.go

@@ -21,16 +21,15 @@ import (
 	"testing"
 	"time"
 
-	"google.golang.org/grpc"
+	clientv3 "go.etcd.io/etcd/client/v3"
+
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/util/wait"
 	"k8s.io/apiserver/pkg/storage/storagebackend"
 	clientset "k8s.io/client-go/kubernetes"
 	coreclient "k8s.io/client-go/kubernetes/typed/core/v1"
-
-	"go.etcd.io/etcd/client/pkg/v3/transport"
-	clientv3 "go.etcd.io/etcd/client/v3"
+	kubeapiservertesting "k8s.io/kubernetes/cmd/kube-apiserver/app/testing"
 )
 
 // DeletePodOrErrorf deletes a pod or fails with a call to t.Errorf.
@@ -67,32 +66,7 @@ func WaitForPodToDisappear(podClient coreclient.PodInterface, podName string, in
 	})
 }
 
-// GetEtcdClients returns an initialized  clientv3.Client and clientv3.KV.
+// GetEtcdClients returns an initialized etcd clientv3.Client and clientv3.KV.
 func GetEtcdClients(config storagebackend.TransportConfig) (*clientv3.Client, clientv3.KV, error) {
-	tlsInfo := transport.TLSInfo{
-		CertFile:      config.CertFile,
-		KeyFile:       config.KeyFile,
-		TrustedCAFile: config.TrustedCAFile,
-	}
-
-	tlsConfig, err := tlsInfo.ClientConfig()
-	if err != nil {
-		return nil, nil, err
-	}
-
-	cfg := clientv3.Config{
-		Endpoints:   config.ServerList,
-		DialTimeout: 20 * time.Second,
-		DialOptions: []grpc.DialOption{
-			grpc.WithBlock(), // block until the underlying connection is up
-		},
-		TLS: tlsConfig,
-	}
-
-	c, err := clientv3.New(cfg)
-	if err != nil {
-		return nil, nil, err
-	}
-
-	return c, clientv3.NewKV(c), nil
+	return kubeapiservertesting.GetEtcdClients(config)
 }