Merge pull request #28034 from krousey/kubeconfig_filelock

Automatic merge from submit-queue

Adding lock files for kubeconfig updating

This is to prevent concurrent executions from corrupting the kubeconfig file. 

Also, release note?

#23964

pkg/client/unversioned/clientcmd/loader.go

@@ -381,12 +381,38 @@ func WriteToFile(config clientcmdapi.Config, filename string) error {
 			return err
 		}
 	}
+
+	err = lockFile(filename)
+	if err != nil {
+		return err
+	}
+	defer unlockFile(filename)
+
 	if err := ioutil.WriteFile(filename, content, 0600); err != nil {
 		return err
 	}
 	return nil
 }
 
+func lockFile(filename string) error {
+	// TODO: find a way to do this with actual file locks. Will
+	// probably need seperate solution for windows and linux.
+	f, err := os.OpenFile(lockName(filename), os.O_CREATE|os.O_EXCL, 0)
+	if err != nil {
+		return err
+	}
+	f.Close()
+	return nil
+}
+
+func unlockFile(filename string) error {
+	return os.Remove(lockName(filename))
+}
+
+func lockName(filename string) string {
+	return filename + ".lock"
+}
+
 // Write serializes the config to yaml.
 // Encapsulates serialization without assuming the destination is a file.
 func Write(config clientcmdapi.Config) ([]byte, error) {

pkg/client/unversioned/clientcmd/loader_test.go

@@ -376,6 +376,22 @@ func TestMigratingFileSourceMissingSkip(t *testing.T) {
 	}
 }
 
+func TestFileLocking(t *testing.T) {
+	f, _ := ioutil.TempFile("", "")
+	defer os.Remove(f.Name())
+
+	err := lockFile(f.Name())
+	if err != nil {
+		t.Errorf("unexpected error while locking file: %v", err)
+	}
+	defer unlockFile(f.Name())
+
+	err = lockFile(f.Name())
+	if err == nil {
+		t.Error("expected error while locking file.")
+	}
+}
+
 func Example_noMergingOnExplicitPaths() {
 	commandLineFile, _ := ioutil.TempFile("", "")
 	defer os.Remove(commandLineFile.Name())