kubelet: Add --exit-on-lock-contention flag

This patch adds the --exit-on-lock-contention flag, which must be used
in conjunction with the --lock-file flag. When provided, it causes the
kubelet to wait for inotify events for that lock file. When an 'open'
event is received, the kubelet will exit.

cmd/kubelet/app/server.go

@@ -19,6 +19,7 @@ package app
 
 import (
 	"crypto/tls"
+	"errors"
 	"fmt"
 	"math/rand"
 	"net"
@@ -289,11 +290,22 @@ func Run(s *options.KubeletServer, kcfg *KubeletConfig) error {
 }
 
 func run(s *options.KubeletServer, kcfg *KubeletConfig) (err error) {
+	if s.ExitOnLockContention && s.LockFilePath == "" {
+		return errors.New("cannot exit on lock file contention: no lock file specified")
+	}
+
+	done := make(chan struct{})
 	if s.LockFilePath != "" {
 		glog.Infof("aquiring lock on %q", s.LockFilePath)
 		if err := flock.Acquire(s.LockFilePath); err != nil {
 			return fmt.Errorf("unable to aquire file lock on %q: %v", s.LockFilePath, err)
 		}
+		if s.ExitOnLockContention {
+			glog.Infof("watching for inotify events for: %v", s.LockFilePath)
+			if err := watchForLockfileContention(s.LockFilePath, done); err != nil {
+				return err
+			}
+		}
 	}
 	if c, err := configz.New("componentconfig"); err == nil {
 		c.Set(s.KubeletConfiguration)
@@ -383,8 +395,8 @@ func run(s *options.KubeletServer, kcfg *KubeletConfig) (err error) {
 		return nil
 	}
 
-	// run forever
-	select {}
+	<-done
+	return nil
 }
 
 // InitializeTLS checks for a configured TLSCertFile and TLSPrivateKeyFile: if unspecified a new self-signed