Merge pull request #60654 from dcbw/kubelet-notify-systemd

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

kubelet: notify systemd that kubelet has started

This call has no side-effects if systemd is not used or not installed.

Fixes: https://github.com/kubernetes/kubernetes/issues/59079

@smarterclayton @sjenning 

```release-note
kubelet now notifies systemd that it has finished starting, if systemd is available and running.
```

cmd/kubelet/app/BUILD

@@ -131,6 +131,7 @@ go_library(
         "//pkg/volume/secret:go_default_library",
         "//pkg/volume/storageos:go_default_library",
         "//pkg/volume/vsphere_volume:go_default_library",
+        "//vendor/github.com/coreos/go-systemd/daemon:go_default_library",
         "//vendor/github.com/golang/glog:go_default_library",
         "//vendor/github.com/spf13/cobra:go_default_library",
         "//vendor/github.com/spf13/pflag:go_default_library",

cmd/kubelet/app/server.go

@@ -31,8 +31,10 @@ import (
 	"path"
 	"path/filepath"
 	"strconv"
+	"sync"
 	"time"
 
+	"github.com/coreos/go-systemd/daemon"
 	"github.com/golang/glog"
 	"github.com/spf13/cobra"
 	"github.com/spf13/pflag"
@@ -697,6 +699,9 @@ func run(s *options.KubeletServer, kubeDeps *kubelet.Dependencies) (err error) {
 		return nil
 	}
 
+	// If systemd is used, notify it that we have started
+	go daemon.SdNotify(false, "READY=1")
+
 	<-done
 	return nil
 }
@@ -937,20 +942,31 @@ func RunKubelet(kubeFlags *options.KubeletFlags, kubeCfg *kubeletconfiginternal.
 }
 
 func startKubelet(k kubelet.Bootstrap, podCfg *config.PodConfig, kubeCfg *kubeletconfiginternal.KubeletConfiguration, kubeDeps *kubelet.Dependencies, enableServer bool) {
+	wg := sync.WaitGroup{}
+
 	// start the kubelet
-	go wait.Until(func() { k.Run(podCfg.Updates()) }, 0, wait.NeverStop)
+	wg.Add(1)
+	go wait.Until(func() {
+		wg.Done()
+		k.Run(podCfg.Updates())
+	}, 0, wait.NeverStop)
 
 	// start the kubelet server
 	if enableServer {
+		wg.Add(1)
 		go wait.Until(func() {
+			wg.Done()
 			k.ListenAndServe(net.ParseIP(kubeCfg.Address), uint(kubeCfg.Port), kubeDeps.TLSOptions, kubeDeps.Auth, kubeCfg.EnableDebuggingHandlers, kubeCfg.EnableContentionProfiling)
 		}, 0, wait.NeverStop)
 	}
 	if kubeCfg.ReadOnlyPort > 0 {
+		wg.Add(1)
 		go wait.Until(func() {
+			wg.Done()
 			k.ListenAndServeReadOnly(net.ParseIP(kubeCfg.Address), uint(kubeCfg.ReadOnlyPort))
 		}, 0, wait.NeverStop)
 	}
+	wg.Wait()
 }
 
 func CreateAndInitKubelet(kubeCfg *kubeletconfiginternal.KubeletConfiguration,