add leader election support for external snapshotter

Signed-off-by: Andrew Sy Kim <kiman@vmware.com>

cmd/csi-snapshotter/main.go

@@ -34,6 +34,7 @@ import (
 
 	"github.com/container-storage-interface/spec/lib/go/csi"
 	"github.com/kubernetes-csi/csi-lib-utils/connection"
+	"github.com/kubernetes-csi/csi-lib-utils/leaderelection"
 	csirpc "github.com/kubernetes-csi/csi-lib-utils/rpc"
 	"github.com/kubernetes-csi/external-snapshotter/pkg/controller"
 	"github.com/kubernetes-csi/external-snapshotter/pkg/snapshotter"
@@ -65,10 +66,14 @@ var (
 	snapshotNamePrefix              = flag.String("snapshot-name-prefix", "snapshot", "Prefix to apply to the name of a created snapshot")
 	snapshotNameUUIDLength          = flag.Int("snapshot-name-uuid-length", -1, "Length in characters for the generated uuid of a created snapshot. Defaults behavior is to NOT truncate.")
 	showVersion                     = flag.Bool("version", false, "Show version.")
+
+	leaderElection          = flag.Bool("leader-election", false, "Enables leader election.")
+	leaderElectionNamespace = flag.String("leader-election-namespace", "", "The namespace where the leader election resource exists. Defaults to the pod namespace if not set.")
 )
 
 var (
 	version                = "unknown"
+	leaderElectionLockName = "external-snapshotter-leader-election"
 )
 
 func main() {
@@ -192,6 +197,7 @@ func main() {
 		*snapshotNameUUIDLength,
 	)
 
+	run := func(context.Context) {
 		// run...
 		stopCh := make(chan struct{})
 		factory.Start(stopCh)
@@ -205,6 +211,19 @@ func main() {
 		close(stopCh)
 	}
 
+	if !*leaderElection {
+		run(context.TODO())
+	} else {
+		le := leaderelection.NewLeaderElection(kubeClient, leaderElectionLockName, run)
+		if *leaderElectionNamespace != "" {
+			le.WithNamespace(*leaderElectionNamespace)
+		}
+		if err := le.Run(); err != nil {
+			klog.Fatalf("failed to initialize leader election: %v", err)
+		}
+	}
+}
+
 func buildConfig(kubeconfig string) (*rest.Config, error) {
 	if kubeconfig != "" {
 		return clientcmd.BuildConfigFromFlags("", kubeconfig)