Bug 1864352: Add leader election mechanism to release-4.5

This cherry-picks the fix from master/4.6 and integrates with:
openshift/machine-api-operator#664

Adding 3 new cli arguments for configuring leader elections:
-leader-elect
-leader-elect-lease-duration int
-leader-elect-resource-namespace string

Using leader election will add stronger guarantees than we have today
that only one controller is running at a time to protect against edge
cases where the deployment replica could be increased or upgrades with
permissive maxSurge.

(cherry picked from commit 5ccc992)

cmd/manager/main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"flag"
+	"time"
 
 	"github.com/golang/glog"
 	"github.com/openshift/cluster-api-provider-libvirt/pkg/apis"
@@ -25,6 +26,25 @@ func main() {
 	watchNamespace := flag.String("namespace", "", "Namespace that the controller watches to reconcile machine-api objects. If unspecified, the controller watches for machine-api objects across all namespaces.")
 	klogFlags := flag.NewFlagSet("klog", flag.ExitOnError)
 	klog.InitFlags(klogFlags)
+
+	leaderElectResourceNamespace := flag.String(
+		"leader-elect-resource-namespace",
+		"",
+		"The namespace of resource object that is used for locking during leader election. If unspecified and running in cluster, defaults to the service account namespace for the controller. Required for leader-election outside of a cluster.",
+	)
+
+	leaderElect := flag.Bool(
+		"leader-elect",
+		false,
+		"Start a leader election client and gain leadership before executing the main loop. Enable this when running replicated components for high availability.",
+	)
+
+	leaderElectLeaseDuration := flag.Duration(
+		"leader-elect-lease-duration",
+		15*time.Second,
+		"The duration that non-leader candidates will wait after observing a leadership renewal until attempting to acquire leadership of a led but unrenewed leader slot. This is effectively the maximum duration that a leader can be stopped before it is replaced by another candidate. This is only applicable if leader election is enabled.",
+	)
+
 	flag.Parse()
 	flag.VisitAll(func(f1 *flag.Flag) {
 		f2 := klogFlags.Lookup(f1.Name)
@@ -40,7 +60,12 @@ func main() {
 		glog.Fatal(err)
 	}
 
-	opts := manager.Options{}
+	opts := manager.Options{
+		LeaderElection:          *leaderElect,
+		LeaderElectionNamespace: *leaderElectResourceNamespace,
+		LeaderElectionID:        "cluster-api-provider-libvirt-leader",
+		LeaseDuration:           leaderElectLeaseDuration,
+	}
 
 	if *watchNamespace != "" {
 		opts.Namespace = *watchNamespace