Exit NGF container when leader lease is lost (#1130)

Problem: If NGF Pod loses connection to the API server and cannot renew the leader election lease, it stops leading and cannot become the leader again. After it stops leading, it will not report any statuses until it is restarted.

Solution: Update the leader elector Start method to return an error if the leader lease is lost. This will cause the controller-runtime manager to exit, and the NGF container will restart. The new container will then attempt to become the leader again. This aligns with how the controller-runtime library handles losing a leader lease.

internal/mode/static/leader.go

@@ -2,6 +2,7 @@ package static
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"time"
 
@@ -43,10 +44,21 @@ type leaderElectorRunnable struct {
 	le *leaderelection.LeaderElector
 }
 
-// Start runs the leaderelection.LeaderElector and blocks until the context is canceled or Run returns.
+// Start runs the leaderelection.LeaderElector and blocks until the context is canceled or the leader lease is lost.
+// If the leader lease is lost, Start returns an error, and the controller-runtime manager will exit, causing the Pod
+// to restart. This is necessary otherwise components that need leader election might continue to run after the leader
+// lease was lost.
 func (l *leaderElectorRunnable) Start(ctx context.Context) error {
 	l.le.Run(ctx)
-	return nil
+
+	// Run exits if the context is canceled or the leader lease is lost. We only want to return an error if the
+	// context is not canceled.
+	select {
+	case <-ctx.Done():
+		return nil
+	default:
+		return errors.New("leader election lost")
+	}
 }
 
 // IsLeader returns if the Pod is the current leader.