fix: add nil checks to prevent panics in leaderelection

- Add nil checks for callback functions (OnStartedLeading/OnStoppedLeading)
- Add nil checks for lease pointer in isHolderOf method
- Add nil checks for observedLease and LeaseDurationSeconds in isLeaseValid method
- Prevents runtime panics when callbacks are not provided or lease fields are nil

This change improves robustness by adding defensive nil checks throughout
the leaderelection code, particularly for callback functions that may not
always be provided and for lease object fields that could be nil.

Author: haitwang-cloud

pkg/util/leaderelection/leaderelection.go

@@ -116,7 +116,7 @@ func (m *leaderManager) onAdd(obj any) {
 
 	m.setObservedRecord(lease)
 	// Notify if we are the leader from the very begging
-	if m.isHolderOf(lease) {
+	if m.isHolderOf(lease) && m.callbacks.OnStartedLeading != nil {
 		m.callbacks.OnStartedLeading()
 	}
 }
@@ -138,9 +138,13 @@ func (m *leaderManager) onUpdate(oldObj, newObj any) {
 
 	// Notify if we have been elected to become the leader
 	if !m.isHolderOf(oldLease) && m.isHolderOf(newLease) {
-		m.callbacks.OnStartedLeading()
+		if m.callbacks.OnStartedLeading != nil {
+			m.callbacks.OnStartedLeading()
+		}
 	} else if m.isHolderOf(oldLease) && !m.isHolderOf(newLease) {
-		m.callbacks.OnStoppedLeading()
+		if m.callbacks.OnStoppedLeading != nil {
+			m.callbacks.OnStoppedLeading()
+		}
 	}
 }
 
@@ -150,15 +154,23 @@ func (m *leaderManager) onDelete(obj any) {
 	defer m.leaseLock.Unlock()
 
 	m.setObservedRecord(nil)
-	m.callbacks.OnStoppedLeading()
+	if m.callbacks.OnStoppedLeading != nil {
+		m.callbacks.OnStoppedLeading()
+	}
 }
 
 func (m *leaderManager) isHolderOf(lease *coordinationv1.Lease) bool {
 	// kube-scheduler lease id take format of `hostname + "_" + string(uuid.NewUUID())`
-	return lease.Spec.HolderIdentity != nil && strings.HasPrefix(*lease.Spec.HolderIdentity, m.hostname)
+	if lease == nil || lease.Spec.HolderIdentity == nil {
+		return false
+	}
+	return strings.HasPrefix(*lease.Spec.HolderIdentity, m.hostname)
 }
 
 func (m *leaderManager) isLeaseValid(now time.Time) bool {
+	if m.observedLease == nil || m.observedLease.Spec.LeaseDurationSeconds == nil {
+		return false
+	}
 	return m.observedTime.Add(time.Second * time.Duration(*m.observedLease.Spec.LeaseDurationSeconds)).After(now)
 }