DHCP lease maintenance should terminate when interface no longer exists.

Due to oberservations that threads can grow and the dhcp daemon uses an increasing amount of memory.

This situation can happen organically when using say, bridge CNI, and the bridge has been removed outside of the bridge CNI lifecycle, and an interface no longer exists on a pod.

Does so on a retry loop using the `backoffRetry()` method.

Signed-off-by: dougbtv <dosmith@redhat.com>

Author: dougbtv

plugins/ipam/dhcp/lease.go

@@ -55,6 +55,12 @@ const (
 	leaseStateRebinding
 )
 
+// Timing for retrying link existence check
+const (
+    linkCheckRetryMax      = 10 * time.Second
+    linkCheckTotalTimeout = 30 * time.Second
+)
+
 // This implementation uses 1 OS thread per lease. This is because
 // all the network operations have to be done in network namespace
 // of the interface. This can be improved by switching to the proper
@@ -292,6 +298,14 @@ func (l *DHCPLease) maintain() {
 	for {
 		var sleepDur time.Duration
 
+		linkCheckCtx, cancel := context.WithTimeoutCause(l.ctx, l.resendTimeout, errNoMoreTries)
+		defer cancel()
+		err := l.checkLinkExistsWithBackoff(linkCheckCtx)
+		if err != nil {
+			log.Printf("%v: interface %s no longer exists or check failed, terminating lease maintenance (last encountered: %v)", l.clientID, l.link.Attrs().Name, err)
+			return
+		}
+
 		switch state {
 		case leaseStateBound:
 			sleepDur = time.Until(l.renewalTime)
@@ -344,6 +358,23 @@ func (l *DHCPLease) maintain() {
 	}
 }
 
+// checkLinkExistsWithBackoff uses backoffRetry to check if a network link exists
+func (l *DHCPLease) checkLinkExistsWithBackoff(ctx context.Context) error {
+    checkFunc := func() (*nclient4.Lease, error) {
+		// Returns the error to trigger a retry.
+        if _, err := netlink.LinkByName(l.link.Attrs().Name); err != nil {
+            return nil, err
+        }
+        return nil, nil
+    }
+
+    ctx, cancel := context.WithTimeout(ctx, linkCheckTotalTimeout)
+    defer cancel()
+    _, err := backoffRetry(ctx, linkCheckRetryMax, checkFunc)
+    return err
+}
+
+
 func (l *DHCPLease) downIface() {
 	if err := netlink.LinkSetDown(l.link); err != nil {
 		log.Printf("%v: failed to bring %v interface DOWN: %v", l.clientID, l.link.Attrs().Name, err)