reload cni network config if has fs change events

With go RWMutex design, no goroutine should expect to be able to
acquire a read lock until the read lock has been released, if one
goroutine call lock.

The original design is to reload cni network config on every single
Status CRI gRPC call. If one RunPodSandbox request holds read lock
to allocate IP for too long, all other RunPodSandbox/StopPodSandbox
requests will wait for the RunPodSandbox request to release read lock.
And the Status CRI call will fail and kubelet becomes NOTReady.

Reload cni network config at every single Status CRI call is not
necessary and also brings NOTReady situation. To lower the possibility
of NOTReady, CRI will reload cni network config if there is any valid fs
change events from the cni network config dir.

Signed-off-by: Wei Fu <fuweid89@gmail.com>

pkg/server/service.go

@@ -91,6 +91,9 @@ type criService struct {
 	// initialized indicates whether the server is initialized. All GRPC services
 	// should return error before the server is initialized.
 	initialized atomic.Bool
+	// cniNetConfMonitor is used to reload cni network conf if there is
+	// any valid fs change events from cni network conf dir.
+	cniNetConfMonitor *cniNetConfSyncer
 }
 
 // NewCRIService returns a new instance of CRIService
@@ -128,6 +131,11 @@ func NewCRIService(config criconfig.Config, client *containerd.Client) (CRIServi
 
 	c.eventMonitor = newEventMonitor(c)
 
+	c.cniNetConfMonitor, err = newCNINetConfSyncer(c.config.NetworkPluginConfDir, c.netPlugin, c.cniLoadOptions())
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to create cni conf monitor")
+	}
+
 	return c, nil
 }
 
@@ -169,6 +177,14 @@ func (c *criService) Run() error {
 	)
 	snapshotsSyncer.start()
 
+	// Start CNI network conf syncer
+	logrus.Info("Start cni network conf syncer")
+	cniNetConfMonitorErrCh := make(chan error, 1)
+	go func() {
+		defer close(cniNetConfMonitorErrCh)
+		cniNetConfMonitorErrCh <- c.cniNetConfMonitor.syncLoop()
+	}()
+
 	// Start streaming server.
 	logrus.Info("Start streaming server")
 	streamServerErrCh := make(chan error)
@@ -183,11 +199,12 @@ func (c *criService) Run() error {
 	// Set the server as initialized. GRPC services could start serving traffic.
 	c.initialized.Set()
 
-	var eventMonitorErr, streamServerErr error
+	var eventMonitorErr, streamServerErr, cniNetConfMonitorErr error
 	// Stop the whole CRI service if any of the critical service exits.
 	select {
 	case eventMonitorErr = <-eventMonitorErrCh:
 	case streamServerErr = <-streamServerErrCh:
+	case cniNetConfMonitorErr = <-cniNetConfMonitorErrCh:
 	}
 	if err := c.Close(); err != nil {
 		return errors.Wrap(err, "failed to stop cri service")
@@ -222,6 +239,9 @@ func (c *criService) Run() error {
 	if streamServerErr != nil {
 		return errors.Wrap(streamServerErr, "stream server error")
 	}
+	if cniNetConfMonitorErr != nil {
+		return errors.Wrap(cniNetConfMonitorErr, "cni network conf monitor error")
+	}
 	return nil
 }
 
@@ -229,6 +249,9 @@ func (c *criService) Run() error {
 // TODO(random-liu): Make close synchronous.
 func (c *criService) Close() error {
 	logrus.Info("Stop CRI service")
+	if err := c.cniNetConfMonitor.stop(); err != nil {
+		logrus.WithError(err).Error("failed to stop cni network conf monitor")
+	}
 	c.eventMonitor.stop()
 	if err := c.streamServer.Stop(); err != nil {
 		return errors.Wrap(err, "failed to stop stream server")