Added more comments.

cluster/saltbase/salt/kube-master-addons/init.sls

@@ -39,10 +39,17 @@ master-docker-image-tags:
 
 # Current containervm image by default has both docker and kubelet
 # running. But during cluster creation stage, docker and kubelet
-# could be overwritten completely, or restarted due flag changes.
+# could be overwritten completely, or restarted due to flag changes.
 # The ordering of salt states for service docker, kubelet and
 # master-addon below is very important to avoid the race between
 # salt restart docker or kubelet and kubelet start master components.
+# Without the ordering of salt states, when gce instance boot up,
+# configure-vm.sh will run and download the release. At the end of
+# boot, run-salt will run kube-master-addons service which installs
+# master component manifest files to kubelet config directory before
+# the installation of proper version kubelet. Please see
+# https://github.com/GoogleCloudPlatform/kubernetes/issues/10122#issuecomment-114566063
+# for detail explanation on this very issue.
 kube-master-addons:
   service.running:
     - enable: True

pkg/kubelet/container_bridge.go

@@ -85,6 +85,9 @@ func ensureCbr0(wantCIDR *net.IPNet) error {
 	return nil
 }
 
+// Check if cbr0 network interface is configured or not, and take action
+// when the configuration is missing on the node, and propagate the rest
+// error to kubelet to handle.
 func cbr0Exists() (bool, error) {
 	if _, err := os.Stat("/sys/class/net/cbr0"); err != nil {
 		if os.IsNotExist(err) {