Allow configuring the rkt binary in a kubelet with a flag.

This is necessary because coreos comes with rkt installed, and if we want to use a different version
we need some way to avoid the default one.

cmd/kubelet/app/server.go

@@ -116,6 +116,7 @@ type KubeletServer struct {
 	ResourceContainer              string
 	CgroupRoot                     string
 	ContainerRuntime               string
+	RktPath                        string
 	DockerDaemonContainer          string
 	SystemContainer                string
 	ConfigureCBR0                  bool
@@ -182,6 +183,7 @@ func NewKubeletServer() *KubeletServer {
 		ResourceContainer:           "/kubelet",
 		CgroupRoot:                  "",
 		ContainerRuntime:            "docker",
+		RktPath:                     "",
 		DockerDaemonContainer:       "/docker-daemon",
 		SystemContainer:             "",
 		ConfigureCBR0:               false,
@@ -245,6 +247,7 @@ func (s *KubeletServer) AddFlags(fs *pflag.FlagSet) {
 	fs.StringVar(&s.ResourceContainer, "resource-container", s.ResourceContainer, "Absolute name of the resource-only container to create and run the Kubelet in (Default: /kubelet).")
 	fs.StringVar(&s.CgroupRoot, "cgroup-root", s.CgroupRoot, "Optional root cgroup to use for pods. This is handled by the container runtime on a best effort basis. Default: '', which means use the container runtime default.")
 	fs.StringVar(&s.ContainerRuntime, "container-runtime", s.ContainerRuntime, "The container runtime to use. Possible values: 'docker', 'rkt'. Default: 'docker'.")
+	fs.StringVar(&s.RktPath, "rkt-path", s.RktPath, "Path of rkt binary. Leave empty to use the first rkt in $PATH.  Only used if --container-runtime='rkt'")
 	fs.StringVar(&s.SystemContainer, "system-container", s.SystemContainer, "Optional resource-only container in which to place all non-kernel processes that are not already in a container. Empty for no container. Rolling back the flag requires a reboot. (Default: \"\").")
 	fs.BoolVar(&s.ConfigureCBR0, "configure-cbr0", s.ConfigureCBR0, "If true, kubelet will configure cbr0 based on Node.Spec.PodCIDR.")
 	fs.IntVar(&s.MaxPods, "max-pods", 40, "Number of Pods that can run on this Kubelet.")
@@ -348,6 +351,7 @@ func (s *KubeletServer) KubeletConfig() (*KubeletConfig, error) {
 		ResourceContainer:         s.ResourceContainer,
 		CgroupRoot:                s.CgroupRoot,
 		ContainerRuntime:          s.ContainerRuntime,
+		RktPath:                   s.RktPath,
 		Mounter:                   mounter,
 		DockerDaemonContainer:     s.DockerDaemonContainer,
 		SystemContainer:           s.SystemContainer,
@@ -753,6 +757,7 @@ type KubeletConfig struct {
 	OSInterface                    kubecontainer.OSInterface
 	CgroupRoot                     string
 	ContainerRuntime               string
+	RktPath                        string
 	Mounter                        mount.Interface
 	DockerDaemonContainer          string
 	SystemContainer                string
@@ -811,6 +816,7 @@ func createAndInitKubelet(kc *KubeletConfig) (k KubeletBootstrap, pc *config.Pod
 		kc.OSInterface,
 		kc.CgroupRoot,
 		kc.ContainerRuntime,
+		kc.RktPath,
 		kc.Mounter,
 		kc.DockerDaemonContainer,
 		kc.SystemContainer,