Add RuntimeHooks interface and Kubelet implementation.

This interface will be used to inject functionality and logic into the
runtimes that should be shared accross runtimes.

pkg/kubelet/container/runtime.go

@@ -81,6 +81,16 @@ type Runtime interface {
 	GetContainerLogs(containerID, tail string, follow bool, stdout, stderr io.Writer) (err error)
 }
 
+// Customizable hooks injected into container runtimes.
+type RuntimeHooks interface {
+	// Determines whether the runtime should pull the specified container's image.
+	ShouldPullImage(pod *api.Pod, container *api.Container, imagePresent bool) bool
+
+	// Runs after an image is pulled reporting it's status. Error may be nil
+	// for a successful pull.
+	ReportImagePull(pod *api.Pod, container *api.Container, err error)
+}
+
 // Pod is a group of containers, with the status of the pod.
 type Pod struct {
 	// The ID of the pod, which can be used to retrieve a particular pod

pkg/kubelet/runtime_hooks.go

@@ -0,0 +1,64 @@
+/*
+Copyright 2015 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package kubelet
+
+import (
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/client/record"
+	kubecontainer "github.com/GoogleCloudPlatform/kubernetes/pkg/kubelet/container"
+	"github.com/golang/glog"
+)
+
+// Kubelet-specific runtime hooks.
+type kubeletRuntimeHooks struct {
+	recorder record.EventRecorder
+}
+
+var _ kubecontainer.RuntimeHooks = &kubeletRuntimeHooks{}
+
+func newKubeletRuntimeHooks(recorder record.EventRecorder) kubecontainer.RuntimeHooks {
+	return &kubeletRuntimeHooks{
+		recorder: recorder,
+	}
+}
+
+func (kr *kubeletRuntimeHooks) ShouldPullImage(pod *api.Pod, container *api.Container, imagePresent bool) bool {
+	if container.ImagePullPolicy == api.PullNever {
+		return false
+	}
+
+	if container.ImagePullPolicy == api.PullAlways ||
+		(container.ImagePullPolicy == api.PullIfNotPresent && (!imagePresent)) {
+		return true
+	}
+
+	return false
+}
+
+func (kr *kubeletRuntimeHooks) ReportImagePull(pod *api.Pod, container *api.Container, err error) {
+	ref, err := kubecontainer.GenerateContainerRef(pod, container)
+	if err != nil {
+		glog.Errorf("Couldn't make a ref to pod %v, container %v: '%v'", pod.Name, container.Name, err)
+		return
+	}
+
+	if err != nil {
+		kr.recorder.Eventf(ref, "failed", "Failed to pull image %q: %v", container.Image, err)
+	} else {
+		kr.recorder.Eventf(ref, "pulled", "Successfully pulled image %q", container.Image)
+	}
+}