Introduce DockerCache in Kubelet.

pkg/kubelet/dockertools/docker_cache.go

+/*
+Copyright 2014 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 dockertools
+
+import (
+	"sync"
+	"time"
+)
+
+type DockerCache interface {
+	RunningContainers() (DockerContainers, error)
+}
+
+func NewDockerCache(client DockerInterface) (DockerCache, error) {
+	containers, err := GetKubeletDockerContainers(client, false)
+	if err != nil {
+		return nil, err
+	}
+	return &dockerCache{
+		client:        client,
+		cacheTime:     time.Now(),
+		containers:    containers,
+		updatingCache: false,
+	}, nil
+}
+
+// dockerCache is a default implementation of DockerCache interface
+type dockerCache struct {
+	// The underlying docker client used to update the cache.
+	client DockerInterface
+
+	// Mutex protecting all of the following fields.
+	lock sync.Mutex
+	// Last time when cache was updated.
+	cacheTime time.Time
+	// The content of the cache.
+	containers DockerContainers
+	// Whether the background thread updating the cache is running.
+	updatingCache bool
+	// Time when the background thread should be stopped.
+	updatingThreadStopTime time.Time
+}
+
+func (d *dockerCache) RunningContainers() (DockerContainers, error) {
+	d.lock.Lock()
+	defer d.lock.Unlock()
+	if time.Since(d.cacheTime) > 2*time.Second {
+		containers, err := GetKubeletDockerContainers(d.client, false)
+		if err != nil {
+			return containers, err
+		}
+		d.containers = containers
+		d.cacheTime = time.Now()
+	}
+	// Stop refreshing thread if there were no requests within last 2 seconds.
+	d.updatingThreadStopTime = time.Now().Add(time.Duration(2) * time.Second)
+	if !d.updatingCache {
+		d.updatingCache = true
+		go d.startUpdatingCache()
+	}
+	return d.containers, nil
+}
+
+func (d *dockerCache) startUpdatingCache() {
+	run := true
+	for run {
+		time.Sleep(100 * time.Millisecond)
+		containers, err := GetKubeletDockerContainers(d.client, false)
+		cacheTime := time.Now()
+		if err != nil {
+			continue
+		}
+
+		d.lock.Lock()
+		if time.Now().After(d.updatingThreadStopTime) {
+			d.updatingCache = false
+			run = false
+		}
+		d.containers = containers
+		d.cacheTime = cacheTime
+		d.lock.Unlock()
+	}
+}

pkg/kubelet/dockertools/fake_docker_client.go

@@ -232,3 +232,17 @@ func (f *FakeDockerPuller) IsImagePresent(name string) (bool, error) {
 	}
 	return false, nil
 }
+
+type FakeDockerCache struct {
+	client DockerInterface
+}
+
+func NewFakeDockerCache(client DockerInterface) DockerCache {
+	return &FakeDockerCache{
+		client: client,
+	}
+}
+
+func (f *FakeDockerCache) RunningContainers() (DockerContainers, error) {
+	return GetKubeletDockerContainers(f.client, false)
+}

pkg/kubelet/kubelet.go

@@ -128,10 +128,16 @@ func NewMainKubelet(
 		streamingConnectionIdleTimeout: streamingConnectionIdleTimeout,
 	}
 
-	if err := klet.setupDataDirs(); err != nil {
+	dockerCache, err := dockertools.NewDockerCache(dockerClient)
+	if err != nil {
 		return nil, err
 	}
-	if err := klet.volumePluginMgr.InitPlugins(volumePlugins, &volumeHost{klet}); err != nil {
+	klet.dockerCache = dockerCache
+
+	if err = klet.setupDataDirs(); err != nil {
+		return nil, err
+	}
+	if err = klet.volumePluginMgr.InitPlugins(volumePlugins, &volumeHost{klet}); err != nil {
 		return nil, err
 	}
 
@@ -150,6 +156,7 @@ type serviceLister interface {
 type Kubelet struct {
 	hostname               string
 	dockerClient           dockertools.DockerInterface
+	dockerCache            dockertools.DockerCache
 	kubeClient             *client.Client
 	rootDirectory          string
 	podInfraContainerImage string
@@ -1300,7 +1307,7 @@ func (kl *Kubelet) SyncPods(pods []api.BoundPod) error {
 	desiredContainers := make(map[podContainer]empty)
 	desiredPods := make(map[types.UID]empty)
 
-	dockerContainers, err := dockertools.GetKubeletDockerContainers(kl.dockerClient, false)
+	dockerContainers, err := kl.dockerCache.RunningContainers()
 	if err != nil {
 		glog.Errorf("Error listing containers: %#v", dockerContainers)
 		return err

pkg/kubelet/kubelet_test.go

@@ -55,6 +55,7 @@ func newTestKubelet(t *testing.T) (*Kubelet, *dockertools.FakeDockerClient) {
 
 	kubelet := &Kubelet{}
 	kubelet.dockerClient = fakeDocker
+	kubelet.dockerCache = dockertools.NewFakeDockerCache(fakeDocker)
 	kubelet.dockerPuller = &dockertools.FakeDockerPuller{}
 	if tempDir, err := ioutil.TempDir("/tmp", "kubelet_test."); err != nil {
 		t.Fatalf("can't make a temp rootdir: %v", err)