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daemonset controller 源码分析
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在 minkube 上部署 knative
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<li><a href="#daemonset-的基本操作">DaemonSet 的基本操作</a><ul>
<li><a href="#创建">创建</a></li>
<li><a href="#扩缩容">扩缩容</a></li>
<li><a href="#更新">更新</a></li>
<li><a href="#回滚">回滚</a></li>
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<li><a href="#daemonsetcontroller-源码分析">DaemonSetController 源码分析</a><ul>
<li><a href="#syncdaemonset">syncDaemonSet</a></li>
<li><a href="#manage">manage</a><ul>
<li><a href="#getnodestodaemonpods">getNodesToDaemonPods</a></li>
<li><a href="#podsshouldbeonnode">podsShouldBeOnNode</a></li>
<li><a href="#syncnodes">syncNodes</a></li>
</ul>
</li>
<li><a href="#rollingupdate">RollingUpdate</a></li>
<li><a href="#updatedaemonsetstatus">updateDaemonSetStatus</a></li>
</ul>
</li>
<li><a href="#总结">总结</a></li>
</ul>
<p>在前面的文章中已经分析过 deployment、statefulset 两个重要对象了，本文会继续分析 kubernetes 中另一个重要的对象 daemonset，在 kubernetes 中 daemonset 类似于 linux 上的守护进程会运行在每一个 node 上，在实际场景中，一般会将日志采集或者网络插件采用 daemonset 的方式部署。</p>
<h3 id="daemonset-的基本操作"><a name="daemonset-的基本操作" class="anchor-navigation-ex-anchor" href="#daemonset-的基本操作"><i class="fa fa-link" aria-hidden="true"></i></a>DaemonSet 的基本操作</h3>
<h4 id="创建"><a name="创建" class="anchor-navigation-ex-anchor" href="#创建"><i class="fa fa-link" aria-hidden="true"></i></a>创建</h4>
<p>daemonset 在创建后会在每个 node 上都启动一个 pod。</p>
<pre class="language-"><code>$ kubectl create -f nginx-ds.yaml
</code></pre><h4 id="扩缩容"><a name="扩缩容" class="anchor-navigation-ex-anchor" href="#扩缩容"><i class="fa fa-link" aria-hidden="true"></i></a>扩缩容</h4>
<p>由于 daemonset 是在每个 node 上启动一个 pod，其不存在扩缩容操作，副本数量跟 node 数量保持一致。</p>
<h4 id="更新"><a name="更新" class="anchor-navigation-ex-anchor" href="#更新"><i class="fa fa-link" aria-hidden="true"></i></a>更新</h4>
<p>daemonset 有两种更新策略 <code>OnDelete</code> 和 <code>RollingUpdate</code>，默认为 <code>RollingUpdate</code>。滚动更新时，需要指定 <code>.spec.updateStrategy.rollingUpdate.maxUnavailable</code>（默认为1）和 <code>.spec.minReadySeconds</code>（默认为 0）。</p>
<pre class="language-"><code>// 更新镜像
$ kubectl set image ds/nginx-ds nginx-ds=nginx:1.16
// 查看更新状态
$ kubectl rollout status ds/nginx-ds
</code></pre><h4 id="回滚"><a name="回滚" class="anchor-navigation-ex-anchor" href="#回滚"><i class="fa fa-link" aria-hidden="true"></i></a>回滚</h4>
<p>在 statefulset 源码分析一节已经提到过 <code>controllerRevision</code> 这个对象了，其主要用来保存历史版本信息，在更新以及回滚操作时使用，daemonset controller 也是使用 <code>controllerrevision</code> 保存历史版本信息，在回滚时会使用历史 <code>controllerrevision</code> 中的信息替换 daemonset 中 <code>Spec.Template</code>。</p>
<pre class="language-"><code>// 查看 ds 历史版本信息
$ kubectl get controllerrevision
NAME CONTROLLER REVISION AGE
nginx-ds-5c4b75bdbb daemonset.apps/nginx-ds 2 122m
nginx-ds-7cd7798dcd daemonset.apps/nginx-ds 1 133m
// 回滚到版本 1
$ kubectl rollout undo daemonset nginx-ds --to-revision=1
// 查看回滚状态
$ kubectl rollout status ds/nginx-ds
</code></pre><h4 id="暂停"><a name="暂停" class="anchor-navigation-ex-anchor" href="#暂停"><i class="fa fa-link" aria-hidden="true"></i></a>暂停</h4>
<p>daemonset 目前不支持暂停操作。</p>
<h4 id="删除"><a name="删除" class="anchor-navigation-ex-anchor" href="#删除"><i class="fa fa-link" aria-hidden="true"></i></a>删除</h4>
<p>daemonset 也支持两种删除操作。</p>
<pre class="language-"><code>// 非级联删除
$ kubectl delete ds/nginx-ds --cascade=false
// 级联删除
$ kubectl delete ds/nginx-ds
</code></pre><h3 id="daemonsetcontroller-源码分析"><a name="daemonsetcontroller-源码分析" class="anchor-navigation-ex-anchor" href="#daemonsetcontroller-源码分析"><i class="fa fa-link" aria-hidden="true"></i></a>DaemonSetController 源码分析</h3>
<blockquote>
<p>kubernetes 版本：v1.16</p>
</blockquote>
<p>首先还是看 <code>startDaemonSetController</code> 方法，在此方法中会初始化 <code>DaemonSetsController</code> 对象并调用 <code>Run</code>方法启动 daemonset controller，从该方法中可以看出 daemonset controller 会监听 <code>daemonsets</code>、<code>controllerRevision</code>、<code>pod</code> 和 <code>node</code> 四种对象资源的变动。其中 <code>ConcurrentDaemonSetSyncs</code>的默认值为 2。</p>
<p><code>k8s.io/kubernetes/cmd/kube-controller-manager/app/apps.go:36</code></p>
<pre class="language-"><code>func startDaemonSetController(ctx ControllerContext) (http.Handler, bool, error) {
if !ctx.AvailableResources[schema.GroupVersionResource{Group: "apps", Version: "v1", Resource: "daemonsets"}] {
return nil, false, nil
}
dsc, err := daemon.NewDaemonSetsController(
ctx.InformerFactory.Apps().V1().DaemonSets(),
ctx.InformerFactory.Apps().V1().ControllerRevisions(),
ctx.InformerFactory.Core().V1().Pods(),
ctx.InformerFactory.Core().V1().Nodes(),
ctx.ClientBuilder.ClientOrDie("daemon-set-controller"),
flowcontrol.NewBackOff(1*time.Second, 15*time.Minute),
)
if err != nil {
return nil, true, fmt.Errorf("error creating DaemonSets controller: %v", err)
}
go dsc.Run(int(ctx.ComponentConfig.DaemonSetController.ConcurrentDaemonSetSyncs), ctx.Stop)
return nil, true, nil
}
</code></pre><p>在 <code>Run</code> 方法中会启动两个操作，一个就是 <code>dsc.runWorker</code> 执行的 sync 操作，另一个就是 <code>dsc.failedPodsBackoff.GC</code> 执行的 gc 操作，主要逻辑为：</p>
<ul>
<li>1、等待 informer 缓存同步完成；</li>
<li>2、启动两个 goroutine 分别执行 <code>dsc.runWorker</code>；</li>
<li>3、启动一个 goroutine 每分钟执行一次 <code>dsc.failedPodsBackoff.GC</code>，从 <code>startDaemonSetController</code> 方法中可以看到 <code>failedPodsBackoff</code> 的 duration为1s，max duration为15m，<code>failedPodsBackoff</code> 的主要作用是当发现 daemon pod 状态为 failed 时，会定时重启该 pod；</li>
</ul>
<p><code>k8s.io/kubernetes/pkg/controller/daemon/daemon_controller.go:263</code></p>
<pre class="language-"><code>func (dsc *DaemonSetsController) Run(workers int, stopCh <-chan struct{}) {
defer utilruntime.HandleCrash()
defer dsc.queue.ShutDown()
defer klog.Infof("Shutting down daemon sets controller")
if !cache.WaitForNamedCacheSync("daemon sets", stopCh, dsc.podStoreSynced, dsc.nodeStoreSynced, dsc.historyStoreSynced, dsc.dsStoreSynced) {
return
}
for i := 0; i < workers; i++ {
// sync 操作
go wait.Until(dsc.runWorker, time.Second, stopCh)
}
// GC 操作
go wait.Until(dsc.failedPodsBackoff.GC, BackoffGCInterval, stopCh)
<-stopCh
}
</code></pre><h4 id="syncdaemonset"><a name="syncdaemonset" class="anchor-navigation-ex-anchor" href="#syncdaemonset"><i class="fa fa-link" aria-hidden="true"></i></a>syncDaemonSet</h4>
<p>daemonset 中 pod 的创建与删除是与 node 相关联的，所以每次执行 sync 操作时需要遍历所有的 node 进行判断。<code>syncDaemonSet</code> 的主要逻辑为：</p>
<ul>
<li>1、通过 key 获取 ns 和 name；</li>
<li>2、从 dsLister 中获取 ds 对象；</li>
<li>3、从 nodeLister 获取所有 node；</li>
<li>4、获取 dsKey；</li>
<li>5、判断 ds 是否处于删除状态；</li>
<li>6、调用 <code>constructHistory</code> 获取 current 和 old <code>controllerRevision</code>；</li>
<li>7、调用 <code>dsc.expectations.SatisfiedExpectations</code> 判断是否满足 <code>expectations</code> 机制，<code>expectations</code> 机制的目的就是减少不必要的 sync 操作，关于 <code>expectations</code> 机制的详细说明可以参考笔者以前写的 "replicaset controller 源码分析"一文；</li>
<li>8、调用 <code>dsc.manage</code> 执行实际的 sync 操作；</li>
<li>9、判断是否为更新操作，并执行对应的更新操作逻辑；</li>
<li>10、调用 <code>dsc.cleanupHistory</code> 根据 <code>spec.revisionHistoryLimit</code>字段清理过期的 <code>controllerrevision</code>；</li>
<li>11、调用 <code>dsc.updateDaemonSetStatus</code> 更新 ds 状态； </li>
</ul>
<p><code>k8s.io/kubernetes/pkg/controller/daemon/daemon_controller.go:1212</code></p>
<pre class="language-"><code>func (dsc *DaemonSetsController) syncDaemonSet(key string) error {
......
// 1、通过 key 获取 ns 和 name
namespace, name, err := cache.SplitMetaNamespaceKey(key)
if err != nil {
return err
}
// 2、从 dsLister 中获取 ds 对象
ds, err := dsc.dsLister.DaemonSets(namespace).Get(name)
if errors.IsNotFound(err) {
dsc.expectations.DeleteExpectations(key)
return nil
}
......
// 3、从 nodeLister 获取所有 node
nodeList, err := dsc.nodeLister.List(labels.Everything())
......
everything := metav1.LabelSelector{}
if reflect.DeepEqual(ds.Spec.Selector, &everything) {
dsc.eventRecorder.Eventf(ds, v1.EventTypeWarning, SelectingAllReason, "This daemon set is selecting all pods. A non-empty selector is required. ")
return nil
}