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<title>garbage collector controller 源码分析 · 田飞雨</title>
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kube-scheduler predicates 与 priorities 调度算法源码分析
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kube-scheduler 优先级与抢占机制源码分析
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kubelet 中垃圾回收机制的设计与实现
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kubernetes 中 Evicted pod 是如何产生的
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在 minkube 上部署 knative
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</li>
<li><a href="#garbagecollectorrun">garbageCollector.Run</a><ul>
<li><a href="#gcdependencygraphbuilderrun">gc.dependencyGraphBuilder.Run</a><ul>
<li><a href="#uidtonode">uidToNode</a></li>
<li><a href="#gbstartmonitors">gb.startMonitors</a></li>
<li><a href="#gbrunprocessgraphchanges">gb.runProcessGraphChanges</a></li>
<li><a href="#processtransitions">processTransitions</a></li>
</ul>
</li>
<li><a href="#gcrunattempttodeleteworker">gc.runAttemptToDeleteWorker</a><ul>
<li><a href="#gcattempttodeleteitem">gc.attemptToDeleteItem</a></li>
</ul>
</li>
<li><a href="#gcrunattempttoorphanworker">gc.runAttemptToOrphanWorker</a></li>
</ul>
</li>
<li><a href="#garbagecollectorsync">garbageCollector.Sync</a><ul>
<li><a href="#getdeletableresources">GetDeletableResources</a><ul>
<li><a href="#serverpreferredresources">ServerPreferredResources</a></li>
</ul>
</li>
<li><a href="#gcresyncmonitors">gc.resyncMonitors</a></li>
</ul>
</li>
<li><a href="#garbagecollectornewdebughandler">garbagecollector.NewDebugHandler</a></li>
</ul>
</li>
<li><a href="#示例">示例</a></li>
<li><a href="#总结">总结</a></li>
</ul>
<p>在前面几篇关于 controller 源码分析的文章中多次提到了当删除一个对象时，其对应的 controller 并不会执行删除对象的操作，在 kubernetes 中对象的回收操作是由 GarbageCollectorController 负责的，其作用就是当删除一个对象时，会根据指定的删除策略回收该对象及其依赖对象，本文会深入分析垃圾收集背后的实现。</p>
<h3 id="kubernetes-中的删除策略"><a name="kubernetes-中的删除策略" class="anchor-navigation-ex-anchor" href="#kubernetes-中的删除策略"><i class="fa fa-link" aria-hidden="true"></i></a>kubernetes 中的删除策略</h3>
<p>kubernetes 中有三种删除策略：<code>Orphan</code>、<code>Foreground</code> 和 <code>Background</code>，三种删除策略的意义分别为：</p>
<ul>
<li><code>Orphan</code> 策略：非级联删除，删除对象时，不会自动删除它的依赖或者是子对象，这些依赖被称作是原对象的孤儿对象，例如当执行以下命令时会使用 <code>Orphan</code> 策略进行删除，此时 ds 的依赖对象 <code>controllerrevision</code> 不会被删除；</li>
</ul>
<pre class="language-"><code>$ kubectl delete ds/nginx-ds --cascade=false
</code></pre><ul>
<li><p><code>Background</code> 策略：在该模式下，kubernetes 会立即删除该对象，然后垃圾收集器会在后台删除这些该对象的依赖对象；</p>
</li>
<li><p><code>Foreground</code> 策略：在该模式下，对象首先进入“删除中”状态，即会设置对象的 <code>deletionTimestamp</code> 字段并且对象的 <code>metadata.finalizers</code> 字段包含了值 “foregroundDeletion”，此时该对象依然存在，然后垃圾收集器会删除该对象的所有依赖对象，垃圾收集器在删除了所有“Blocking” 状态的依赖对象（指其子对象中 <code>ownerReference.blockOwnerDeletion=true</code>的对象）之后，然后才会删除对象本身；</p>
</li>
</ul>
<p>在 v1.9 以前的版本中，大部分 controller 默认的删除策略为 <code>Orphan</code>，从 v1.9 开始，对于 apps/v1 下的资源默认使用 <code>Background</code> 模式。以上三种删除策略都可以在删除对象时通过设置 <code>deleteOptions.propagationPolicy</code> 字段进行指定，如下所示：</p>
<pre class="language-"><code>$ curl -k -v -XDELETE -H "Accept: application/json" -H "Content-Type: application/json" -d '{"propagationPolicy":"Foreground"}' 'https://192.168.99.108:8443/apis/apps/v1/namespaces/default/daemonsets/nginx-ds'
</code></pre><h4 id="finalizer-机制"><a name="finalizer-机制" class="anchor-navigation-ex-anchor" href="#finalizer-机制"><i class="fa fa-link" aria-hidden="true"></i></a>finalizer 机制</h4>
<p>finalizer 是在删除对象时设置的一个 hook，其目的是为了让对象在删除前确认其子对象已经被完全删除，k8s 中默认有两种 finalizer：<code>OrphanFinalizer</code> 和 <code>ForegroundFinalizer</code>，finalizer 存在于对象的 ObjectMeta 中，当一个对象的依赖对象被删除后其对应的 finalizers 字段也会被移除，只有 finalizers 字段为空时，apiserver 才会删除该对象。</p>
<pre class="language-"><code>{
......
"metadata": {
......
"finalizers": [
"foregroundDeletion"
]
}
......
}
</code></pre><p>此外，finalizer 不仅仅支持以上两种字段，在使用自定义 controller 时也可以在 CR 中设置自定义的 finalizer 标识。</p>
<h3 id="garbagecollectorcontroller-源码分析"><a name="garbagecollectorcontroller-源码分析" class="anchor-navigation-ex-anchor" href="#garbagecollectorcontroller-源码分析"><i class="fa fa-link" aria-hidden="true"></i></a>GarbageCollectorController 源码分析</h3>
<blockquote>
<p>kubernetes 版本：v1.16</p>
</blockquote>
<p>GarbageCollectorController 负责回收 kubernetes 中的资源，要回收 kubernetes 中所有资源首先得监控所有资源，GarbageCollectorController 会监听集群中所有可删除资源产生的所有事件，这些事件会被放入到一个队列中，然后 controller 会启动多个 goroutine 处理队列中的事件，若为删除事件会根据对象的删除策略删除关联的对象，对于非删除事件会更新对象之间的依赖关系。</p>
<h4 id="startgarbagecollectorcontroller"><a name="startgarbagecollectorcontroller" class="anchor-navigation-ex-anchor" href="#startgarbagecollectorcontroller"><i class="fa fa-link" aria-hidden="true"></i></a>startGarbageCollectorController</h4>
<p>首先还是看 GarbageCollectorController 的启动方法 <code>startGarbageCollectorController</code>，其主要逻辑为：</p>
<ul>
<li>1、初始化 discoveryClient，discoveryClient 主要用来获取集群中的所有资源； </li>
<li>2、调用 <code>garbagecollector.GetDeletableResources</code> 获取集群内所有可删除的资源对象，支持 "delete", "list", "watch" 三种操作的 resource 称为 <code>deletableResource</code>；</li>
<li>3、调用 <code>garbagecollector.NewGarbageCollector</code> 初始化 garbageCollector 对象；</li>
<li>4、调用 <code>garbageCollector.Run</code> 启动 garbageCollector；</li>
<li>5、调用 <code>garbageCollector.Sync</code> 监听集群中的 <code>DeletableResources</code> ，当出现新的 <code>DeletableResources</code> 时同步到 monitors 中，确保监控集群中的所有资源；</li>
<li>6、调用 <code>garbagecollector.NewDebugHandler</code> 注册 debug 接口，用来提供集群内所有对象的关联关系；</li>
</ul>
<p><code>k8s.io/kubernetes/cmd/kube-controller-manager/app/core.go:443</code></p>
<pre class="language-"><code>func startGarbageCollectorController(ctx ControllerContext) (http.Handler, bool, error) {
if !ctx.ComponentConfig.GarbageCollectorController.EnableGarbageCollector {
return nil, false, nil
}
// 1、初始化 discoveryClient
gcClientset := ctx.ClientBuilder.ClientOrDie("generic-garbage-collector")
discoveryClient := cacheddiscovery.NewMemCacheClient(gcClientset.Discovery())
config := ctx.ClientBuilder.ConfigOrDie("generic-garbage-collector")
metadataClient, err := metadata.NewForConfig(config)
if err != nil {
return nil, true, err
}
// 2、获取 deletableResource
deletableResources := garbagecollector.GetDeletableResources(discoveryClient)
ignoredResources := make(map[schema.GroupResource]struct{})
for _, r := range ctx.ComponentConfig.GarbageCollectorController.GCIgnoredResources {
ignoredResources[schema.GroupResource{Group: r.Group, Resource: r.Resource}] = struct{}{}
}
// 3、初始化 garbageCollector 对象
garbageCollector, err := garbagecollector.NewGarbageCollector(
......
)
if err != nil {
return nil, true, fmt.Errorf("failed to start the generic garbage collector: %v", err)
}
// 4、启动 garbage collector
workers := int(ctx.ComponentConfig.GarbageCollectorController.ConcurrentGCSyncs)
go garbageCollector.Run(workers, ctx.Stop)
// 5、监听集群中的 DeletableResources
go garbageCollector.Sync(gcClientset.Discovery(), 30*time.Second, ctx.Stop)
// 6、注册 debug 接口
return garbagecollector.NewDebugHandler(garbageCollector), true, nil
}
</code></pre><p>在 <code>startGarbageCollectorController</code> 中主要调用了四种方法<code>garbagecollector.NewGarbageCollector</code>、<code>garbageCollector.Run</code>、<code>garbageCollector.Sync</code> 和 <code>garbagecollector.NewDebugHandler</code> 来完成核心功能，下面主要针对这四种方法进行说明。</p>
<h4 id="garbagecollectornewgarbagecollector"><a name="garbagecollectornewgarbagecollector" class="anchor-navigation-ex-anchor" href="#garbagecollectornewgarbagecollector"><i class="fa fa-link" aria-hidden="true"></i></a>garbagecollector.NewGarbageCollector</h4>
<p><code>NewGarbageCollector</code> 的主要功能是初始化 GarbageCollector 和 GraphBuilder 对象，并调用 <code>gb.syncMonitors</code>方法初始化 deletableResources 中所有 resource controller 的 informer。GarbageCollector 的主要作用是启动 GraphBuilder 以及启动所有的消费者，GraphBuilder 的主要作用是启动所有的生产者。</p>
<p><code>k8s.io/kubernetes/pkg/controller/garbagecollector/garbagecollector.go:74</code></p>
<pre class="language-"><code>func NewGarbageCollector(......) (*GarbageCollector, error) {
......
gc := &GarbageCollector{
......
}
gb := &GraphBuilder{
......
}
if err := gb.syncMonitors(deletableResources); err != nil {
utilruntime.HandleError(fmt.Errorf("failed to sync all monitors: %v", err))
}
gc.dependencyGraphBuilder = gb
return gc, nil
}
</code></pre><h5 id="gbsyncmonitors"><a name="gbsyncmonitors" class="anchor-navigation-ex-anchor" href="#gbsyncmonitors"><i class="fa fa-link" aria-hidden="true"></i></a>gb.syncMonitors</h5>
<p><code>syncMonitors</code> 的主要作用是初始化各个资源对象的 informer，并调用 <code>gb.controllerFor</code> 为每种资源注册 eventHandler，此处每种资源被称为 monitors，因为为每种资源注册 eventHandler 时，对于 AddFunc、UpdateFunc 和 DeleteFunc 都会将对应的 event push 到 graphChanges 队列中，每种资源对象的 informer 都作为生产者。</p>
<p><code>k8s.io/kubernetes/pkg/controller/garbagecollector/graph_builder.go:179</code></p>
<pre class="language-"><code>func (gb *GraphBuilder) syncMonitors(resources map[schema.GroupVersionResource]struct{}) error {
gb.monitorLock.Lock()
defer gb.monitorLock.Unlock()
......
for resource := range resources {
if _, ok := gb.ignoredResources[resource.GroupResource()]; ok {