Kubernetes controller manager运行机制源码详细解析

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确立目标

理解 kube-controller-manager 的运行机制

从主函数找到 run 函数，代码较长，这里精简了一下

func Run(c *config.CompletedConfig, stopCh 
StartControllers
func StartControllers(ctx ControllerContext, startSATokenController InitFunc, controllers map[string]InitFunc, unsecuredMux *mux.PathRecorderMux) error {
    // 关键性的循环，启动每个 controllers，key 为控制器名字，value 为初始化函数
    for controllerName, initFn := range controllers {
    // 是否允许启动
        if !ctx.IsControllerEnabled(controllerName) {klog.Warningf("%q is disabled", controllerName)
            continue
        }
        time.Sleep(wait.Jitter(ctx.ComponentConfig.Generic.ControllerStartInterval.Duration, ControllerStartJitter))
        klog.V(1).Infof("Starting %q", controllerName)
    // 调用 init 函数进行启动
        debugHandler, started, err := initFn(ctx)
        if err != nil {klog.Errorf("Error starting %q", controllerName)
            return err
        }
        if !started {klog.Warningf("Skipping %q", controllerName)
            continue
        }
    // 注册对应 controller 到 debug 的 url 中
        if debugHandler != nil && unsecuredMux != nil {
            basePath := "/debug/controllers/" + controllerName
            unsecuredMux.UnlistedHandle(basePath, http.StripPrefix(basePath, debugHandler))
            unsecuredMux.UnlistedHandlePrefix(basePath+"/", http.StripPrefix(basePath, debugHandler))
        }
        klog.Infof("Started %q", controllerName)
    }
    return nil
}
// 我们再去传入 controller 的函数去看看，对应的 controller 有哪些，这里有我们很多常见的概念，不一一细讲
func NewControllerInitializers(loopMode ControllerLoopMode) map[string]InitFunc {controllers := map[string]InitFunc{}
    controllers["endpoint"] = startEndpointController
    controllers["endpointslice"] = startEndpointSliceController
    controllers["endpointslicemirroring"] = startEndpointSliceMirroringController
    controllers["replicationcontroller"] = startReplicationController
    controllers["podgc"] = startPodGCController
    controllers["resourcequota"] = startResourceQuotaController
    controllers["namespace"] = startNamespaceController
    controllers["serviceaccount"] = startServiceAccountController
    controllers["garbagecollector"] = startGarbageCollectorController
    controllers["daemonset"] = startDaemonSetController
    controllers["job"] = startJobController
    controllers["deployment"] = startDeploymentController
    controllers["replicaset"] = startReplicaSetController
    controllers["horizontalpodautoscaling"] = startHPAController
    controllers["disruption"] = startDisruptionController
    controllers["statefulset"] = startStatefulSetController
    controllers["cronjob"] = startCronJobController
    controllers["csrsigning"] = startCSRSigningController
    controllers["csrapproving"] = startCSRApprovingController
    controllers["csrcleaner"] = startCSRCleanerController
    controllers["ttl"] = startTTLController
    controllers["bootstrapsigner"] = startBootstrapSignerController
    controllers["tokencleaner"] = startTokenCleanerController
    controllers["nodeipam"] = startNodeIpamController
    controllers["nodelifecycle"] = startNodeLifecycleController
    if loopMode == IncludeCloudLoops {controllers["service"] = startServiceController
        controllers["route"] = startRouteController
        controllers["cloud-node-lifecycle"] = startCloudNodeLifecycleController
    }
    controllers["persistentvolume-binder"] = startPersistentVolumeBinderController
    controllers["attachdetach"] = startAttachDetachController
    controllers["persistentvolume-expander"] = startVolumeExpandController
    controllers["clusterrole-aggregation"] = startClusterRoleAggregrationController
    controllers["pvc-protection"] = startPVCProtectionController
    controllers["pv-protection"] = startPVProtectionController
    controllers["ttl-after-finished"] = startTTLAfterFinishedController
    controllers["root-ca-cert-publisher"] = startRootCACertPublisher
    controllers["ephemeral-volume"] = startEphemeralVolumeController
    return controllers
}
ReplicaSet
 由于我们的示例是创建一个 nginx 的 pod，涉及到 kube-controller-manager 的内容很少。
 但是，为了加深大家对 kube-controller-manager 的认识，我们引入一个新的概念 - ReplicaSet，下面是官方说明：
A ReplicaSet’s purpose is to maintain a stable set of replica Pods running at any given time. As such, it is often used to guarantee the availability of a specified number of identical Pods.
ReplicaSet 的目的是维护一组在任何时候都处于运行状态的 Pod 副本的稳定集合。因此，它通常用来保证给定数量的、完全相同的 Pod 的可用性。
 简单来说，ReplicaSet 就是用来生成指定个数的 Pod
 代码在 pkg/controller/replica_set.go
ReplicaSetController
func startReplicaSetController(ctx ControllerContext) (http.Handler, bool, error) {if !ctx.AvailableResources[schema.GroupVersionResource{Group: "apps", Version: "v1", Resource: "replicasets"}] {return nil, false, nil}
  // 用 goroutine 异步运行，包含了 ReplicaSet 和 Pod 的两个 Informer
  // 这一点很好理解：我们是要控制 ReplicaSet 声明的数量和运行的 Pod 数量一致，需要同时观察者两种资源
    go replicaset.NewReplicaSetController(ctx.InformerFactory.Apps().V1().ReplicaSets(),
        ctx.InformerFactory.Core().V1().Pods(),
        ctx.ClientBuilder.ClientOrDie("replicaset-controller"),
        replicaset.BurstReplicas,
    ).Run(int(ctx.ComponentConfig.ReplicaSetController.ConcurrentRSSyncs), ctx.Stop)
    return nil, true, nil
}
// 运行函数
func (rsc *ReplicaSetController) Run(workers int, stopCh 
syncReplicaSet
func (rsc *ReplicaSetController) syncReplicaSet(key string) error {startTime := time.Now()
    defer func() {klog.V(4).Infof("Finished syncing %v %q (%v)", rsc.Kind, key, time.Since(startTime))
    }()
    // 从 key 中拆分出 namespace 和 name
    namespace, name, err := cache.SplitMetaNamespaceKey(key)
    if err != nil {return err}
  // 根据 name，从 Lister 获取对应的 ReplicaSets 信息
    rs, err := rsc.rsLister.ReplicaSets(namespace).Get(name)
    if errors.IsNotFound(err) {klog.V(4).Infof("%v %v has been deleted", rsc.Kind, key)
        rsc.expectations.DeleteExpectations(key)
        return nil
    }
    if err != nil {return err}
    rsNeedsSync := rsc.expectations.SatisfiedExpectations(key)
  // 获取 selector (k8s 是根据 selector 中的 label 来匹配 ReplicaSets 和 Pod 的)
    selector, err := metav1.LabelSelectorAsSelector(rs.Spec.Selector)
    if err != nil {utilruntime.HandleError(fmt.Errorf("error converting pod selector to selector: %v", err))
        return nil
    }
    // 根据 namespace 和 labels 获取所有的 pod
    allPods, err := rsc.podLister.Pods(rs.Namespace).List(labels.Everything())
    if err != nil {return err}
        // 过滤无效的 pod
    filteredPods := controller.FilterActivePods(allPods)
    // 根据 selector 再过滤 pod
    filteredPods, err = rsc.claimPods(rs, selector, filteredPods)
    if err != nil {return err}
    var manageReplicasErr error
    if rsNeedsSync && rs.DeletionTimestamp == nil {
    // 管理 ReplicaSet，下面详细分析
        manageReplicasErr = rsc.manageReplicas(filteredPods, rs)
    }
    rs = rs.DeepCopy()
    newStatus := calculateStatus(rs, filteredPods, manageReplicasErr)
    // 更新状态
    updatedRS, err := updateReplicaSetStatus(rsc.kubeClient.AppsV1().ReplicaSets(rs.Namespace), rs, newStatus)
    if err != nil {return err}
    if manageReplicasErr == nil && updatedRS.Spec.MinReadySeconds > 0 &&
        updatedRS.Status.ReadyReplicas == *(updatedRS.Spec.Replicas) &&
        updatedRS.Status.AvailableReplicas != *(updatedRS.Spec.Replicas) {rsc.queue.AddAfter(key, time.Duration(updatedRS.Spec.MinReadySeconds)*time.Second)
    }
    return manageReplicasErr
}
// 我们再一起看看，当 Pod 数量和 ReplicaSet 中声明的不同时，是怎么工作的
func (rsc *ReplicaSetController) manageReplicas(filteredPods []*v1.Pod, rs *apps.ReplicaSet) error {
    // diff = 当前 pod 数 - 期望 pod 数
  diff := len(filteredPods) - int(*(rs.Spec.Replicas))
    rsKey, err := controller.KeyFunc(rs)
    if err != nil {utilruntime.HandleError(fmt.Errorf("couldn't get key for %v %#v: %v", rsc.Kind, rs, err))
        return nil
    }
  // diff 小于 0，表示需要扩容，即新增 Pod
    if diff  0 { }
    return nil
}
站在前人的肩膀上，向前辈致敬，Respect！
Summary
kube-controller-manager 的核心思想是：根据期望状态和当前状态，管理 Kubernetes 中的资源。以 ReplicaSet 为例，它对比了定义声明的 Pod 数和当前集群中满足条件的 Pod 数，进行相对应的扩缩容。
 
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