Kube Controller Manager 源码分析

Kube Controller Manager 源码分析

Controller Manager 在k8s 集群中扮演着中心管理的角色，它负责Deployment, StatefulSet, ReplicaSet 等资源的创建与管理，可以说是k8s的核心模块，下面我们以概略的形式走读一下k8s Controller Manager 代码。

func NewControllerManagerCommand() *cobra.Command {
    s, err := options.NewKubeControllerManagerOptions()
    if err != nil {
        klog.Fatalf("unable to initialize command options: %v", err)
    }

    cmd := &cobra.Command{
        Use: "kube-controller-manager",
        Long: `The Kubernetes controller manager is a daemon that embeds
the core control loops shipped with Kubernetes. In applications of robotics and
automation, a control loop is a non-terminating loop that regulates the state of
the system. In Kubernetes, a controller is a control loop that watches the shared
state of the cluster through the apiserver and makes changes attempting to move the
current state towards the desired state. Examples of controllers that ship with
Kubernetes today are the replication controller, endpoints controller, namespace
controller, and serviceaccounts controller.`,
        Run: func(cmd *cobra.Command, args []string) {
            verflag.PrintAndExitIfRequested()
            utilflag.PrintFlags(cmd.Flags())

            c, err := s.Config(KnownControllers(), ControllersDisabledByDefault.List())
            if err != nil {
                fmt.Fprintf(os.Stderr, "%v\n", err)
                os.Exit(1)
            }

            if err := Run(c.Complete(), wait.NeverStop); err != nil {
                fmt.Fprintf(os.Stderr, "%v\n", err)
                os.Exit(1)
            }
        },
    }

Controller Manager 也是一个命令行，通过一系列flag启动，具体的各个flag 我们就不多看，有兴趣的可以去文档或者flags_opinion.go 文件里面去过滤一下，我们直接从Run 函数入手。

Run Function 启动流程

Kube Controller Manager 既可以单实例启动，也可以多实例启动。 如果为了保证 HA 而启动多个Controller Manager，它就需要选主来保证同一时间只有一个Master 实例。我们来看一眼Run 函数的启动流程，这里会把一些不重要的细节函数略过，只看重点

func Run(c *config.CompletedConfig, stopCh  0 {
        if diff > rsc.burstReplicas {
            diff = rsc.burstReplicas
        }
        klog.V(2).Infof("Too many replicas for %v %s/%s, need %d, deleting %d", rsc.Kind, rs.Namespace, rs.Name, *(rs.Spec.Replicas), diff)

        // Choose which Pods to delete, preferring those in earlier phases of startup.
        podsToDelete := getPodsToDelete(filteredPods, diff)

        // Snapshot the UIDs (ns/name) of the pods we're expecting to see
        // deleted, so we know to record their expectations exactly once either
        // when we see it as an update of the deletion timestamp, or as a delete.
        // Note that if the labels on a pod/rs change in a way that the pod gets
        // orphaned, the rs will only wake up after the expectations have
        // expired even if other pods are deleted.
        rsc.expectations.ExpectDeletions(rsKey, getPodKeys(podsToDelete))

        errCh := make(chan error, diff)
        var wg sync.WaitGroup
        wg.Add(diff)
        for _, pod := range podsToDelete {
            go func(targetPod *v1.Pod) {
                defer wg.Done()
                if err := rsc.podControl.DeletePod(rs.Namespace, targetPod.Name, rs); err != nil {
                    // Decrement the expected number of deletes because the informer won't observe this deletion
                    podKey := controller.PodKey(targetPod)
                    klog.V(2).Infof("Failed to delete %v, decrementing expectations for %v %s/%s", podKey, rsc.Kind, rs.Namespace, rs.Name)
                    rsc.expectations.DeletionObserved(rsKey, podKey)
                    errCh  ReplicaSet -> Pod 就真正的创建完毕。当Pod 被删除时候，ReplicaSet Controller 就会把 Pod 拉起来。如果更新Deployment 就会创建新的ReplicaSet 一层层嵌套多个Controller 结合完成最终的 Pod 创建。 当然，这里其实仅仅完成了Pod 数据写入到ETCD，其实真正的 Pod 实例并没有创建，还需要scheduler & kubelet 配合完成，我们会在后面的章节继续介绍。
 
 
 
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