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<div><h1>14 庖丁解牛：controller-manager</h1>
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||
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<h2>整体概览</h2>
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||
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<pre><code>+----------------------------------------------------------+
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| Master |
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| +-------------------------+ |
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| +------->| API Server |<--------+ |
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| | | | | |
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| v +-------------------------+ v |
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||
| +----------------+ ^ +--------------------+ |
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| | | | | | |
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| | Scheduler | | | Controller Manager | |
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| | | | | | |
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| +----------------+ v +--------------------+ |
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| +------------------------------------------------------+ |
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| | | |
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| | Cluster state store | |
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| | | |
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| +------------------------------------------------------+ |
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+----------------------------------------------------------+
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</code></pre>
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||
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<p>在第 3 节《宏观认识：整体架构》 中，我们也认识到了 <code>Controller Manager</code> 的存在，知道了 Master 是 K8S 是集群的大脑，而它则是 Master 中最繁忙的部分。为什么这么说？本节我们一同来看看它为何如此繁忙。</p>
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||
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<p><strong>注意：Controller Manager 实际由 kube-controller-manager 和 cloud-controller-manager 两部分组成，cloud-controller-manager 则是为各家云厂商提供了一个抽象的封装，便于让各厂商使用各自的 provide。本文只讨论 kube-controller-manager，为了避免混淆，下文统一使用 kube-controller-manager。</strong></p>
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<h2><code>kube-controller-manager</code> 是什么</h2>
|
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|
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<p>一句话来讲 <code>kube-controller-manager</code> 是一个嵌入了 K8S 核心控制循环的守护进程。</p>
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<p>这里的重点是</p>
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<ul>
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<li>嵌入：它已经内置了相关逻辑，可独立进行部署。我们在第 5 节下载 K8S 服务端二进制文件解压后，便可以看到 <code>kube-controller-manager</code> 的可执行文件，不过我们使用的是 <code>kubeadm</code> 进行的部署，它会默认使用 <code>k8s.gcr.io/kube-controller-manager</code> 的镜像。我们直接来看下实际情况：</li>
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</ul>
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<pre><code>master $ kubectl -n kube-system describe pods -l component=kube-controller-manager
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Name: kube-controller-manager-master
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Namespace: kube-system
|
||
|
||
Priority: 2000000000
|
||
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||
PriorityClassName: system-cluster-critical
|
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|
||
Node: master/172.17.0.35
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||
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||
Start Time: Mon, 10 Dec 2018 07:14:21 +0000
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||
|
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Labels: component=kube-controller-manager
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|
||
tier=control-plane
|
||
|
||
Annotations: kubernetes.io/config.hash=c7ed7a8fa5c430410e84970f8ee7e067
|
||
|
||
kubernetes.io/config.mirror=c7ed7a8fa5c430410e84970f8ee7e067
|
||
|
||
kubernetes.io/config.seen=2018-12-10T07:14:21.685626322Z
|
||
|
||
kubernetes.io/config.source=file
|
||
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||
scheduler.alpha.kubernetes.io/critical-pod=
|
||
|
||
Status: Running
|
||
|
||
IP: 172.17.0.35
|
||
|
||
Containers:
|
||
|
||
kube-controller-manager:
|
||
|
||
Container ID: docker://0653e71ae4287608726490b724c3d064d5f1556dd89b7d3c618e97f0e7f2a533
|
||
|
||
Image: k8s.gcr.io/kube-controller-manager-amd64:v1.11.3
|
||
|
||
Image ID: docker-pullable://k8s.gcr.io/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="563d2334337b3539382224393a3a33247b3b3738373133247b373b32606216253e37646360">[email protected]</a>:a6d115bb1c0116036ac6e6e4d504665bc48879c421a450566c38b3b726f0a123
|
||
|
||
Port: <none>
|
||
|
||
Host Port: <none>
|
||
|
||
Command:
|
||
|
||
kube-controller-manager
|
||
|
||
--address=127.0.0.1
|
||
|
||
--cluster-signing-cert-file=/etc/kubernetes/pki/ca.crt
|
||
|
||
--cluster-signing-key-file=/etc/kubernetes/pki/ca.key
|
||
|
||
--controllers=*,bootstrapsigner,tokencleaner
|
||
|
||
--kubeconfig=/etc/kubernetes/controller-manager.conf
|
||
|
||
--leader-elect=true
|
||
|
||
--root-ca-file=/etc/kubernetes/pki/ca.crt
|
||
|
||
--service-account-private-key-file=/etc/kubernetes/pki/sa.key
|
||
|
||
--use-service-account-credentials=true
|
||
|
||
State: Running
|
||
|
||
Started: Mon, 10 Dec 2018 07:14:24 +0000
|
||
|
||
Ready: True
|
||
|
||
Restart Count: 0
|
||
|
||
Requests:
|
||
|
||
cpu: 200m
|
||
|
||
Liveness: http-get http://127.0.0.1:10252/healthz delay=15s timeout=15s period=10s #success=1 #failure=8
|
||
|
||
Environment: <none>
|
||
|
||
Mounts:
|
||
|
||
/etc/ca-certificates from etc-ca-certificates (ro)
|
||
|
||
/etc/kubernetes/controller-manager.conf from kubeconfig (ro)
|
||
|
||
/etc/kubernetes/pki from k8s-certs (ro)
|
||
|
||
/etc/ssl/certs from ca-certs (ro)
|
||
|
||
/usr/libexec/kubernetes/kubelet-plugins/volume/exec from flexvolume-dir (rw)
|
||
|
||
/usr/local/share/ca-certificates from usr-local-share-ca-certificates (ro)
|
||
|
||
/usr/share/ca-certificates from usr-share-ca-certificates (ro)
|
||
|
||
Conditions:
|
||
|
||
Type Status
|
||
|
||
Initialized True
|
||
|
||
Ready True
|
||
|
||
ContainersReady True
|
||
|
||
PodScheduled True
|
||
|
||
Volumes:
|
||
|
||
usr-share-ca-certificates:
|
||
|
||
Type: HostPath (bare host directory volume)
|
||
|
||
Path: /usr/share/ca-certificates
|
||
|
||
HostPathType: DirectoryOrCreate
|
||
|
||
usr-local-share-ca-certificates:
|
||
|
||
Type: HostPath (bare host directory volume)
|
||
|
||
Path: /usr/local/share/ca-certificates
|
||
|
||
HostPathType: DirectoryOrCreate
|
||
|
||
etc-ca-certificates:
|
||
|
||
Type: HostPath (bare host directory volume)
|
||
|
||
Path: /etc/ca-certificates
|
||
|
||
HostPathType: DirectoryOrCreate
|
||
|
||
k8s-certs:
|
||
|
||
Type: HostPath (bare host directory volume)
|
||
|
||
Path: /etc/kubernetes/pki
|
||
|
||
HostPathType: DirectoryOrCreate
|
||
|
||
ca-certs:
|
||
|
||
Type: HostPath (bare host directory volume)
|
||
|
||
Path: /etc/ssl/certs
|
||
|
||
HostPathType: DirectoryOrCreate
|
||
|
||
kubeconfig:
|
||
|
||
Type: HostPath (bare host directory volume)
|
||
|
||
Path: /etc/kubernetes/controller-manager.conf
|
||
|
||
HostPathType: FileOrCreate
|
||
|
||
flexvolume-dir:
|
||
|
||
Type: HostPath (bare host directory volume)
|
||
|
||
Path: /usr/libexec/kubernetes/kubelet-plugins/volume/exec
|
||
|
||
HostPathType: DirectoryOrCreate
|
||
|
||
QoS Class: Burstable
|
||
|
||
Node-Selectors: <none>
|
||
|
||
Tolerations: :NoExecute
|
||
|
||
Events: <none>
|
||
|
||
master
|
||
|
||
</code></pre>
|
||
|
||
<p>这是使用 <code>kubeadm</code> 搭建的集群中的 <code>kube-controller-manager</code> 的 <code>Pod</code>，首先可以看到它所使用的镜像，其次可以看到它使用的一系列参数，最后它在 <code>10252</code> 端口提供了健康检查的接口。稍后我们再展开。</p>
|
||
|
||
<ul>
|
||
|
||
<li>控制循环：这里拆解为两部分： <strong>控制</strong> 和 <strong>循环</strong> ，它所控制的是集群的状态；至于循环它当然是会有个循环间隔的，这里有个参数可以进行控制。</li>
|
||
|
||
<li>守护进程：这个就不单独展开了。</li>
|
||
|
||
</ul>
|
||
|
||
<h2><code>kube-controller-manager</code> 有什么作用</h2>
|
||
|
||
<p>前面已经说了它一个很关键的点 “控制”：它通过 <code>kube-apiserver</code> 提供的信息持续的监控集群状态，并尝试将集群调整至预期的状态。由于访问 <code>kube-apiserver</code> 也需要通过认证，授权等过程，所以可以看到上面启动 <code>kube-controller-manager</code> 时提供了一系列的参数。</p>
|
||
|
||
<p>比如，当我们创建了一个 <code>Deployment</code>，默认副本数为 1 ，当我们把 <code>Pod</code> 删除后，<code>kube-controller-manager</code> 会按照原先的预期，重新创建一个 <code>Pod</code> 。下面举个例子：</p>
|
||
|
||
<pre><code>master $ kubectl run redis --image='redis'
|
||
|
||
deployment.apps/redis created
|
||
|
||
master $ kubectl get all
|
||
|
||
NAME READY STATUS RESTARTS AGE
|
||
|
||
pod/redis-bb7894d65-w2rsp 1/1 Running 0 3m
|
||
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
|
||
|
||
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 18m
|
||
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
|
||
|
||
deployment.apps/redis 1 1 1 1 3m
|
||
NAME DESIRED CURRENT READY AGE
|
||
|
||
replicaset.apps/redis-bb7894d65 1 1 1 3m
|
||
|
||
master $ kubectl delete pod/redis-bb7894d65-w2rsp
|
||
|
||
pod "redis-bb7894d65-w2rsp" deleted
|
||
|
||
master $ kubectl get all # 可以看到已经重新运行了一个 Pod
|
||
|
||
NAME READY STATUS RESTARTS AGE
|
||
|
||
pod/redis-bb7894d65-62ftk 1/1 Running 0 16s
|
||
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
|
||
|
||
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 19m
|
||
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
|
||
|
||
deployment.apps/redis 1 1 1 1 4m
|
||
NAME DESIRED CURRENT READY AGE
|
||
|
||
replicaset.apps/redis-bb7894d65 1 1 1 4m
|
||
|
||
</code></pre>
|
||
|
||
<p>我们来看下 <code>kube-controller-manager</code> 的日志：</p>
|
||
|
||
<pre><code>master $ kubectl -n kube-system logs -l component=kube-controller-manager --tail=5
|
||
|
||
I1210 09:30:17.125377 1 node_lifecycle_controller.go:945] Controller detected that all Nodes are not-Ready. Entering master disruption mode.
|
||
|
||
I1210 09:31:07.140539 1 node_lifecycle_controller.go:972] Controller detected that some Nodes are Ready. Exiting master disruption mode.
|
||
|
||
I1210 09:43:30.377649 1 event.go:221] Event(v1.ObjectReference{Kind:"Deployment", Namespace:"default", Name:"redis", UID:"0d1cb2d7-fc60-11e8-a361-0242ac110074", APIVersion:"apps/v1", ResourceVersion:"1494", FieldPath:""}): type: 'Normal' reason: 'ScalingReplicaSet' Scaled up replica setredis-bb7894d65 to 1
|
||
|
||
I1210 09:43:30.835149 1 event.go:221] Event(v1.ObjectReference{Kind:"ReplicaSet", Namespace:"default", Name:"redis-bb7894d65", UID:"0d344d15-fc60-11e8-a361-0242ac110074", APIVersion:"apps/v1", ResourceVersion:"1495", FieldPath:""}): type: 'Normal' reason: 'SuccessfulCreate' Created pod:redis-bb7894d65-w2rsp
|
||
|
||
I1210 09:47:41.658781 1 event.go:221] Event(v1.ObjectReference{Kind:"ReplicaSet", Namespace:"default", Name:"redis-bb7894d65", UID:"0d344d15-fc60-11e8-a361-0242ac110074", APIVersion:"apps/v1", ResourceVersion:"1558", FieldPath:""}): type: 'Normal' reason: 'SuccessfulCreate' Created pod:redis-bb7894d65-62ftk
|
||
|
||
</code></pre>
|
||
|
||
<p>可以看到它先观察到有 <code>Deployment</code> 的事件，然后 <code>ScalingReplicaSet</code> 进而创建了对应的 <code>Pod</code>。 而当我们删掉正在运行的 <code>Pod</code> 后，它便会重新创建 <code>Pod</code> 使集群状态符合原先的预期状态。</p>
|
||
|
||
<p>同时，注意 <code>Pod</code> 的名字已经发生了变化。</p>
|
||
|
||
<h2><code>kube-controller-manager</code> 是如何工作的</h2>
|
||
|
||
<p>在 <code>cmd/kube-controller-manager/app/controllermanager.go</code> 中列出了大多数的 <code>controllermanager</code>，他们对 <code>controllermanager</code> 函数的实际调用都在 <code>cmd/kube-controller-manager/app/core.go</code> 中，我们以 <code>PodGC</code> 为例：</p>
|
||
|
||
<pre><code>func startPodGCController(ctx ControllerContext) (bool, error) {
|
||
|
||
go podgc.NewPodGC(
|
||
|
||
ctx.ClientBuilder.ClientOrDie("pod-garbage-collector"),
|
||
|
||
ctx.InformerFactory.Core().V1().Pods(),
|
||
|
||
int(ctx.ComponentConfig.PodGCController.TerminatedPodGCThreshold),
|
||
|
||
).Run(ctx.Stop)
|
||
|
||
return true, nil
|
||
|
||
}
|
||
|
||
</code></pre>
|
||
|
||
<p>在前两节中我们已经对 <code>kube-apiserver</code> 和 <code>etcd</code> 有了一些基本的认识，这里它主要会去 watch 相关的资源，但是出于性能上的考虑，也不能过于频繁的去请求 <code>kube-apiserver</code> 或者永久 watch ，所以在实现上借助了 <a href="https://github.com/kubernetes/client-go">client-go</a> 的 <code>informer</code> 包，相当于是实现了一个本地的二级缓存。这里不做过多展开。</p>
|
||
|
||
<p>它最终会调用 <code>PodGC</code> 的具体实现，位置在 <code>pkg/controller/podgc/gc_controller.go</code> 中：</p>
|
||
|
||
<pre><code>func NewPodGC(kubeClient clientset.Interface, podInformer coreinformers.PodInformer, terminatedPodThreshold int) *PodGCController {
|
||
|
||
if kubeClient != nil && kubeClient.CoreV1().RESTClient().GetRateLimiter() != nil {
|
||
|
||
metrics.RegisterMetricAndTrackRateLimiterUsage("gc_controller", kubeClient.CoreV1().RESTClient().GetRateLimiter())
|
||
|
||
}
|
||
|
||
gcc := &PodGCController{
|
||
|
||
kubeClient: kubeClient,
|
||
|
||
terminatedPodThreshold: terminatedPodThreshold,
|
||
|
||
deletePod: func(namespace, name string) error {
|
||
|
||
glog.Infof("PodGC is force deleting Pod: %v:%v", namespace, name)
|
||
|
||
return kubeClient.CoreV1().Pods(namespace).Delete(name, metav1.NewDeleteOptions(0))
|
||
|
||
},
|
||
|
||
}
|
||
gcc.podLister = podInformer.Lister()
|
||
|
||
gcc.podListerSynced = podInformer.Informer().HasSynced
|
||
return gcc
|
||
|
||
}
|
||
|
||
</code></pre>
|
||
|
||
<p>代码也比较直观，不过这里可以看到有一个注册 <code>metrics</code> 的过程，实际上 <code>kube-controller-manager</code> 在前面的 <code>10252</code> 端口上不仅暴露出来了一个 <code>/healthz</code> 接口，还暴露出了一个 <code>/metrics</code> 的接口，可用于进行监控之类的。</p>
|
||
|
||
<pre><code>master $ kubectl -n kube-system get pod -l component=kube-controller-manager
|
||
|
||
NAME READY STATUS RESTARTS AGE
|
||
|
||
kube-controller-manager-master 1/1 Running 1 2m
|
||
|
||
master $ kubectl -n kube-system exec -it kube-controller-manager-master sh
|
||
|
||
/ # wget -qO- http://127.0.0.1:10252/metrics|grep gc_controller
|
||
|
||
# HELP gc_controller_rate_limiter_use A metric measuring the saturation of the rate limiter for gc_controller
|
||
|
||
# TYPE gc_controller_rate_limiter_use gauge
|
||
|
||
gc_controller_rate_limiter_use 0
|
||
|
||
</code></pre>
|
||
|
||
<h2>总结</h2>
|
||
|
||
<p>在本节中，我们介绍了 <code>kube-controller-manager</code> 以及它在 K8S 中主要是将集群调节至预期的状态，并提供出了 <code>/metrics</code> 的接口可供监控。</p>
|
||
|
||
<p><code>kube-controller-manager</code> 中有很多的 controller 大多数是默认开启的，当然也有默认关闭的，比如 <code>bootstrapsigner</code> 和 <code>tokencleaner</code>，在我们启动 <code>kube-controller-manager</code> 的时候，可通过 <code>--controllers</code> 的参数进行控制，就比如上面例子中 <code>--controllers=*,bootstrapsigner,tokencleaner</code> 表示开启所有默认开启的以及 <code>bootstrapsigner</code> 和 <code>tokencleaner</code> 。</p>
|
||
|
||
<p>下节，我们将学习另一个与资源调度有关的组件 <code>kube-scheduler</code>，了解下它对我们使用集群所带来的意义。</p>
|
||
|
||
</div>
|
||
|
||
</div>
|
||
|
||
<div>
|
||
|
||
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|
||
|
||
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