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<div><h1>16 庖丁解牛：kubelet</h1>
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<h2>整体概览</h2>
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<pre><code>+--------------------------------------------------------+
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| +---------------------+ +---------------------+ |
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| | kubelet | | kube-proxy | |
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| | | | | |
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| +---------------------+ +---------------------+ |
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| +----------------------------------------------------+ |
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| | Container Runtime (Docker) | |
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| | +---------------------+ +---------------------+ | |
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| | |Pod | |Pod | | |
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| | | +-----+ +-----+ | |+-----++-----++-----+| | |
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| | | |C1 | |C2 | | ||C1 ||C2 ||C3 || | |
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| | | | | | | | || || || || | |
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| | | +-----+ +-----+ | |+-----++-----++-----+| | |
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| | +---------------------+ +---------------------+ | |
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| +----------------------------------------------------+ |
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+--------------------------------------------------------+
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</code></pre>
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<p>在第 3 节《宏观认识：整体架构》 中，我们知道了 K8S 中 Node 由一些必要的组件构成，而其中最为核心的当属 <code>kubelet</code> 了，如果没有 <code>kubelet</code> 的存在，那我们预期的各类资源就只能存在于 <code>Master</code> 的相关组件中了，而 K8S 也很能只是一个 CRUD 的普通程序了。本节，我们来介绍下 <code>kubelet</code> 及它是如何完成这一系列任务的。</p>
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<h2><code>kubelet</code> 是什么</h2>
|
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<p>按照一般架构设计上的习惯，<code>kubelet</code> 所承担的角色一般会被叫做 <code>agent</code>，这里叫做 <code>kubelet</code> 很大程度上受 <code>Borg</code> 的命名影响，<code>Borg</code> 里面也有一个 <code>Borglet</code> 的组件存在。<code>kubelet</code> 便是 K8S 中的 <code>agent</code>，负责 <code>Node</code> 和 <code>Pod</code> 相关的管理任务。</p>
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<p>同样的，在我们下载 K8S 二进制文件解压后，便可以得到 <code>kubelet</code> 的可执行文件。在第 5 节中，我们也完成了 <code>kubelet</code> 以 <code>systemd</code> 进行启动和管理的相关配置。</p>
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<h2><code>kubelet</code> 有什么作用</h2>
|
||
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<p>通常来讲 <code>agent</code> 这样的角色起到的作用首先便是要能够注册，让 <code>server</code> 端知道它的存在，所以这便是它的第一个作用：节点管理。</p>
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<h3>节点管理</h3>
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<p>当我们执行 <code>kubelet --help</code> 的时候，会看到它所支持的可配置参数，其中有一个 <code>--register-node</code> 参数便是用于控制是否向 <code>kube-apiserver</code> 注册节点的，默认是开启的。</p>
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<p>我们在第 5 节中还介绍了如何新增一个 <code>Node</code>，当 <code>kubeadm join</code> 执行成功后，你便可以通过 <code>kubectl get node</code> 查看到新加入集群中的 <code>Node</code>，与此同时，你也可以在该节点上通过以下命令查看 <code>kubelet</code> 的状态。</p>
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<pre><code>master $ systemctl status kubelet
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● kubelet.service - kubelet: The Kubernetes Agent
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Loaded: loaded (/etc/systemd/system/kubelet.service; enabled; vendor preset: disabled)
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||
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Drop-In: /etc/systemd/system/kubelet.service.d
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└─kubeadm.conf
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Active: active (running) since Thu 2018-12-13 07:49:51 UTC; 32min ago
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|
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Docs: http://kubernetes.io/docs/
|
||
|
||
Main PID: 3876259 (kubelet)
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||
|
||
Memory: 66.3M
|
||
|
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CGroup: /system.slice/kubelet.service
|
||
|
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└─3876259 /usr/bin/kubelet --bootstrap-kubeconfig=/etc/kubernetes/bootstrap-kubelet.conf --kubeconfig=/etc/kubernete...
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||
|
||
</code></pre>
|
||
|
||
<p>当我们查看 <code>Node</code> 信息时，也能得到如下输出：</p>
|
||
|
||
<pre><code>master $ kubectl get nodes node01 -o yaml
|
||
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||
apiVersion: v1
|
||
|
||
kind: Node
|
||
|
||
metadata:
|
||
|
||
annotations:
|
||
|
||
kubeadm.alpha.kubernetes.io/cri-socket: /var/run/dockershim.sock
|
||
|
||
node.alpha.kubernetes.io/ttl: "0"
|
||
|
||
volumes.kubernetes.io/controller-managed-attach-detach: "true"
|
||
|
||
creationTimestamp: 2018-12-13T07:50:47Z
|
||
|
||
labels:
|
||
|
||
beta.kubernetes.io/arch: amd64
|
||
|
||
beta.kubernetes.io/os: linux
|
||
|
||
kubernetes.io/hostname: node01
|
||
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||
name: node01
|
||
|
||
resourceVersion: "4242"
|
||
|
||
selfLink: /api/v1/nodes/node01
|
||
|
||
uid: cd612df6-feab-11e8-9a0b-0242ac110096
|
||
|
||
spec: {}
|
||
|
||
status:
|
||
|
||
addresses:
|
||
|
||
- address: 172.17.0.152
|
||
|
||
type: InternalIP
|
||
|
||
- address: node01
|
||
|
||
type: Hostname
|
||
|
||
allocatable:
|
||
|
||
cpu: "4"
|
||
|
||
ephemeral-storage: "89032026784"
|
||
|
||
hugepages-1Gi: "0"
|
||
|
||
hugepages-2Mi: "0"
|
||
|
||
memory: 3894788Ki
|
||
|
||
pods: "110"
|
||
|
||
capacity:
|
||
|
||
cpu: "4"
|
||
|
||
ephemeral-storage: 96605932Ki
|
||
|
||
hugepages-1Gi: "0"
|
||
|
||
hugepages-2Mi: "0"
|
||
|
||
memory: 3997188Ki
|
||
|
||
pods: "110"
|
||
|
||
conditions:
|
||
|
||
- lastHeartbeatTime: 2018-12-13T08:39:41Z
|
||
|
||
lastTransitionTime: 2018-12-13T07:50:47Z
|
||
|
||
message: kubelet has sufficient disk space available
|
||
|
||
reason: KubeletHasSufficientDisk
|
||
|
||
status: "False"
|
||
|
||
type: OutOfDisk
|
||
|
||
- lastHeartbeatTime: 2018-12-13T08:39:41Z
|
||
|
||
lastTransitionTime: 2018-12-13T07:50:47Z
|
||
|
||
message: kubelet has sufficient memory available
|
||
|
||
reason: KubeletHasSufficientMemory
|
||
|
||
status: "False"
|
||
|
||
type: MemoryPressure
|
||
|
||
- lastHeartbeatTime: 2018-12-13T08:39:41Z
|
||
|
||
lastTransitionTime: 2018-12-13T07:50:47Z
|
||
|
||
message: kubelet has no disk pressure
|
||
|
||
reason: KubeletHasNoDiskPressure
|
||
|
||
status: "False"
|
||
|
||
type: DiskPressure
|
||
|
||
- lastHeartbeatTime: 2018-12-13T08:39:41Z
|
||
|
||
lastTransitionTime: 2018-12-13T07:50:47Z
|
||
|
||
message: kubelet has sufficient PID available
|
||
|
||
reason: KubeletHasSufficientPID
|
||
|
||
status: "False"
|
||
|
||
type: PIDPressure
|
||
|
||
- lastHeartbeatTime: 2018-12-13T08:39:41Z
|
||
|
||
lastTransitionTime: 2018-12-13T07:51:37Z
|
||
|
||
message: kubelet is posting ready status. AppArmor enabled
|
||
|
||
reason: KubeletReady
|
||
|
||
status: "True"
|
||
|
||
type: Ready
|
||
|
||
daemonEndpoints:
|
||
|
||
kubeletEndpoint:
|
||
|
||
Port: 10250
|
||
|
||
images:
|
||
|
||
- names:
|
||
|
||
- k8s.gcr.io/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="0b607e696e266a7b62786e797d6e79266a666f3d3f4b78636a393e3d">[email protected]</a>:956bea8c139620c9fc823fb81ff9b5647582b53bd33904302987d56ab24fc187
|
||
|
||
- k8s.gcr.io/kube-apiserver-amd64:v1.11.3
|
||
|
||
sizeBytes: 186676561
|
||
|
||
nodeInfo:
|
||
|
||
architecture: amd64
|
||
|
||
bootID: 89ced22c-f7f8-4c4d-ad0d-d10887ab900e
|
||
|
||
containerRuntimeVersion: docker://18.6.0
|
||
|
||
kernelVersion: 4.4.0-62-generic
|
||
|
||
kubeProxyVersion: v1.11.3
|
||
|
||
kubeletVersion: v1.11.3
|
||
|
||
machineID: 26ba042302eea8095d6576975c120eeb
|
||
|
||
operatingSystem: linux
|
||
|
||
osImage: Ubuntu 16.04.2 LTS
|
||
|
||
systemUUID: 26ba042302eea8095d6576975c120eeb
|
||
|
||
</code></pre>
|
||
|
||
<p>可以看到 <code>kubelet</code> 不仅将自己注册给了 <code>kube-apiserver</code>，同时它所在机器的信息也都进行了上报，包括 CPU，内存，IP 信息等。</p>
|
||
|
||
<p>这其中有我们在第 2 节中提到的关于 <code>Node</code> 状态相关的一些信息，可以对照着看看。</p>
|
||
|
||
<p>当然这里除了这些信息外，还有些值得注意的，比如 <code>daemonEndpoints</code> 之类的，可以看到目前 <code>kubelet</code> 监听在了 <code>10250</code> 端口，这个端口可通过 <code>--port</code> 配置，但是之后会被废弃掉，我们是写入了 <code>/var/lib/kubelet/config.yaml</code> 的配置文件中。</p>
|
||
|
||
<pre><code>master $ cat /var/lib/kubelet/config.yaml
|
||
|
||
address: 0.0.0.0
|
||
|
||
apiVersion: kubelet.config.k8s.io/v1beta1
|
||
|
||
authentication:
|
||
|
||
anonymous:
|
||
|
||
enabled: false
|
||
|
||
webhook:
|
||
|
||
cacheTTL: 2m0s
|
||
|
||
enabled: true
|
||
|
||
x509:
|
||
|
||
clientCAFile: /etc/kubernetes/pki/ca.crt
|
||
|
||
authorization:
|
||
|
||
mode: Webhook
|
||
|
||
webhook:
|
||
|
||
cacheAuthorizedTTL: 5m0s
|
||
|
||
cacheUnauthorizedTTL: 30s
|
||
|
||
cgroupDriver: cgroupfs
|
||
|
||
cgroupsPerQOS: true
|
||
|
||
clusterDNS:
|
||
|
||
- 10.96.0.10
|
||
|
||
clusterDomain: cluster.local
|
||
|
||
containerLogMaxFiles: 5
|
||
|
||
containerLogMaxSize: 10Mi
|
||
|
||
contentType: application/vnd.kubernetes.protobuf
|
||
|
||
cpuCFSQuota: true
|
||
|
||
cpuManagerPolicy: none
|
||
|
||
cpuManagerReconcilePeriod: 10s
|
||
|
||
enableControllerAttachDetach: true
|
||
|
||
enableDebuggingHandlers: true
|
||
|
||
enforceNodeAllocatable:
|
||
|
||
- pods
|
||
|
||
eventBurst: 10
|
||
|
||
eventRecordQPS: 5
|
||
|
||
evictionHard:
|
||
|
||
imagefs.available: 15%
|
||
|
||
memory.available: 100Mi
|
||
|
||
nodefs.available: 10%
|
||
|
||
nodefs.inodesFree: 5%
|
||
|
||
evictionPressureTransitionPeriod: 5m0s
|
||
|
||
failSwapOn: true
|
||
|
||
fileCheckFrequency: 20s
|
||
|
||
hairpinMode: promiscuous-bridge
|
||
|
||
healthzBindAddress: 127.0.0.1
|
||
|
||
healthzPort: 10248
|
||
|
||
httpCheckFrequency: 20s
|
||
|
||
imageGCHighThresholdPercent: 85
|
||
|
||
imageGCLowThresholdPercent: 80
|
||
|
||
imageMinimumGCAge: 2m0s
|
||
|
||
iptablesDropBit: 15
|
||
|
||
iptablesMasqueradeBit: 14
|
||
|
||
kind: KubeletConfiguration
|
||
|
||
kubeAPIBurst: 10
|
||
|
||
kubeAPIQPS: 5
|
||
|
||
makeIPTablesUtilChains: true
|
||
|
||
maxOpenFiles: 1000000
|
||
|
||
maxPods: 110
|
||
|
||
nodeStatusUpdateFrequency: 10s
|
||
|
||
oomScoreAdj: -999
|
||
|
||
podPidsLimit: -1
|
||
|
||
port: 10250
|
||
|
||
registryBurst: 10
|
||
|
||
registryPullQPS: 5
|
||
|
||
resolvConf: /etc/resolv.conf
|
||
|
||
rotateCertificates: true
|
||
|
||
runtimeRequestTimeout: 2m0s
|
||
|
||
serializeImagePulls: true
|
||
|
||
staticPodPath: /etc/kubernetes/manifests
|
||
|
||
streamingConnectionIdleTimeout: 4h0m0s
|
||
|
||
syncFrequency: 1m0s
|
||
|
||
volumeStatsAggPeriod: 1m0s
|
||
|
||
master $
|
||
|
||
</code></pre>
|
||
|
||
<p>这其中有一些需要关注的配置：</p>
|
||
|
||
<ul>
|
||
|
||
<li>
|
||
|
||
<p><code>maxPods</code>：最大的 <code>Pod</code> 数</p>
|
||
|
||
</li>
|
||
|
||
<li>
|
||
|
||
<p><code>healthzBindAddress</code> 和 <code>healthzPort</code>：配置了健康检查所监听的地址和端口</p>
|
||
|
||
<p>我们可用以下方式进行验证：</p>
|
||
|
||
<pre><code>master $ curl 127.0.0.1:10248/healthz
|
||
|
||
ok
|
||
|
||
</code></pre>
|
||
|
||
</li>
|
||
|
||
<li>
|
||
|
||
<p><code>authentication</code> 和 <code>authorization</code> ：认证授权相关</p>
|
||
|
||
</li>
|
||
|
||
<li>
|
||
|
||
<p><code>evictionHard</code>：涉及到 <code>kubelet</code> 的驱逐策略，对 <code>Pod</code> 调度分配之类的影响很大</p>
|
||
|
||
</li>
|
||
|
||
</ul>
|
||
|
||
<p>其余部分，可参考<a href="https://kubernetes.io/docs/tasks/administer-cluster/out-of-resource/">手册内容</a></p>
|
||
|
||
<h3>Pod 管理</h3>
|
||
|
||
<p>从上面的配置以及我们之前的介绍中，<code>kube-scheduler</code> 处理了 <code>Pod</code> 应该调度至哪个 <code>Node</code>，而 <code>kubelet</code> 则是保障该 <code>Pod</code> 能按照预期，在对应 <code>Node</code> 上启动并保持工作。</p>
|
||
|
||
<p>同时，<code>kubelet</code> 在保障 <code>Pod</code> 能按预期工作，主要是做了两方面的事情：</p>
|
||
|
||
<ul>
|
||
|
||
<li>健康检查：通过 <code>LivenessProbe</code> 和 <code>ReadinessProbe</code> 探针进行检查，判断是否健康及是否已经准备好接受请求。</li>
|
||
|
||
<li>资源监控：通过 <code>cAdvisor</code> 进行资源监。</li>
|
||
|
||
</ul>
|
||
|
||
<h2><code>kubelet</code> 是如何工作的</h2>
|
||
|
||
<p>大致的功能已经介绍了，我们来看下它大体的实现。</p>
|
||
|
||
<p>首先是在 <code>cmd/kubelet/app/server.go</code> 文件中的 <code>Run</code> 方法：</p>
|
||
|
||
<pre><code>func Run(s *options.KubeletServer, kubeDeps *kubelet.Dependencies, stopCh <-chan struct{}) error {
|
||
|
||
glog.Infof("Version: %+v", version.Get())
|
||
|
||
if err := initForOS(s.KubeletFlags.WindowsService); err != nil {
|
||
|
||
return fmt.Errorf("failed OS init: %v", err)
|
||
|
||
}
|
||
|
||
if err := run(s, kubeDeps, stopCh); err != nil {
|
||
|
||
return fmt.Errorf("failed to run Kubelet: %v", err)
|
||
|
||
}
|
||
|
||
return nil
|
||
|
||
}
|
||
|
||
</code></pre>
|
||
|
||
<p>这个方法看起来很简单那，它是在读取完一系列的配置和校验之后开始被调用的，在调用过程中，会在日志中输出当前的版本号，如果你的 <code>kubelet</code> 已经正常运行，当你执行 <code>journalctl -u kubelet</code> 的时候，便会看到一条相关的日志输出。</p>
|
||
|
||
<p>之后，便是一个 <code>run</code> 方法，其中包含着各种环境检查，容器管理，<code>cAdvisor</code> 初始化之类的操作，直到 <code>kubelet</code> 基本正确运行后，则会调用 <code>pkg/kubelet/kubelet.go</code> 中的一个 <code>BirthCry</code> 方法，该方法从命名就可以看出来，它其实就是宣告 <code>kubelet</code> 已经启动：</p>
|
||
|
||
<pre><code>func (kl *Kubelet) BirthCry() {
|
||
|
||
kl.recorder.Eventf(kl.nodeRef, v1.EventTypeNormal, events.StartingKubelet, "Starting kubelet.")
|
||
|
||
}
|
||
|
||
</code></pre>
|
||
|
||
<p>后续则是关于注册，<code>Pod</code> 管理以及资源相关的处理逻辑，内容较多，这里就不再展开了。</p>
|
||
|
||
<h2>总结</h2>
|
||
|
||
<p>本节中我们介绍了 <code>kubelet</code> 的主要功能和基本实现，了解到了它不仅可将自身注册到集群，同时还承担着保障 <code>Pod</code> 可在该 <code>Node</code> 上按预期工作。另外 <code>kubelet</code> 其实还承担着清理 <code>Node</code> 上一些由 K8S 调度 <code>Pod</code> 所造成的磁盘占用之类的工作。</p>
|
||
|
||
<p>从上面的配置中基本能看出来一些，这部分的功能大多数情况下不需要大家人为干预，所以也就不再展开了。</p>
|
||
|
||
<p>当 <code>Pod</code> 在 <code>Node</code> 上正常运行之后，若是需要对外提供服务，则需要将其暴露出来。下节，我们来介绍下 <code>kube-proxy</code> 是如何来处理这些工作的。</p>
|
||
|
||
</div>
|
||
|
||
</div>
|
||
|
||
<div>
|
||
|
||
<div style="float: left">
|
||
|
||
<a href="/专栏/Kubernetes 从上手到实践/15 庖丁解牛：kube-scheduler.md.html">上一页</a>
|
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|
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</div>
|
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|
||
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|
||
|
||
<a href="/专栏/Kubernetes 从上手到实践/17 庖丁解牛：kube-proxy.md.html">下一页</a>
|
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|
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