1. k8s之client-go源码剖析

Face with a smile, not to complain.

Client-Go源码结构

源码结构: client-go

1.1 Client-Go之五大客户端对象

client-go 是一个调用Kubernetes集群资源对象API的客户端，通过Client-go实现对Kubernetes集群中资源对象(Deploment,Service,Pod,Secret等)的CRUD操作。官方文档：https://github.com/kubernetes/client-go

1.1.1 基础常识 client-go 操作k8s集群其实是通过kubeconfig配置信息或者k8s-api-server的地址连接指定的kubernetes-api-server，连接k8s例子：

1.获取依赖包

go get github.com/kubernetes/client-go

2.连接k8s(确保本地有kubeconfig配置文件)

package main

import (
    "flag"
    "fmt"
    "os"
    "path/filepath"
    "time"

    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/tools/clientcmd"
)
func main() {
  var kubeconfig *string
  if home := homeDir(); home != "" {
        kubeconfig = flag.String("kubeconfig", filepath.Join(home, ".kube", "config"), "(optional) absolute path to the kubeconfig file")
    } else {
        kubeconfig = flag.String("kubeconfig", "", "absolute path to the kubeconfig file")
    }
  flag.Parse()
  // uses the current context in kubeconfig
  config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
  if err != nil {
      panic(err.Error())
  }
  // creates the clientset
  clientset, err := kubernetes.NewForConfig(config)
  if err != nil {
      panic(err.Error())
  }
  // get pods list
  for {
      pods, err := clientset.CoreV1().Pods("").List(metav1.ListOptions{})
      if err != nil {
          panic(err.Error())
      }
      fmt.Printf("There are %d pods in the cluster\n", len(pods.Items))
      time.Sleep(10 * time.Second)
  }
}

func homeDir() string {
  if h := os.Getenv("HOME"); h != "" {
    return h
  }
  return os.Getenv("USERPROFILE") // windows
}

1.1.2 RESTClient RESTClient是最基础的客户端，它是基于对Http Request进行了封装，实现RESTful风格的API，其他Client都是基于RESTClient实现的,实际上就是一个http client 通过参数(master的url或者kubeconfig路径)和BuildConfigFronFlags
```
 // config      
  config,err := clientcmd.BuildConfigFormFlags("masterURL",*kubeconfig)
  // restClient
  restClient,err := rest.RESTClientFor(config)
```

源码路径：k8s.io/client-go/rest/client.go

// RESTClient imposes common Kubernetes API conventions on a set of resource paths.
// The baseURL is expected to point to an HTTP or HTTPS path that is the parent
// of one or more resources.  The server should return a decodable API resource
// object, or an api.Status object which contains information about the reason for
// any failure.
//
// Most consumers should use client.New() to get a Kubernetes API client.
type RESTClient struct {
    // base is the root URL for all invocations of the client
    base *url.URL
    // versionedAPIPath is a path segment connecting the base URL to the resource root
    versionedAPIPath string

    // contentConfig is the information used to communicate with the server.
    contentConfig ContentConfig

    // serializers contain all serializers for underlying content type.
    serializers Serializers

    // creates BackoffManager that is passed to requests.
    createBackoffMgr func() BackoffManager

    // TODO extract this into a wrapper interface via the RESTClient interface in kubectl.
    Throttle flowcontrol.RateLimiter

    // Set specific behavior of the client.  If not set http.DefaultClient will be used.
    Client *http.Client
}

源码路径：k8s.io/client-go/rest/client.go RESTClient.Interface中方法如下：

  // Interface captures the set of operations for generically interacting with Kubernetes REST apis.
  type Interface interface {
      GetRateLimiter() flowcontrol.RateLimiter
      Verb(verb string) *Request
      Post() *Request
      Put() *Request
      Patch(pt types.PatchType) *Request
      Get() *Request
      Delete() *Request
      APIVersion() schema.GroupVersion
  }

Discovery Client discovery client(发现客户端)，用于发现kube-apiserver支持的资源组、资源版本以及资源信息等(即Versions,Groups,Resources)

// config      
config,err := clientcmd.BuildConfigFormFlags("masterURL",*kubeconfig)
// discovery client
discoveryClient, err := discovery.NewDiscoveryClientForConfig(config)

1.1.3 Dynamic Client dynamic client能够处理kubernetes集群中的所有资源对象，包括用户自定义资源

// config      
config,err := clientcmd.BuildConfigFormFlags("masterURL",*kubeconfig)
// dynamic client
dynamicClient, err := dynamic.NewForConfig(config)

1.1.4 ClientSet Client ClientSet是在RESTClient基础上封装的对k8s资源(Resoures)和版本(Versions)操作管理的客户端，只能够处理k8s内置资源(Pod，Namespace等)

// config      
config,err := clientcmd.BuildConfigFormFlags("masterURL",*kubeconfig)
// clientSet client
clientSet,err := kubernetes.NewForCofig(cofnig)
// get pods
pods, err := clientset.CoreV1().Pods("").List(metav1.ListOptions{})

clientset的结构体

  // Clientset contains the clients for groups. Each group has exactly one
  // version included in a Clientset.
  type Clientset struct {
      *discovery.DiscoveryClient
      admissionregistrationV1alpha1 *admissionregistrationv1alpha1.AdmissionregistrationV1alpha1Client
      appsV1beta1                   *appsv1beta1.AppsV1beta1Client
      appsV1beta2                   *appsv1beta2.AppsV1beta2Client
      authenticationV1              *authenticationv1.AuthenticationV1Client
      authenticationV1beta1         *authenticationv1beta1.AuthenticationV1beta1Client
      authorizationV1               *authorizationv1.AuthorizationV1Client
      authorizationV1beta1          *authorizationv1beta1.AuthorizationV1beta1Client
      autoscalingV1                 *autoscalingv1.AutoscalingV1Client
      autoscalingV2beta1            *autoscalingv2beta1.AutoscalingV2beta1Client
      batchV1                       *batchv1.BatchV1Client
      batchV1beta1                  *batchv1beta1.BatchV1beta1Client
      batchV2alpha1                 *batchv2alpha1.BatchV2alpha1Client
      certificatesV1beta1           *certificatesv1beta1.CertificatesV1beta1Client
      coreV1                        *corev1.CoreV1Client
      extensionsV1beta1             *extensionsv1beta1.ExtensionsV1beta1Client
      networkingV1                  *networkingv1.NetworkingV1Client
      policyV1beta1                 *policyv1beta1.PolicyV1beta1Client
      rbacV1                        *rbacv1.RbacV1Client
      rbacV1beta1                   *rbacv1beta1.RbacV1beta1Client
      rbacV1alpha1                  *rbacv1alpha1.RbacV1alpha1Client
      schedulingV1alpha1            *schedulingv1alpha1.SchedulingV1alpha1Client
      settingsV1alpha1              *settingsv1alpha1.SettingsV1alpha1Client
      storageV1beta1                *storagev1beta1.StorageV1beta1Client
      storageV1                     *storagev1.StorageV1Client
  }

1.2 Client-Go之Informer机制

Informer机制是保证kubernetes各个组件通过http协议通信消息的一致性、实时性、顺序性

1.2.1 Informer机制核心组件以及运行原理图

Informer核心组件：
Informer运行原理图：

图片来源：kubernetes源码剖析

informer-runtime

1.2.2

1.3 Clinet-Go之WorkQueue

1.4 Client-Go之事件管理器

1.5 k8s-dashboard对client-go的一些封装

1.6 Client-Go的基础操作

1.7 成长与思考

1.7.1 client-go总结

client-go主要功能就是对k8s集群的各种资源进行操作，针对每种资源都封装成了相应的client提供调用，使用client-go时首先需要获取kubernetes配置信息，即kubeconfig，大致目录：$HOME/.kube/config。

调用过程如下：

加载kubeconfig配置文件-> resr.config -> clientset -> 具体的client(CoreV1Client)->具体的资源对象(pod)->RESTClient->http.Client→HTTP请求的发送及响应

通过clientset中不同的client和client中不同资源对象的方法实现对kubernetes中资源对象的增删改查等操作，常用的client有CoreV1Client、AppsV1beta1Client、ExtensionsV1beta1Client等。

K8S源码剖析之Client-Go

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