client-go的四种客户端

client-go提供了四种与Kubernetes APIServer交互的客户端：RESTClient、DiscoveryClient、ClientSet、DynamicClient。经过学习之后，我感觉这个东西还是蛮不复杂的，以下是这四种客户端获取所有Pods的demo，然后感受一下他们的区别。

运行在下面的四个代码时，需要准备好kubeconfig，就是~/.kube/config这个文件，可以从服务器上拷到本地上。或者直接放在服务器上跑这些代码。

RESTClient

RESTClient是一个最基础的client，他是其他三种client的底层，也就是说，其他三种client都是封装的它。所以操作RESTClient会感觉比较原始。我们

go 复制代码

import (
    "context"
    "flag"
    "fmt"
    corev1 "k8s.io/api/core/v1"
    "k8s.io/client-go/kubernetes/scheme"
    "k8s.io/client-go/rest"
    "k8s.io/client-go/tools/clientcmd"
    "k8s.io/client-go/util/homedir"
    "path/filepath"
)

func main() {
    var kubeconfig *string
    if home := homedir.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()

    config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
    if err != nil {
       panic(err.Error())
    }

    config.APIPath = "api"
    // 设置 corev1 groupVersion
    config.GroupVersion = &corev1.SchemeGroupVersion
    // 设置解析器，用于用于解析 scheme
    config.NegotiatedSerializer = scheme.Codecs.WithoutConversion()
    // 初始化 RESTClient
    restClient, err := rest.RESTClientFor(config)
    if err != nil {
       panic(err)
    }
    list := &corev1.PodList{}
    // namespace为空，就返回所有namespace中的资源
    err = restClient.Get().Namespace("").Resource("pods").Do(context.TODO()).Into(list)
    if err != nil {
       panic(err)
    }

    for _, item := range list.Items {
       fmt.Printf("ns:%s , pod:%s\n", item.Namespace, item.Name)
    }
}

ClientSet

ClientSet他是用来操作K8s内置资源的，底层给每一种资源封了RESTClient，如果想操作CRD，需要自己定义ClientSet。

go 复制代码

func main() {
    var kubeconfig *string
    if home := homedir.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()

    // 从kubeconfig中获取配置
    config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
    if err != nil {
       panic(err.Error())
    }

    // 从配置中获得clientset
    clientset, err := kubernetes.NewForConfig(config)
    if err != nil {
       panic(err.Error())
    }
    pods, err := clientset.CoreV1().Pods("").List(context.TODO(), metav1.ListOptions{})
    if err != nil {
       panic(err.Error())
    }
    fmt.Printf("There are %d pods in the cluster\n", len(pods.Items))

    for _, item := range pods.Items {
       fmt.Printf("ns:%s , pod:%s\n", item.Namespace, item.Name)
    }
}

其实最后来时落到了这里，所以他是帮我们把一些操作封了一下。

go 复制代码

func (c *pods) List(ctx context.Context, opts metav1.ListOptions) (result *v1.PodList, err error) {
    var timeout time.Duration
    if opts.TimeoutSeconds != nil {
       timeout = time.Duration(*opts.TimeoutSeconds) * time.Second
    }
    result = &v1.PodList{}
    err = c.client.Get().
       Namespace(c.ns).
       Resource("pods").
       VersionedParams(&opts, scheme.ParameterCodec).
       Timeout(timeout).
       Do(ctx).
       Into(result)
    return
}

DynamicClient

动态client的就是比较动态，然后他可以操作CRD，但是他返回的内容是map

go 复制代码

func main() {
    var kubeconfig *string
    if home := homedir.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()

    // 从kubeconfig中获取配置
    config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
    if err != nil {
       panic(err.Error())
    }

    dynamicClient, err := dynamic.NewForConfig(config)
    if err != nil {
       panic(err.Error())
    }

    // 因为是动态调用，不需要操作哪个资源，所以需要自己提供
    gvr := schema.GroupVersionResource{
       Group:    "",
       Version:  "v1",
       Resource: "pods",
    }

    result, err := dynamicClient.Resource(gvr).Namespace("").List(context.TODO(), meta_v1.ListOptions{})
    podList := &corev1.PodList{}
    // 将结果解析到 podList scheme 中
    err = runtime.DefaultUnstructuredConverter.FromUnstructured(
       result.UnstructuredContent(), podList)

    for _, item := range podList.Items {
       fmt.Printf("ns: %s,pod: %s\n", item.Namespace, item.Name)
    }
}

我们这里把的结构化数据转为了结构化数据。

DiscoveryClient

发现客户端是用来用于发现 Kube-apiserver 支持的资源组、资源版本、资源类型等。通过DiscoveryClient发现所有gvr

go 复制代码

func main() {
    var kubeconfig *string
    if home := homedir.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()

    // 从kubeconfig中获取配置
    config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
    if err != nil {
       panic(err.Error())
    }

    // 初始化 DiscoveryClient
    discoveryClient, err := discovery.NewDiscoveryClientForConfig(config)
    if err != nil {
       panic(err.Error())
    }
    // 获取集群所有资源
    _, apiResourceList, err := discoveryClient.ServerGroupsAndResources()
    if err != nil {
       panic(err.Error())
    }

    for _, resources := range apiResourceList {
       gv, err := schema.ParseGroupVersion(resources.GroupVersion)
       if err != nil {
          panic(err.Error())
       }
       for _, resource := range resources.APIResources {
          fmt.Printf("group: %s, version: %s, resource: %s\n", gv.Group, gv.Version, resource.Name)
       }

    }
}