01-client-go
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1、介绍
client-go 是用来和 k8s 集群交互的go语言客户端库，地址为：https://github.com/kubernetes/client-go client-go 的版本有两种标识方式：
- v0.x.y (For each
v1.x.yKubernetes release, the major version (first digit) would remain0) - kubernetes-1.x.y
ps: k8s 发布v1.30.0 版本时，client-go 会同步发布两个版本 v0.30.0 (推荐使用)和 kubernetes-1.30.0
如果你想使用最新版本的客户端库，你可以运行如下命令：
go get k8s.io/client-go@latest
如果你想使用特定版本，推荐使用如下命令：
go get k8s.io/client-go@v0.20.4
2、目录结构
client-go 包含以下几部分：
- The
kubernetespackage contains the clientset to access Kubernetes API. - The
discoverypackage is used to discover APIs supported by a Kubernetes API server. - The
dynamicpackage contains a dynamic client that can perform generic operations on arbitrary Kubernetes API objects. - The
plugin/pkg/client/authpackages contain optional authentication plugins for obtaining credentials from external sources. - The
transportpackage is used to set up auth and start a connection. - The
tools/cachepackage is useful for writing controllers.
3、使用
1.初始化
- 集群内初始化
- 集群外初始化
如果你的应用跑在集群中的pod上，推荐使用集群内初始化，否则使用集群外初始化。
// 集群外初始化 client
// 需要集群的 kubeconfig 配置文件
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()
// use the current context in kubeconfig
config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
if err != nil {
panic(err.Error())
}
// create the clientset
clientset, err := kubernetes.NewForConfig(config)
if err != nil {
panic(err.Error())
}
}
2. 列出集群内pod资源
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))
上述代码在client-
go仓库下examples目录
你可以运行该代码：
cd out-of-cluster-client-configuration
go build -o app .
./app -kubeconfig=/path/to/xxx
3. deployment资源CRUD - typed (clientset)方式
以下代码创建一个有2个副本数的deployment，然后更新副本数为1，升级nginx镜像版本，最后删除
deploymentsClient := clientset.AppsV1().Deployments(apiv1.NamespaceDefault)
deployment := &appsv1.Deployment{
ObjectMeta: metav1.ObjectMeta{
Name: "demo-deployment",
},
Spec: appsv1.DeploymentSpec{
Replicas: int32Ptr(2),
Selector: &metav1.LabelSelector{
MatchLabels: map[string]string{
"app": "demo",
},
},
Template: apiv1.PodTemplateSpec{
ObjectMeta: metav1.ObjectMeta{
Labels: map[string]string{
"app": "demo",
},
},
Spec: apiv1.PodSpec{
Containers: []apiv1.Container{
{
Name: "web",
Image: "nginx:1.12",
Ports: []apiv1.ContainerPort{
{
Name: "http",
Protocol: apiv1.ProtocolTCP,
ContainerPort: 80,
},
},
},
},
},
},
},
}
// Create Deployment
fmt.Println("Creating deployment...")
result, err := deploymentsClient.Create(context.TODO(), deployment, metav1.CreateOptions{})
if err != nil {
panic(err)
}
fmt.Printf("Created deployment %q.\n", result.GetObjectMeta().GetName())
// Update Deployment
prompt()
fmt.Println("Updating deployment...")
// You have two options to Update() this Deployment:
//
// 1. Modify the "deployment" variable and call: Update(deployment).
// This works like the "kubectl replace" command and it overwrites/loses changes
// made by other clients between you Create() and Update() the object.
// 2. Modify the "result" returned by Get() and retry Update(result) until
// you no longer get a conflict error. This way, you can preserve changes made
// by other clients between Create() and Update(). This is implemented below
// using the retry utility package included with client-go. (RECOMMENDED)
//
// More Info:
// https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#concurrency-control-and-consistency
retryErr := retry.RetryOnConflict(retry.DefaultRetry, func() error {
// Retrieve the latest version of Deployment before attempting update
// RetryOnConflict uses exponential backoff to avoid exhausting the apiserver
result, getErr := deploymentsClient.Get(context.TODO(), "demo-deployment", metav1.GetOptions{})
if getErr != nil {
panic(fmt.Errorf("Failed to get latest version of Deployment: %v", getErr))
}
result.Spec.Replicas = int32Ptr(1) // reduce replica count
result.Spec.Template.Spec.Containers[0].Image = "nginx:1.13" // change nginx version
_, updateErr := deploymentsClient.Update(context.TODO(), result, metav1.UpdateOptions{})
return updateErr
})
if retryErr != nil {
panic(fmt.Errorf("Update failed: %v", retryErr))
}
fmt.Println("Updated deployment...")
// List Deployments
prompt()
fmt.Printf("Listing deployments in namespace %q:\n", apiv1.NamespaceDefault)
list, err := deploymentsClient.List(context.TODO(), metav1.ListOptions{})
if err != nil {
panic(err)
}
for _, d := range list.Items {
fmt.Printf(" * %s (%d replicas)\n", d.Name, *d.Spec.Replicas)
}
// Delete Deployment
prompt()
fmt.Println("Deleting deployment...")
deletePolicy := metav1.DeletePropagationForeground
if err := deploymentsClient.Delete(context.TODO(), "demo-deployment", metav1.DeleteOptions{
PropagationPolicy: &deletePolicy,
}); err != nil {
panic(err)
}
fmt.Println("Deleted deployment.")
}
func prompt() {
fmt.Printf("-> Press Return key to continue.")
scanner := bufio.NewScanner(os.Stdin)
for scanner.Scan() {
break
}
if err := scanner.Err(); err != nil {
panic(err)
}
fmt.Println()
}
func int32Ptr(i int32) *int32 { return &i }
4.deployment资源CRUD - dynamic方式
使用typed方式创建资源虽然方便，但是需要事先使用client-gen生成且会与某个特定版本耦合，不够通用，所以我们可以使用 unstructured.Unstructured 来表示集群中任意对象。
client, err := dynamic.NewForConfig(config)
if err != nil {
panic(err)
}
deploymentRes := schema.GroupVersionResource{Group: "apps", Version: "v1", Resource: "deployments"}
deployment := &unstructured.Unstructured{
Object: map[string]interface{}{
"apiVersion": "apps/v1",
"kind": "Deployment",
"metadata": map[string]interface{}{
"name": "demo-deployment",
},
"spec": map[string]interface{}{
"replicas": 2,
"selector": map[string]interface{}{
"matchLabels": map[string]interface{}{
"app": "demo",
},
},
"template": map[string]interface{}{
"metadata": map[string]interface{}{
"labels": map[string]interface{}{
"app": "demo",
},
},
"spec": map[string]interface{}{
"containers": []map[string]interface{}{
{
"name": "web",
"image": "nginx:1.12",
"ports": []map[string]interface{}{
{
"name": "http",
"protocol": "TCP",
"containerPort": 80,
},
},
},
},
},
},
},
},
}
// Create Deployment
fmt.Println("Creating deployment...")
result, err := client.Resource(deploymentRes).Namespace(apiv1.NamespaceDefault).Create(context.TODO(), deployment, metav1.CreateOptions{})
if err != nil {
panic(err)
}
fmt.Printf("Created deployment %q.\n", result.GetName())
5. discoveryClient
3-4小节我们学习了 typed client 和 dynamic client ，这两个client使用来操作集群中资源，比如创建 deployment，删除pod。discovery client 不同，他是用来发现服务端支持的组、版本、资源类型：
// Package discovery provides ways to discover server-supported
// API groups, versions and resources.
我们可以查询服务端支持的组与版本、某个组的资源列表
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()
// use the current context in kubeconfig
config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
if err != nil {
panic(err.Error())
}
// *查询服务端支持的组列表
discoveryClient := discovery.NewDiscoveryClientForConfigOrDie(config)
gs, err := discoveryClient.ServerGroups()
if err != nil {
panic(err.Error())
}
spew.Dump(gs.Groups)
// *查询core/v1 组下的资源列表
rs, err := discoveryClient.ServerResourcesForGroupVersion("v1")
if err != nil {
panic(err.Error())
}
for _, r := range rs.APIResources {
fmt.Println(r.Name)
}
}
// 输出支持的组列表
/*
(v1.APIGroup) &APIGroup{Name:apps,Versions:[]GroupVersionForDiscovery{GroupVersionForDiscovery{GroupVersion:apps/v1,Version:v1,},},PreferredVersion:GroupVersionForDiscovery{GroupVersion:apps/v1,Version:v1,},ServerAddressByClientCIDRs:[]ServerAddressByClientCIDR{},},
(v1.APIGroup) &APIGroup{Name:events.k8s.io,Versions:[]GroupVersionForDiscovery{GroupVersionForDiscovery{GroupVersion:events.k8s.io/v1,Version:v1,},},PreferredVersion:GroupVersionForDiscovery{GroupVersion:events.k8s.io/v1,Version:v1,},ServerAddressByClientCIDRs:[]ServerAddressByClientCIDR{},},
...
*/
// 输出core/v1组下的资源列表
/*
pods/status
podtemplates
replicationcontrollers
replicationcontrollers/scale
replicationcontrollers/status
resourcequotas
resourcequotas/status
secrets
serviceaccounts
...
*/
6. restClient
上面三种客户端都是基于 restClient 封装的，restClient 是 client-go 最基础的客户端，对http request 进行了封装，更加灵活，一般我们用不到。
// 根据配置信息构建restClient实例
restClient, err := rest.RESTClientFor(config)
if err!=nil {
panic(err.Error())
}
// 保存pod结果的数据结构实例
result := &corev1.PodList{}
// 指定namespace
namespace := "kube-system"
// 设置请求参数，然后发起请求
// GET请求
err = restClient.Get().
// 指定namespace，参考path : /api/v1/namespaces/{namespace}/pods
Namespace(namespace).
// 查找多个pod，参考path : /api/v1/namespaces/{namespace}/pods
Resource("pods").
// 指定大小限制和序列化工具
VersionedParams(&metav1.ListOptions{Limit:100}, scheme.ParameterCodec).
// 请求
Do(context.TODO()).
// 结果存入result
Into(result)
4、局限
使用 client 操作集群中资源会导致频繁的轮询，k8s client-go 包提供了更加高效的方式：informer 。
informer 提供了一种机制来监视 Kubernetes 集群内资源的变化并做出反应。它使开发人员能够接收有关各种 Kubernetes 对象（例如 Pod、服务、部署等）状态的实时更新。
Informer 将集群中的资源缓存在本地来减少频繁的API调用，提高性能并优化资源利用率。
原文地址：https://blog.csdn.net/chaoyueshijian/article/details/140688532
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