DiscoveryClient是什么

  • 我们前面学习的3种Client：RESTClient、Clientset、DynamicClient，都是用来操作 kubernetes 资源的，我们目前还缺少一个用于检索 kuberentes资源的 Client
  • DiscoveryClient 就是这样一个 Client。用于检索 kuberentes集群中支持的 API 资源的相关信息，例如版本、组、资源类型等。
  • DiscoveryClient 提供了一组方法来查询和获取这些信息，以便在编写 Controller 或 Operator 时，能够动态地了解集群中可用的资源。

DiscoveryClient结构体

  • 位于 staging/src/k8s.io/client-go/discovery/discovery_client.go
  • DiscoveryClient 结构体很简单
    • LegacyPrefix 字段表示旧版本资源的访问前缀，一般值都是/api。Kubernetes 1.16 以前，资源的访问前缀都是 /api，1.16及之后，全面改成 /apis，为了兼容旧资源，这里特意保存了一个常量字符串 /api
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      type DiscoveryClient struct {
      	restClient restclient.Interface

      	LegacyPrefix string
      	// Forces the client to request only "unaggregated" (legacy) discovery.
      	UseLegacyDiscovery bool
      }

DiscoveryClient的常用方法

1、discovery.NewDiscoveryClientForConfig()方法

  • 位于 /client-go/discovery/discovery_client.go，是一个函数，位于discovery包下，所以直接点就可以使用

  • 该方法用于创建一个 DiscoveryClient 实例，入参也是 *rest.Config 类型

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    func NewDiscoveryClientForConfig(c *restclient.Config) (*DiscoveryClient, error) {
    	config := *c
    	if err := setDiscoveryDefaults(&config); err != nil {
    		return nil, err
    	}
    	httpClient, err := restclient.HTTPClientFor(&config)
    	if err != nil {
    		return nil, err
    	}
    	return NewDiscoveryClientForConfigAndClient(&config, httpClient)
    }

    2、DiscoveryClient的实例方法

  • DiscoveryClient 实现了接口的所有方法，用于获取API资源的各种信息

    • ServerGroupsInterface等这些接口，内部也有很多方法
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      type DiscoveryInterface interface {
      	RESTClient() restclient.Interface
      	ServerGroupsInterface
      	ServerResourcesInterface
      	ServerVersionInterface
      	OpenAPISchemaInterface
      	OpenAPIV3SchemaInterface
      	// Returns copy of current discovery client that will only
      	// receive the legacy discovery format, or pointer to current
      	// discovery client if it does not support legacy-only discovery.
      	WithLegacy() DiscoveryInterface
      }

CachedDiscoveryClient 和 DiscoveryClient 的区别

  • 在查看 DiscoveryInterface 的时候，除了 DiscoveryClient，还有一个实现类 CachedDiscoveryClient

  • 顾名思义，CachedDiscoveryClient 就是实现了缓存机制的 DiscoveryClient 的封装

  • CachedDiscoveryClient 在 DiscoveryClient 的基础上增加了一层缓存，用于缓存获取的资源信息，以减少对 API Server 的频繁请求。

  • 在首次调用时，CachedDiscoveryClient 会从 API Server 获取资源信息，并将其缓存在本地。之后的调用会直接从缓存中获取资源信息，而不需要再次向 API Server 发送请求。

  • 因为 集群部署完成后，API 资源基本很少变化，所以缓存下来可以很好的提高请求效率。

  • kubectl 工具内部，kubectl api-versions命令其实就是使用了这个CachedDiscoveryClient，所以多次执行kubectl api-versions命令，其实只有第一次请求了API Server，后续都是直接使用的 本地缓存。

DiscoveryClient 使用示例

  • 需求：获取 当前kubernetes集群 的 所有资源列表
  • 代码编写
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    func main() {
    	// 1、先创建一个客户端配置config
    	config, err := clientcmd.BuildConfigFromFlags("", clientcmd.RecommendedHomeFile)
    	if err != nil {
    		panic(err.Error())
    	}

    	// 2、使用 discovery.NewDiscoveryClientForConfig()，创建一个 DiscoveryClient 对象
    	discoveryClient, err := discovery.NewDiscoveryClientForConfig(config)
    	if err != nil {
    		panic(err.Error())
    	}

    	// 3、使用 DiscoveryClient.ServerGroupsAndResources()，获取所有资源列表
    	_, resourceLists, err := discoveryClient.ServerGroupsAndResources()
    	if err != nil {
    		panic(err.Error())
    	}

    	// 4、遍历资源列表，打印出资源组和资源名称
    	for _, resource := range resourceLists {
    		fmt.Printf("resource groupVersion: %s\n", resource.GroupVersion)
    		for _, resource := range resource.APIResources {
    			fmt.Printf("resource name: %s\n", resource.Name)
    		}
    		fmt.Println("--------------------------")
    	}
    }
    输出结果
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resource groupVersion: v1
resource name: bindings
resource name: componentstatuses
resource name: configmaps
resource name: endpoints
resource name: events
resource name: limitranges
resource name: namespaces
resource name: namespaces/finalize
resource name: namespaces/status
resource name: nodes
resource name: nodes/proxy
resource name: nodes/status
resource name: persistentvolumeclaims
resource name: persistentvolumeclaims/status
resource name: persistentvolumes
resource name: persistentvolumes/status
resource name: pods
resource name: pods/attach
resource name: pods/binding
resource name: pods/eviction
resource name: pods/exec
resource name: pods/log
resource name: pods/portforward
resource name: pods/proxy
resource name: pods/status
resource name: podtemplates
resource name: replicationcontrollers
resource name: replicationcontrollers/scale
resource name: replicationcontrollers/status
resource name: resourcequotas
resource name: resourcequotas/status
resource name: secrets
resource name: serviceaccounts
resource name: services
resource name: services/proxy
resource name: services/status
--------------------------
resource groupVersion: apiregistration.k8s.io/v1
resource name: apiservices
resource name: apiservices/status
--------------------------
resource groupVersion: apiregistration.k8s.io/v1beta1
resource name: apiservices
resource name: apiservices/status
--------------------------
resource groupVersion: extensions/v1beta1
resource name: ingresses
resource name: ingresses/status
--------------------------
resource groupVersion: apps/v1
resource name: controllerrevisions
resource name: daemonsets
resource name: daemonsets/status
resource name: deployments
resource name: deployments/scale
resource name: deployments/status
resource name: replicasets
resource name: replicasets/scale
resource name: replicasets/status
resource name: statefulsets
resource name: statefulsets/scale
resource name: statefulsets/status
--------------------------
resource groupVersion: events.k8s.io/v1beta1
resource name: events
--------------------------
resource groupVersion: authentication.k8s.io/v1
resource name: tokenreviews
--------------------------
resource groupVersion: authentication.k8s.io/v1beta1
resource name: tokenreviews
--------------------------
resource groupVersion: authorization.k8s.io/v1
resource name: localsubjectaccessreviews
resource name: selfsubjectaccessreviews
resource name: selfsubjectrulesreviews
resource name: subjectaccessreviews
--------------------------
resource groupVersion: authorization.k8s.io/v1beta1
resource name: localsubjectaccessreviews
resource name: selfsubjectaccessreviews
resource name: selfsubjectrulesreviews
resource name: subjectaccessreviews
--------------------------
resource groupVersion: autoscaling/v1
resource name: horizontalpodautoscalers
resource name: horizontalpodautoscalers/status
--------------------------
resource groupVersion: autoscaling/v2beta1
resource name: horizontalpodautoscalers
resource name: horizontalpodautoscalers/status
--------------------------
resource groupVersion: autoscaling/v2beta2
resource name: horizontalpodautoscalers
resource name: horizontalpodautoscalers/status
--------------------------
resource groupVersion: batch/v1
resource name: jobs
resource name: jobs/status
--------------------------
resource groupVersion: batch/v1beta1
resource name: cronjobs
resource name: cronjobs/status
--------------------------
resource groupVersion: certificates.k8s.io/v1beta1
resource name: certificatesigningrequests
resource name: certificatesigningrequests/approval
resource name: certificatesigningrequests/status
--------------------------
resource groupVersion: networking.k8s.io/v1
resource name: networkpolicies
--------------------------
resource groupVersion: networking.k8s.io/v1beta1
resource name: ingresses
resource name: ingresses/status
--------------------------
resource groupVersion: policy/v1beta1
resource name: poddisruptionbudgets
resource name: poddisruptionbudgets/status
resource name: podsecuritypolicies
--------------------------
resource groupVersion: rbac.authorization.k8s.io/v1
resource name: clusterrolebindings
resource name: clusterroles
resource name: rolebindings
resource name: roles
--------------------------
resource groupVersion: rbac.authorization.k8s.io/v1beta1
resource name: clusterrolebindings
resource name: clusterroles
resource name: rolebindings
resource name: roles
--------------------------
resource groupVersion: storage.k8s.io/v1
resource name: csinodes
resource name: storageclasses
resource name: volumeattachments
resource name: volumeattachments/status
--------------------------
resource groupVersion: storage.k8s.io/v1beta1
resource name: csidrivers
resource name: csinodes
resource name: storageclasses
resource name: volumeattachments
--------------------------
resource groupVersion: admissionregistration.k8s.io/v1
resource name: mutatingwebhookconfigurations
resource name: validatingwebhookconfigurations
--------------------------
resource groupVersion: admissionregistration.k8s.io/v1beta1
resource name: mutatingwebhookconfigurations
resource name: validatingwebhookconfigurations
--------------------------
resource groupVersion: apiextensions.k8s.io/v1
resource name: customresourcedefinitions
resource name: customresourcedefinitions/status
--------------------------
resource groupVersion: apiextensions.k8s.io/v1beta1
resource name: customresourcedefinitions
resource name: customresourcedefinitions/status
--------------------------
resource groupVersion: scheduling.k8s.io/v1
resource name: priorityclasses
--------------------------
resource groupVersion: scheduling.k8s.io/v1beta1
resource name: priorityclasses
--------------------------
resource groupVersion: coordination.k8s.io/v1
resource name: leases
--------------------------
resource groupVersion: coordination.k8s.io/v1beta1
resource name: leases
--------------------------
resource groupVersion: node.k8s.io/v1beta1
resource name: runtimeclasses
--------------------------
resource groupVersion: discovery.k8s.io/v1beta1
resource name: endpointslices
--------------------------