使用client-go 之dynamicclient（二)

在開發中碰到一個場景，在一個yaml文件中同時定義了deployment和service兩種資源類型（可能還有更多個），然後需要對該yaml文件進行解析，並對解析出的資源對象進行過一系列操作。如果使用typed clients你的代碼也許會像下面這樣：

//僞代碼
var deployment apps_v1.Deployment{}
var service core_v1.Service{}
var Raw []byte
var data map[string]interface{}

clientset, err := kubernetes.NewForConfig(&config)
b,err :=ioutil.ReadFile("template.yaml")
d := yaml.NewYAMLOrJSONDecoder(bytes.NewReader(b), 4096)

for {
    
    d.decode(&Raw)
    json.Unmarshal(Raw, &data)
    if data["kind"] == "Deployment"{
         //處理邏輯
        clientset.AppsV1.deployment（）
    }
    if data["kind"] == "Service"{
        //處理邏輯
        clientset.CoreV1.service（）
    }
    
}

如果yaml文件中還有ingress,configmap等等多個資源類型，每增加一種，你都需要重新定義一個資源對象，增加一個判斷。是不是相當繁瑣？

還好client-go中提供了dynamic client,使用該clientset後，代碼變成如下：

//僞代碼
client, err := dynamic.NewForConfig(config)

resp, err =client.Resource(gvr).Namespace(namespace).Get(name,metav1.GetOptions{})

看到沒，接下去只需要解析出gvr對象，就能對所有資源類型進行響應操作，那接下來我們解決下一個問題，怎麼解析出gvr。

在解析出gvr對象前，我們先了解下什麼是RESTMapper。RESTMapper是一個interface，定義在/pkg/meta/interfaces.go中:

// RESTMapper allows clients to map resources to kind, and map kind and version
// to interfaces for manipulating those objects. It is primarily intended for
// consumers of Kubernetes compatible REST APIs as defined in docs/devel/api-conventions.md.
//
// The Kubernetes API provides versioned resources and object kinds which are scoped
// to API groups. In other words, kinds and resources should not be assumed to be
// unique across groups.
//
// TODO: split into sub-interfaces
type RESTMapper interface {
	// KindFor takes a partial resource and returns the single match.  Returns an error if there are multiple matches
	KindFor(resource schema.GroupVersionResource) (schema.GroupVersionKind, error)

	// KindsFor takes a partial resource and returns the list of potential kinds in priority order
	KindsFor(resource schema.GroupVersionResource) ([]schema.GroupVersionKind, error)

	// ResourceFor takes a partial resource and returns the single match.  Returns an error if there are multiple matches
	ResourceFor(input schema.GroupVersionResource) (schema.GroupVersionResource, error)

	// ResourcesFor takes a partial resource and returns the list of potential resource in priority order
	ResourcesFor(input schema.GroupVersionResource) ([]schema.GroupVersionResource, error)

	// RESTMapping identifies a preferred resource mapping for the provided group kind.
	RESTMapping(gk schema.GroupKind, versions ...string) (*RESTMapping, error)
	// RESTMappings returns all resource mappings for the provided group kind if no
	// version search is provided. Otherwise identifies a preferred resource mapping for
	// the provided version(s).
	RESTMappings(gk schema.GroupKind, versions ...string) ([]*RESTMapping, error)

	ResourceSingularizer(resource string) (singular string, err error)
}

是不是在這個接口中看到了gvk和gvr了，我們再看下RESTMapping是什麼：

// RESTMapping contains the information needed to deal with objects of a specific
// resource and kind in a RESTful manner.
type RESTMapping struct {
	// Resource is the GroupVersionResource (location) for this endpoint
	Resource schema.GroupVersionResource

	// GroupVersionKind is the GroupVersionKind (data format) to submit to this endpoint
	GroupVersionKind schema.GroupVersionKind

	// Scope contains the information needed to deal with REST Resources that are in a resource hierarchy
	Scope RESTScope
}

也就是說我們可以通過RESTMapper接口的RESTMapping方法通過gvk獲得gvr。剩下的問題就是如何解析出gvk以及創建RESTMapper對象，我們通過代碼直觀展現：

//僞代碼
restMapperRes, err := restmapper.GetAPIGroupResources(dc)
	
restMapper := restmapper.NewDiscoveryRESTMapper(restMapperRes)

for {
    //yaml解析成[]byte
    obj, gvk, err := unstructured.UnstructuredJSONScheme.Decode([]byte, nil, nil)
    mapping, err := restMapper.RESTMapping(gvk.GroupKind(), gvk.Version)
    resp,err :=dclient.Resource(mapping.Resource).Namespace(namespace).Get(name,metav1.GetOptions{})

}

這樣在單個yaml文件中定義再多的資源類型也不怕了

參考：https://fankangbest.github.io/2017/07/22/RESTMapper%E8%A7%A3%E8%AF%BB(%E4%B8%80)-DefaultRESTMapper-v1-5-2/

https://www.kubernetes.org.cn/1309.html