K8S中为什么需要Unstructured对象

本文主要是介绍K8S中为什么需要Unstructured对象，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

熟悉client-go的同学都知道，不止有Deployment、Pod这些结构化对象，也提供了unstructured.Unstructured对象，那么为什么需要非结构对象？

Structured vs Unstructured

结构化对象是指可以用Go Struct表示的对象，比如Deployment在k8s.io/api/apps/v1定义

type Deployment struct {metav1.TypeMeta `json:",inline"`// Standard object's metadata.// More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata// +optionalmetav1.ObjectMeta `json:"metadata,omitempty" protobuf:"bytes,1,opt,name=metadata"`...
}

我们可以直接通过appsv1.Deployment来安全地定义Deployment的各个字段，通常创建过程如下：

clientset, err := kubernetes.NewForConfig(config)deployment := &appsv1.Deployment{}
deployment.Name = "example"
deployment.Spec = appsv1.DeploymentSpec{...
}clientset.AppsV1().Deployments(apiv1.NamespaceDefault).Create(deployment)

而对于Unstructured定义在k8s.io/apimachinery/pkg/apis/meta/v1/unstructured中

type Unstructured struct {// Object is a JSON compatible map with string, float, int, bool, []interface{}, or// map[string]interface{}// children.Object map[string]interface{}
}

通过定义map[string]interface{}可以来表示任意的JSON/YAML对象，而不需要引用Go Struct。可以通过Dynamic client来创建非结构化对象，以下是使用Unstructured创建Deployment的样例。

client, _ := dynamic.NewForConfig(config)
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,...}}
}client.Resource(deploymentRes).Namespace(namespace).Create(context.TODO(), deployment, metav1.CreateOptions{})

Why

那么什么情况下需要使用到Unstructured对象呢，结构化对象有着安全地类型校验，通过clientset可以方便地增删改查。而非结构化对象只能手动设置GVR、通过map[string]interface{}设置各个字段。

假想你作为一个Paas平台的开发者，需要为每个用户传入的YAML/JSON资源添加label，比如添加user信息creator=xxx。如果用户只能创建Deployment，那么我们可以将资源解析成appsv1.Deployment{}对象，再添加label。但是通常会传入多种资源，不仅有内置的Deployment、Service等，也可能会包含自定义资源。由于不确定资源类型，我们只能通过Unstructured对象来解析。

const manifest = `
apiVersion: apps/v1
kind: Deployment
metadata:name: example
spec:...
`
// convert yaml to unstructured
obj := &unstructured.Unstructured{}
dec := yaml.NewDecodingSerializer(unstructured.UnstructuredJSONScheme)
dec.Decode([]byte(manifest), nil, obj)// add label
labels := obj.GetLabels()
labels["creator"]="userxxx"// set label
obj.SetLabels(labels)dynamicClient.Resource().Namespace(namespace).Create(context.TODO(), obj, metav1.CreateOptions{})

当实现对多种资源的通用处理（上面的示例），或者运行时才能确定的对象（例如根据配置监听不同对象），又或者不愿引入额外的依赖（处理大量的CRD），可以使用Unstructured对象来处理以上情况。

How

不管是结构化对象还是非结构化，最终会调用k8s的Rest API，例如Create Deployment时

POST /apis/apps/v1/namespaces/{namespace}/deployments/{name}

K8s中GVR(GroupVersionResource)可以唯一表征资源对象，用来组成Rest API, 如上Group为apps、Version为v1、Resource是deployments；GVK(GroupVersionKind)可以来标识类型（如Deployment）。Resource与Kind的对应关系可以通过kubectl api-resources查看。

~ kubectl api-resources --api-group apps
NAME                  SHORTNAMES   APIVERSION   NAMESPACED   KIND
controllerrevisions                apps/v1      true         ControllerRevision
daemonsets            ds           apps/v1      true         DaemonSet
deployments           deploy       apps/v1      true         Deployment
replicasets           rs           apps/v1      true         ReplicaSet
statefulsets          sts          apps/v1      true         StatefulSet

对于结构化对象，使用clientset可以获取到GVR，最后调用restClient组成到Rest API

clientset.AppsV1().Deployments(namespace).Create(deployment)// Create takes the representation of a deployment and creates it.  Returns the server's representation of the deployment, and an error, if there is any.
func (c *deployments) Create(ctx context.Context, deployment *v1.Deployment, opts metav1.CreateOptions) (result *v1.Deployment, err error) {result = &v1.Deployment{}err = c.client.Post().Namespace(c.ns).Resource("deployments"). // Resource设置VersionedParams(&opts, scheme.ParameterCodec).Body(deployment).Do(ctx).Into(result)return
}

对于非结构化对象，需要用户手动填充GVR，如果只知道GVK可以通过restMapping获取

deploymentRes := schema.GroupVersionResource{Group: "apps", Version: "v1", Resource: "deployments"}dynamicClient.Resource().Namespace(namespace).Create()// Create具体实现
func (c *dynamicResourceClient) Create(ctx context.Context, obj *unstructured.Unstructured, opts metav1.CreateOptions, subresources ...string) (*unstructured.Unstructured, error) {outBytes, err := runtime.Encode(unstructured.UnstructuredJSONScheme, obj)name := ""if len(subresources) > 0 {accessor, err := meta.Accessor(obj)name = accessor.GetName()}// 调用restClientresult := c.client.client.Post().AbsPath(append(c.makeURLSegments(name), subresources...)...).Body(outBytes).SpecificallyVersionedParams(&opts, dynamicParameterCodec, versionV1).Do(ctx)// ...
}