理解 Kubernetes 的 API Schema

1、schema的定义

而 kubernetes 中资源对象即 Group Version Kind 这些被定义在 staging/src/k8s.io/api/type.go 中，即平时所操作的 yaml 文件，例如

apiVersion: apps/v1
kind: Deployment  
metadata:
  name:  ngx
  namespace: default
spec:
  selector:  
    matchLabels:
      app: ngx
  template:  
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: ngx-schema
        image: nginx
        ports:
        - containerPort: 80

而对应的的即为 TypeMeta 、ObjectMeta 和 DeploymentSpec，TypeMeta 为 kind 与 apiserver，ObjectMeta 为 Name 、

Namespace CreationTimestamp 等段。

DeploymentSpec 则对应了 yaml 中的 spec，而整个 yaml 组成了 一个 k8s 的资源对象。

type Deployment struct {
    metav1.TypeMeta `json:",inline"`
    // Standard object metadata.
    // +optional
    metav1.ObjectMeta `json:"metadata,omitempty" protobuf:"bytes,1,opt,name=metadata"`

    // Specification of the desired behavior of the Deployment.
    // +optional
    Spec DeploymentSpec `json:"spec,omitempty" protobuf:"bytes,2,opt,name=spec"`

    // Most recently observed status of the Deployment.
    // +optional
    Status DeploymentStatus `json:"status,omitempty" protobuf:"bytes,3,opt,name=status"`
}

register.go 则是将对应的资源类型注册到 schema 中的类

var (
    // TODO: move SchemeBuilder with zz_generated.deepcopy.go to k8s.io/api.
    // localSchemeBuilder and AddToScheme will stay in k8s.io/kubernetes.
    SchemeBuilder      = runtime.NewSchemeBuilder(addKnownTypes)
    localSchemeBuilder = &SchemeBuilder
    AddToScheme        = localSchemeBuilder.AddToScheme
)

// Adds the list of known types to the given scheme.
func addKnownTypes(scheme *runtime.Scheme) error {
    scheme.AddKnownTypes(SchemeGroupVersion,
        &Deployment{},
        &DeploymentList{},
        &StatefulSet{},
        &StatefulSetList{},
        &DaemonSet{},
        &DaemonSetList{},
        &ReplicaSet{},
        &ReplicaSetList{},
        &ControllerRevision{},
        &ControllerRevisionList{},
    )
    metav1.AddToGroupVersion(scheme, SchemeGroupVersion)
    return nil
}

而 apimachinery 包则是 schema 的实现，通过看其内容可以发现，kubernetes 中 schema 就是 GVK 的属性约束 与 GVR 之间的映射

通过示例了解 schema

例如在 apps/v1/deployment 这个资源，在代码中表示 k8s.io/api/apps/v1/types.go ，如果需要对其资源进行扩展那么需要怎么做？如，建立一个 StateDeplyment 资源

type Deployment struct {
    metav1.TypeMeta `json:",inline"`
    // Standard object metadata.
    // +optional
    metav1.ObjectMeta `json:"metadata,omitempty" protobuf:"bytes,1,opt,name=metadata"`

如上述代码所示，Deployment 中的 metav1.TypeMeta 和 metav1.ObjectMeta

 

那么我们复制一个 Deployment 为 StateDeployment，注意，因为 Deployment 的两个属性， metav1.TypeMeta 和 metav1.ObjectMeta 分别实现了不同的方法，如图所示

 所以在实现方法时，需要实现 DeepCopyinfo ， DeepCopy 和继承接口 Object 的 DeepCopyObject 方法

// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
func (in *StateDeployment) DeepCopyInto(out *StateDeployment) {
    *out = *in
    out.TypeMeta = in.TypeMeta
    in.ObjectMeta.DeepCopyInto(&out.ObjectMeta)
    in.Spec.DeepCopyInto(&out.Spec)
    in.Status.DeepCopyInto(&out.Status)
    return
}

// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new StateDeployment.
func (in *StateDeployment) DeepCopy() *StateDeployment {
    if in == nil {
        return nil
    }
    out := new(StateDeployment)
    in.DeepCopyInto(out)
    return out
}

// DeepCopyObject is an autogenerated deepcopy function, copying the receiver, creating a new runtime.Object.
func (in *StateDeployment) DeepCopyObject() runtime.Object {
    if c := in.DeepCopy(); c != nil {
        return c
    }
    return nil
}

那么扩展一个资源的整个流为：

• 资源类型在：k8s.io/api/{Group}/types.go
• 资料类型的实现接口 k8s.io/apimachinery/pkg/runtime/interfaces.go.Object
• 其中是基于 Deployment 的类型，metav1.TypeMeta 和 metav1.ObjectMeta
• metav1.TypeMeta 实现了 GetObjectKind() ；metav1.ObjectMeta 实现了 DeepCopyinfo=()，DeepCopy() ，还需要实现 DeepCopyObject()
• 最后注册资源到 schema 中 k8s.io/api/apps/v1/register.go