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Kubernetes编程——client-go基础—— ObjectMeta

ObjectMeta

https://github.com/kubernetes/apimachinery/blob/release-1.27/pkg/apis/meta/v1/types.go

我理解意思是说：在 Kubernetes 中，ObjectMeta 是一个结构体，用于表示资源对象的元数据，例如 Pod、Service 和 Deployment 等。ObjectMeta 结构体包含了以下字段：

- Name：资源对象的名称。
- Namespace：资源对象所属的命名空间。
- Labels：带有键值对的标签，用于标识和选择资源对象。
- Annotations：带有键值对的注释，用于提供关于资源对象的附加信息。
- OwnerReferences：指向拥有当前资源对象的其他资源对象的引用。
- CreationTimestamp：资源对象的创建时间戳。
- Finalizers：资源对象的终结器列表，控制资源对象的生命周期。

ObjectMeta 使得 Kubernetes 可以管理和维护资源对象的元数据信息，从而更好地管理和调度这些对象。

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出自：https://github.com/kubernetes/apimachinery/blob/release-1.27/pkg/apis/meta/v1/types.go<br><br>// ObjectMeta is metadata that all persisted resources must have, which includes all objects
// users must create.
type ObjectMeta struct {
    // Name must be unique within a namespace. Is required when creating resources, although
    // some resources may allow a client to request the generation of an appropriate name
    // automatically. Name is primarily intended for creation idempotence and configuration
    // definition.
    // Cannot be updated.
    // More info: https://kubernetes.io/docs/concepts/overview/working-with-objects/names#names
    // +optional
    Name string `json:"name,omitempty" protobuf:"bytes,1,opt,name=name"`
 
    // GenerateName is an optional prefix, used by the server, to generate a unique
    // name ONLY IF the Name field has not been provided.
    // If this field is used, the name returned to the client will be different
    // than the name passed. This value will also be combined with a unique suffix.
    // The provided value has the same validation rules as the Name field,
    // and may be truncated by the length of the suffix required to make the value
    // unique on the server.
    //
    // If this field is specified and the generated name exists, the server will return a 409.
    //
    // Applied only if Name is not specified.
    // More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#idempotency
    // +optional
    GenerateName string `json:"generateName,omitempty" protobuf:"bytes,2,opt,name=generateName"`
 
    // Namespace defines the space within which each name must be unique. An empty namespace is
    // equivalent to the "default" namespace, but "default" is the canonical representation.
    // Not all objects are required to be scoped to a namespace - the value of this field for
    // those objects will be empty.
    //
    // Must be a DNS_LABEL.
    // Cannot be updated.
    // More info: https://kubernetes.io/docs/concepts/overview/working-with-objects/namespaces
    // +optional
    Namespace string `json:"namespace,omitempty" protobuf:"bytes,3,opt,name=namespace"`
 
    // Deprecated: selfLink is a legacy read-only field that is no longer populated by the system.
    // +optional
    SelfLink string `json:"selfLink,omitempty" protobuf:"bytes,4,opt,name=selfLink"`
 
    // UID is the unique in time and space value for this object. It is typically generated by
    // the server on successful creation of a resource and is not allowed to change on PUT
    // operations.
    //
    // Populated by the system.
    // Read-only.
    // More info: https://kubernetes.io/docs/concepts/overview/working-with-objects/names#uids
    // +optional
    UID types.UID `json:"uid,omitempty" protobuf:"bytes,5,opt,name=uid,casttype=k8s.io/kubernetes/pkg/types.UID"`
 
    // An opaque value that represents the internal version of this object that can
    // be used by clients to determine when objects have changed. May be used for optimistic
    // concurrency, change detection, and the watch operation on a resource or set of resources.
    // Clients must treat these values as opaque and passed unmodified back to the server.
    // They may only be valid for a particular resource or set of resources.
    //
    // Populated by the system.
    // Read-only.
    // Value must be treated as opaque by clients and .
    // More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#concurrency-control-and-consistency
    // +optional
    ResourceVersion string `json:"resourceVersion,omitempty" protobuf:"bytes,6,opt,name=resourceVersion"`
 
    // A sequence number representing a specific generation of the desired state.
    // Populated by the system. Read-only.
    // +optional
    Generation int64 `json:"generation,omitempty" protobuf:"varint,7,opt,name=generation"`
 
    // CreationTimestamp is a timestamp representing the server time when this object was
    // created. It is not guaranteed to be set in happens-before order across separate operations.
    // Clients may not set this value. It is represented in RFC3339 form and is in UTC.
    //
    // Populated by the system.
    // Read-only.
    // Null for lists.
    // More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
    // +optional
    CreationTimestamp Time `json:"creationTimestamp,omitempty" protobuf:"bytes,8,opt,name=creationTimestamp"`
 
    // DeletionTimestamp is RFC 3339 date and time at which this resource will be deleted. This
    // field is set by the server when a graceful deletion is requested by the user, and is not
    // directly settable by a client. The resource is expected to be deleted (no longer visible
    // from resource lists, and not reachable by name) after the time in this field, once the
    // finalizers list is empty. As long as the finalizers list contains items, deletion is blocked.
    // Once the deletionTimestamp is set, this value may not be unset or be set further into the
    // future, although it may be shortened or the resource may be deleted prior to this time.
    // For example, a user may request that a pod is deleted in 30 seconds. The Kubelet will react
    // by sending a graceful termination signal to the containers in the pod. After that 30 seconds,
    // the Kubelet will send a hard termination signal (SIGKILL) to the container and after cleanup,
    // remove the pod from the API. In the presence of network partitions, this object may still
    // exist after this timestamp, until an administrator or automated process can determine the
    // resource is fully terminated.
    // If not set, graceful deletion of the object has not been requested.
    //
    // Populated by the system when a graceful deletion is requested.
    // Read-only.
    // More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
    // +optional
    DeletionTimestamp *Time `json:"deletionTimestamp,omitempty" protobuf:"bytes,9,opt,name=deletionTimestamp"`
 
    // Number of seconds allowed for this object to gracefully terminate before
    // it will be removed from the system. Only set when deletionTimestamp is also set.
    // May only be shortened.
    // Read-only.
    // +optional
    DeletionGracePeriodSeconds *int64 `json:"deletionGracePeriodSeconds,omitempty" protobuf:"varint,10,opt,name=deletionGracePeriodSeconds"`
 
    // Map of string keys and values that can be used to organize and categorize
    // (scope and select) objects. May match selectors of replication controllers
    // and services.
    // More info: https://kubernetes.io/docs/concepts/overview/working-with-objects/labels
    // +optional
    Labels map[string]string `json:"labels,omitempty" protobuf:"bytes,11,rep,name=labels"`
 
    // Annotations is an unstructured key value map stored with a resource that may be
    // set by external tools to store and retrieve arbitrary metadata. They are not
    // queryable and should be preserved when modifying objects.
    // More info: https://kubernetes.io/docs/concepts/overview/working-with-objects/annotations
    // +optional
    Annotations map[string]string `json:"annotations,omitempty" protobuf:"bytes,12,rep,name=annotations"`
 
    // List of objects depended by this object. If ALL objects in the list have
    // been deleted, this object will be garbage collected. If this object is managed by a controller,
    // then an entry in this list will point to this controller, with the controller field set to true.
    // There cannot be more than one managing controller.
    // +optional
    // +patchMergeKey=uid
    // +patchStrategy=merge
    OwnerReferences []OwnerReference `json:"ownerReferences,omitempty" patchStrategy:"merge" patchMergeKey:"uid" protobuf:"bytes,13,rep,name=ownerReferences"`
 
    // Must be empty before the object is deleted from the registry. Each entry
    // is an identifier for the responsible component that will remove the entry
    // from the list. If the deletionTimestamp of the object is non-nil, entries
    // in this list can only be removed.
    // Finalizers may be processed and removed in any order.  Order is NOT enforced
    // because it introduces significant risk of stuck finalizers.
    // finalizers is a shared field, any actor with permission can reorder it.
    // If the finalizer list is processed in order, then this can lead to a situation
    // in which the component responsible for the first finalizer in the list is
    // waiting for a signal (field value, external system, or other) produced by a
    // component responsible for a finalizer later in the list, resulting in a deadlock.
    // Without enforced ordering finalizers are free to order amongst themselves and
    // are not vulnerable to ordering changes in the list.
    // +optional
    // +patchStrategy=merge
    Finalizers []string `json:"finalizers,omitempty" patchStrategy:"merge" protobuf:"bytes,14,rep,name=finalizers"`
 
    // Tombstone: ClusterName was a legacy field that was always cleared by
    // the system and never used.
    // ClusterName string `json:"clusterName,omitempty" protobuf:"bytes,15,opt,name=clusterName"`
 
    // ManagedFields maps workflow-id and version to the set of fields
    // that are managed by that workflow. This is mostly for internal
    // housekeeping, and users typically shouldn't need to set or
    // understand this field. A workflow can be the user's name, a
    // controller's name, or the name of a specific apply path like
    // "ci-cd". The set of fields is always in the version that the
    // workflow used when modifying the object.
    //
    // +optional
    ManagedFields []ManagedFieldsEntry `json:"managedFields,omitempty" protobuf:"bytes,17,rep,name=managedFields"`
}

在 JSON 或 YAML 中，这些字段位于 metadata 字段中。deployment 对象为例，metav1.ObjectMeta 中存储了如下信息：

metadata:
  namespace: default
  name: example

通常来说， metadata 字段中存储了各种元信息，包括名字、命名空间、资源版本（不是API组版本）、各种时间戳以及一些通用的标签和注解，它们都是 ObjectMeta 的一部分。

client-go 中的代码通常不直接对 ObjectMeta 字段进行读写操作。ObjectMeta 字段的值是由 Kubernetes 系统自动生成和管理的，用于确保整个系统的一致性和正确性。

在 ObjectMeta 中，resourceVersion 是用来跟踪对象在 Kubernetes 集群中的版本信息的重要字段。每个对象的 ObjectMeta 对应着 etcd 中的一个键，而 resourceVersion 的值正是来自于 etcd。resourceVersion 字段用于比较和解决并发更新的冲突，确保更新操作是基于最新的数据。

import (
    "fmt"
    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "k8s.io/client-go/kubernetes"
    )
 
    func main() {
    // 创建 Kubernetes 客户端
    clientset, _ := kubernetes.NewForConfig(config)
 
    // 获取 Pod 的元数据
    pod, _ := clientset.CoreV1().Pods("default").Get(context.TODO(), "my-pod", metav1.GetOptions{})
 
    // 检查当前资源版本
    fmt.Println("Current Resource Version:", pod.ObjectMeta.ResourceVersion)
 
    // 修改 Pod 对象
    pod.ObjectMeta.Labels["new-label"] = "new-value"
    // ...
 
    // 更新 Pod 对象
    updatedPod, _ := clientset.CoreV1().Pods("default").Update(context.TODO(), pod, metav1.UpdateOptions{})
    fmt.Println("Updated Resource Version:", updatedPod.ObjectMeta.ResourceVersion)
    // ...
    }