k8s源码学习--三大核心数据结构

三大核心数据结构是什么？

Group（APIGroup） 资源组
Version（APIVersions） 资源版本
Resource/SubResource（APIResource） 资源/子资源
Kind 资源种类，描述Resource的种类
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完整表现形式：资源组/资源版本/资源/子资源
<group>/<version>/<resource>/<subresource>
apps/v1/deployments/status

三大核心数据结构如何定义

以github当前最新版本Kubernetes v1.23.3为例

Group资源组

代码：vendor/k8s.io/apimachinery/pkg/apis/meta/v1/types.go

// APIGroup contains the name, the supported versions, and the preferred version
// of a group.
type APIGroup struct {
    TypeMeta `json:",inline"`
    // name is the name of the group.
    Name string `json:"name" protobuf:"bytes,1,opt,name=name"`
    // versions are the versions supported in this group.
    Versions []GroupVersionForDiscovery `json:"versions" protobuf:"bytes,2,rep,name=versions"`
    // preferredVersion is the version preferred by the API server, which
    // probably is the storage version.
    // +optional
    PreferredVersion GroupVersionForDiscovery `json:"preferredVersion,omitempty" protobuf:"bytes,3,opt,name=preferredVersion"`
    // a map of client CIDR to server address that is serving this group.
    // This is to help clients reach servers in the most network-efficient way possible.
    // Clients can use the appropriate server address as per the CIDR that they match.
    // In case of multiple matches, clients should use the longest matching CIDR.
    // The server returns only those CIDRs that it thinks that the client can match.
    // For example: the master will return an internal IP CIDR only, if the client reaches the server using an internal IP.
    // Server looks at X-Forwarded-For header or X-Real-Ip header or request.RemoteAddr (in that order) to get the client IP.
    // +optional
    ServerAddressByClientCIDRs []ServerAddressByClientCIDR `json:"serverAddressByClientCIDRs,omitempty" protobuf:"bytes,4,rep,name=serverAddressByClientCIDRs"`
}

资源版本：Version

代码：vendor/k8s.io/apimachinery/pkg/apis/meta/v1/types.go
Alpha，第一阶段，内部测试，v1alpha1、v1alpha2、v2alpha1
Beta ，第二阶段，修复很不不完善的地方，仍可能有缺陷，v1beta1、v1beta2、v2beta1
Stable ，第三阶段，达到一定成熟度，可稳定运行，v1,v2,v3

// APIVersions lists the versions that are available, to allow clients to
// discover the API at /api, which is the root path of the legacy v1 API.
//
// +protobuf.options.(gogoproto.goproto_stringer)=false
// +k8s:deepcopy-gen:interfaces=k8s.io/apimachinery/pkg/runtime.Object
type APIVersions struct {
    TypeMeta `json:",inline"`
    // versions are the api versions that are available.
    Versions []string `json:"versions" protobuf:"bytes,1,rep,name=versions"`
    // a map of client CIDR to server address that is serving this group.
    // This is to help clients reach servers in the most network-efficient way possible.
    // Clients can use the appropriate server address as per the CIDR that they match.
    // In case of multiple matches, clients should use the longest matching CIDR.
    // The server returns only those CIDRs that it thinks that the client can match.
    // For example: the master will return an internal IP CIDR only, if the client reaches the server using an internal IP.
    // Server looks at X-Forwarded-For header or X-Real-Ip header or request.RemoteAddr (in that order) to get the client IP.
    ServerAddressByClientCIDRs []ServerAddressByClientCIDR `json:"serverAddressByClientCIDRs" protobuf:"bytes,2,rep,name=serverAddressByClientCIDRs"`
}

资源 Resource

一个资源被实例化后被称为资源对象（Resource object，由资源组+资源版本+资源种类组成<group>/<version>,Kind<kind>，例如deployment的资源对象是：apps/v1,Kind=deployment），所有资源对象都是一个实体（Entity），k8s用Entity表示当前状态，可以通过k8s Apiserver查询和更新实体，分为：
持久性实体：Persistent Entity （例如：Deployment，异常退出后会被重新创建）
短暂性实体：Ephemeral Entity （例如：pod，异常退出后不会重新创建）
代码：k8s.io/apimachinery/pkg/apis/meta/v1/types.go

// APIResource specifies the name of a resource and whether it is namespaced.
type APIResource struct {
    // name is the plural name of the resource.
    Name string `json:"name" protobuf:"bytes,1,opt,name=name"`
    // singularName is the singular name of the resource.  This allows clients to handle plural and singular opaquely.
    // The singularName is more correct for reporting status on a single item and both singular and plural are allowed
    // from the kubectl CLI interface.
    SingularName string `json:"singularName" protobuf:"bytes,6,opt,name=singularName"`
    // namespaced indicates if a resource is namespaced or not.
    Namespaced bool `json:"namespaced" protobuf:"varint,2,opt,name=namespaced"`
    // group is the preferred group of the resource.  Empty implies the group of the containing resource list.
    // For subresources, this may have a different value, for example: Scale".
    Group string `json:"group,omitempty" protobuf:"bytes,8,opt,name=group"`
    // version is the preferred version of the resource.  Empty implies the version of the containing resource list
    // For subresources, this may have a different value, for example: v1 (while inside a v1beta1 version of the core resource's group)".
    Version string `json:"version,omitempty" protobuf:"bytes,9,opt,name=version"`
    // kind is the kind for the resource (e.g. 'Foo' is the kind for a resource 'foo')
    Kind string `json:"kind" protobuf:"bytes,3,opt,name=kind"`
    // verbs is a list of supported kube verbs (this includes get, list, watch, create,
    // update, patch, delete, deletecollection, and proxy)
    Verbs Verbs `json:"verbs" protobuf:"bytes,4,opt,name=verbs"`
    // shortNames is a list of suggested short names of the resource.
    ShortNames []string `json:"shortNames,omitempty" protobuf:"bytes,5,rep,name=shortNames"`
    // categories is a list of the grouped resources this resource belongs to (e.g. 'all')
    Categories []string `json:"categories,omitempty" protobuf:"bytes,7,rep,name=categories"`
    // The hash value of the storage version, the version this resource is
    // converted to when written to the data store. Value must be treated
    // as opaque by clients. Only equality comparison on the value is valid.
    // This is an alpha feature and may change or be removed in the future.
    // The field is populated by the apiserver only if the
    // StorageVersionHash feature gate is enabled.
    // This field will remain optional even if it graduates.
    // +optional
    StorageVersionHash string `json:"storageVersionHash,omitempty" protobuf:"bytes,10,opt,name=storageVersionHash"`
}

资源版本分为：外部版本和内部版本

外部版本（External Version，例如：Deployment展示：apps/v1）
内部版本（Internal Version，Deployment展示未：apps/__internal）
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资源版本和内外部版本有关系吗？
有！有版本号的，属于外部版本（例如：apps/v1/deployments），没有版本号的，拥有runtime.APIVersionInternal（internal）标识的属于内部版本

资源对象分为：外部版本资源对象和内部版本资源对象

External Object 外部版本资源对象（Versioned Object，拥有资源版本的资源对象），用户通过yaml和json创建资源对象时，所使用的是外部资源对象，外部资源对象通过Alpha、Beta、Stable标识
Internal Object 内部版本资源对象，通过runtime.APIVersionInternal（_internal）标识，不对外暴露，内部使用，主要用于资源版本的转换，例如将v1beta1转为v1版本时候，顺序是先转为内部版本（internal），再转为v1版本，v1beta1→internal→v1

以pod资源为例： pod外部版本（External Version）

代码：vendor/k8s.io/api/core/v1/types.go (有版本号，有json tag和proto tag，用于序列化和反序列化操作)

type Pod struct {
    metav1.TypeMeta `json:",inline"`
    metav1.ObjectMeta `json:"metadata,omitempty" protobuf:"bytes,1,opt,name=metadata"`
tions.md#spec-and-status
    // +optional
    Spec PodSpec `json:"spec,omitempty" protobuf:"bytes,2,opt,name=spec"`
    Status PodStatus `json:"status,omitempty" protobuf:"bytes,3,opt,name=status"`
}

pod内部版本（Internal Version）定义：

pkg/apis/core/types.go (没有json tag)

type Pod struct {
    metav1.TypeMeta
    metav1.ObjectMeta
    Spec PodSpec
    Status PodStatus
}

Resource支持的两种资源

内置资源（Kubernetes Resource）和自定义资源(Custom Resource)

资源支持的8种操作方法

create、delete、deletecollection、get、list、patch、update、watch

资源的数据结构

GVR：Group Version Resource 资源组名称或者资源版本及资源名称
GV：Group Version 资源组以及资源版本
GVS：Group Versions 资源组内多个资源版本
GVK：Group VersionKind 资源组或者资源版本以及资源种类
GK：Group Kind 资源组或资源种类
GR：Group Resource 资源组或者资源

源码：k8s.io/apimachinery/pkg/runtime/schema/group_version.go

type GroupVersionResource struct {
    Group    string
    Version  string
    Resource string
}