Kubernetes 系列 - 9. apiserver（六、scheme）

9. apiserver（六、scheme）

9.1 scheme设计

apiserver从设计上分为api和server两部分，将资源处理解耦出来，其中api包含资源相关的信息，如：资源定义、gvk映射、版本转换等，而server主要负责通用的请求处理流程，如路由、鉴权、超时处理等。

9.2 scheme字段

type Scheme struct {
    // gvkToType allows one to figure out the go type of an object with
    // the given version and name.
    gvkToType map[schema.GroupVersionKind]reflect.Type

    // typeToGVK allows one to find metadata for a given go object.
    // The reflect.Type we index by should *not* be a pointer.
    typeToGVK map[reflect.Type][]schema.GroupVersionKind

    // unversionedTypes are transformed without conversion in ConvertToVersion.
    unversionedTypes map[reflect.Type]schema.GroupVersionKind

    // unversionedKinds are the names of kinds that can be created in the context of any group
    // or version
    // TODO: resolve the status of unversioned types.
    unversionedKinds map[string]reflect.Type

    // Map from version and resource to the corresponding func to convert
    // resource field labels in that version to internal version.
    fieldLabelConversionFuncs map[schema.GroupVersionKind]FieldLabelConversionFunc

    // defaulterFuncs is a map to funcs to be called with an object to provide defaulting
    // the provided object must be a pointer.
    defaulterFuncs map[reflect.Type]func(interface{})

    // converter stores all registered conversion functions. It also has
    // default converting behavior.
    converter *conversion.Converter

    // versionPriority is a map of groups to ordered lists of versions for those groups indicating the
    // default priorities of these versions as registered in the scheme
    versionPriority map[string][]string

    // observedVersions keeps track of the order we've seen versions during type registration
    observedVersions []schema.GroupVersion

    // schemeName is the name of this scheme.  If you don't specify a name, the stack of the NewScheme caller will be used.
    // This is useful for error reporting to indicate the origin of the scheme.
    schemeName string
}

以下是对重要字段的解释：

字段	用途
gvkToType	利用gvk信息构建实例
typeToGvk	提取实例的gvk信息
converter	版本转换函数，在内外版本进行转换
defaulterFuncs	默认值设置函数，对用户没有设置的字段进行赋值
versionPriority	存储版本优先级

9.3 导入流程

apiserver导入scheme使用了go的init机制，同时采用了解耦的思想将具体的包与apiserver解除绑定，引入import_known_versions和intsall避免增加版本时修改apiserver。

具体的导入代码：

var (
    localSchemeBuilder = &admissionv1beta1.SchemeBuilder
    // AddToScheme is a common registration function for mapping packaged scoped group & version keys to a scheme
    AddToScheme = localSchemeBuilder.AddToScheme
)

func init() {
    // We only register manually written functions here. The registration of the
    // generated functions takes place in the generated files. The separation
    // makes the code compile even when the generated files are missing.
    localSchemeBuilder.Register(RegisterDefaults)
}

实际导入的时候用了builder模式，使用SchemeBuilder组装需要应用的函数，调用AddToScheme最终完成注册：

NewSchemeBuilder -> Register -> Register -> ... -> AddToScheme

实际用的时候，也有将需要应用的函数在NewSchemeBuilder就传入了，不再Register的情况。