【kubernetes/k8s概念】kubernetes scheme原理分析

    github: k8s.io/apimachinery/pkg/runtime/schema

1. Scheme 结构体

     Scheme 定义了资源序列化和反序列化的方法以及资源类型和版本的对应关系；这里我们可以理解成一张纪录表。定义在 k8s.io/apimachinery/pkg/runtime/scheme.go 中。需要关注的 gvkToTypeype 和 typeToGVK 字段

// Scheme defines methods for serializing and deserializing API objects, a type
// registry for converting group, version, and kind information to and from Go
// schemas, and mappings between Go schemas of different versions. A scheme is the
// foundation for a versioned API and versioned configuration over time.
//
// In a Scheme, a Type is a particular Go struct, a Version is a point-in-time
// identifier for a particular representation of that Type (typically backwards
// compatible), a Kind is the unique name for that Type within the Version, and a
// Group identifies a set of Versions, Kinds, and Types that evolve over time. An
// Unversioned Type is one that is not yet formally bound to a type and is promised
// to be backwards compatible (effectively a "v1" of a Type that does not expect
// to break in the future).
//
// Schemes are not expected to change at runtime and are only threadsafe after
// registration is complete.
type Scheme struct {
	// versionMap allows one to figure out the go type of an object with
	// the given version and name.
	gvkToType map[schema.GroupVersionKind]reflect.Type

	// typeToGroupVersion 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 an array of interfaces 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
}

   

    当和 API Server 通信的时候能够处理新的 types 类型就需要知道有新的types类型，AddToScheme 会利用到反射，新定义的 types 类型的结构体的命名必须和自定义的 Kind 的命名一致，否则找不到对应的kind

var (
	// SchemeGroupVersion is group version used to register these objects
	SchemeGroupVersion = schema.GroupVersion{Group: "apps.krome.io", Version: "v1"}

	// SchemeBuilder is used to add go types to the GroupVersionKind scheme
	// SchemeBuilder = &scheme.Builder{GroupVersion: SchemeGroupVersion}
	SchemeBuilder = runtime.NewSchemeBuilder(addKnownTypes)

	// AddToScheme is a global function that registers this API group & version to a scheme
	AddToScheme = SchemeBuilder.AddToScheme
)

2. SchemeBuilder 

    资源向Scheme注册的接口函数 SchemeFunc---AddToScheme，SchemeBuilder 实际上是一个函数数组， AddToScheme 函数就是将包含的处理函数依次应用到 Scheme 上

// SchemeBuilder collects functions that add things to a scheme. It's to allow
// code to compile without explicitly referencing generated types. You should
// declare one in each package that will have generated deep copy or conversion
// functions.
type SchemeBuilder []func(*Scheme) error

// AddToScheme applies all the stored functions to the scheme. A non-nil error
// indicates that one function failed and the attempt was abandoned.
func (sb *SchemeBuilder) AddToScheme(s *Scheme) error {
	for _, f := range *sb {
		if err := f(s); err != nil {
			return err
		}
	}
	return nil
}

    自定义 addKnownTypes 函数，注册 group-version，对应的资源对象

func addKnownTypes(scheme *runtime.Scheme) error {
	scheme.AddKnownTypes(
		SchemeGroupVersion,
		&StatefulSet{},
		&StatefulSetList{},
	)

	// register the type in the scheme
	metav1.AddToGroupVersion(scheme, SchemeGroupVersion)
	return nil
}

    2.1  scheme 的 AddKnowTypes 方法

     定义在 k8s.io/apimachinery/pkg/runtime/scheme.go 中，addObservedVersion 函数添加到 Scheme 的 observedVersions 字段中，是个 []schema.GroupVersion 结构，AddKnownTypeWIthName 函数添加到 Scheme 的 typeToGVK 和 gvkToType 

// AddKnownTypes registers all types passed in 'types' as being members of version 'version'.
// All objects passed to types should be pointers to structs. The name that go reports for
// the struct becomes the "kind" field when encoding. Version may not be empty - use the
// APIVersionInternal constant if you have a type that does not have a formal version.
func (s *Scheme) AddKnownTypes(gv schema.GroupVersion, types ...Object) {
	s.addObservedVersion(gv)
	for _, obj := range types {
		t := reflect.TypeOf(obj)
		if t.Kind() != reflect.Ptr {
			panic("All types must be pointers to structs.")
		}
		t = t.Elem()
		s.AddKnownTypeWithName(gv.WithKind(t.Name()), obj)
	}
}

3. 使用 SchemeBuilder 

    在 defaults.go 文件添加函数，RegisterDefaults 是自动生成，产生的文件 zz_generated.defaults.go，需要的条件是在自定义的资源添加 tag，// +k8s:defaulter-gen=true，生成需要使用，修改generate-groups.sh脚本，添加对应的模块，或者直接执行命令

// defaulter-gen --input-dirs krome/pkg/apis/apps/v1 --input-dirs krome/pkg/apis/apps
// -o $GOPATH/src --go-header-file boilerplate.go.txt
// -O zz_generated.defaults
// --extra-peer-dirs= k8s.io/apimachinery/pkg/apis/meta/v1,k8s.io/apimachinery/pkg/conversion,k8s.io/apimachinery/pkg/runtime

func addDefaultingFuncs(scheme *runtime.Scheme) error {
	return RegisterDefaults(scheme)
}

    3.1 RegisterDefaults 函数

      生成的为 nil 未实现任何方法，可以添加自己定义的逻辑，这里添加的 StatefulSet StatefulSetList，设置一些默认的字段值，防止出现空指针问题

// RegisterDefaults adds defaulters functions to the given scheme.
// Public to allow building arbitrary schemes.
// All generated defaulters are covering - they call all nested defaulters.
func RegisterDefaults(scheme *runtime.Scheme) error {
	scheme.AddTypeDefaultingFunc(&StatefulSet{}, func(obj interface{}) { SetObjectDefaults_StatefulSet(obj.(*StatefulSet)) })
	scheme.AddTypeDefaultingFunc(&StatefulSetList{}, func(obj interface{}) { SetObjectDefaults_StatefulSetList(obj.(*StatefulSetList)) })

	return nil
}