Convert资源版本转换器

Kubernetes允许同一资源的不同版本进行准换，进行转换之前，需要查看资源对象支持的资源组和资源版本：

  1. $ kubectl version
  2. Client Version: version.Info{
  3.   Major:"1", 
  4.   Minor:"16+", 
  5.   GitVersion:"v1.16.6-beta.0", 
  6.   GitCommit:"e7f962ba86f4ce7033828210ca3556393c377bcc", 
  7.   GitTreeState:"clean", 
  8.   BuildDate:"2020-01-15T08:26:26Z", 
  9.   GoVersion:"go1.13.5", 
  10.   Compiler:"gc", 
  11.   Platform:"darwin/amd64"
  12. }
  13. Server Version: version.Info{
  14.   Major:"1", 
  15.   Minor:"19", 
  16.   GitVersion:"v1.19.2", 
  17.   GitCommit:"f5743093fd1c663cb0cbc89748f730662345d44d", 
  18.   GitTreeState:"clean", 
  19.   BuildDate:"2020-09-16T13:32:58Z", 
  20.   GoVersion:"go1.15", 
  21.   Compiler:"gc", 
  22.   Platform:"linux/amd64"
  23. }
  25. $ kubectl api-versions | grep autoscaling
  26. autoscaling/v1
  27. autoscaling/v2beta1
  28. autoscaling/v2beta2
  30. $ kubectl api-resources --api-group=autoscaling
  31. NAME                       SHORTNAMES   APIGROUP      NAMESPACED   KIND
  32. horizontalpodautoscalers   hpa          autoscaling   true         HorizontalPodAutoscaler

通过kubectl version、kubectl api-versions、kubectl api-resources查看当前版本Kubernetes集群中的autoscaling资源组下的资源版本，以及Kind。可以发现v1.19.2集群中的autoscaling资源组有三个资源版本，分别为v1/v2beta1/v2beta2。并且autoscaling资源组下拥有HorizontalPodAutoscaler资源对象。
比如将对象HorizontalPodAutoscaler版本的v1转换为v2beta1：

  1. # v1版本的HPA
  2. apiVersion: autoscaling/v1
  3. kind: HorizontalPodAutoscaler
  4. metadata:
  5.   labels:
  6.     hpa: my-temp-hpa
  7.   name: my-temp-hpa
  8. spec:
  9.   maxReplicas: 10
  10.   minReplicas: 1
  11.   scaleTargetRef:
  12.     apiVersion: apps/v1
  13.     kind: Deployment
  14.     name: my-temp
  15.   targetCPUUtilizationPercentage: 20

通过一下命令将其转换为v2beta1版本

  1. $ kubectl convert -f hpa_v1_v1beta1.yaml --output-version=autoscaling/v2beta1
  2. kubectl convert is DEPRECATED and will be removed in a future version.
  3. In order to convert, kubectl apply the object to the cluster, then kubectl get at the desired version.
  4. apiVersion: autoscaling/v2beta1
  5. kind: HorizontalPodAutoscaler
  6. metadata:
  7.   creationTimestamp: null
  8.   labels:
  9.     hpa: my-temp-hpa
  10.   name: my-temp-hpa
  11. spec:
  12.   maxReplicas: 10
  13.   metrics:
  14.   - resource:
  15.       name: cpu
  16.       targetAverageUtilization: 20
  17.     type: Resource
  18.   minReplicas: 1
  19.   scaleTargetRef:
  20.     apiVersion: apps/v1
  21.     kind: Deployment
  22.     name: my-temp
  23. status:
  24.   conditions: null
  25.   currentMetrics: null
  26.   currentReplicas: 0
  27.   desiredReplicas: 0

为了解决多个版本之间的转换问题，Kubernetes通过内部版本__internal进行多个外部版本之间的转换。

Convert转换器数据结构

Convert转换器数据结构主要存放转换函数（即Conversion Funs）。Convert数据结构如下：
代码路径：vendor/k8s.io/apimachinery/pkg/conversion/convert.go

  1. // Converter knows how to convert one type to another.
  2. type Converter struct {
  3.     // Map from the conversion pair to a function which can
  4.     // do the conversion.
  5.     conversionFuncs          ConversionFuncs // 默认的转换函数，一般定义在资源目录下conversion.go中
  6.     generatedConversionFuncs ConversionFuncs // 自动生成的转换函数，一般定义在资源目录下zz_generated.conversion.go目录中
  8.     // Set of conversions that should be treated as a no-op
  9.     ignoredConversions        map[typePair]struct{} // 若资源对象注册到此字段，则忽略此资源对象的转换操作
  10.     ignoredUntypedConversions map[typePair]struct{}
  12.     // nameFunc is called to retrieve the name of a type; this name is used for the
  13.     // purpose of deciding whether two types match or not (i.e., will we attempt to
  14.     // do a conversion). The default returns the go type name.
  15.     // // 在转换过程中获取资源种类的名称，该函数被定义在vendor/k8s.io/apimachinery/pkg/runtime/scheme.go
  16.     nameFunc func(t reflect.Type) string 
  17. }

Convert转换器数据结构中存放的转换函数（即Conversion Funcs）可以分为两类，分别为默认的转换函数（即ConversionFuncs）字段和自动生成的转换函数（即generatedConversionFuncs）字段。它们都通过ConversionFuncs来管理，代码示例如下：

  1. type ConversionFuncs struct {
  2.     untyped map[typePair]ConversionFunc
  3. }
  5. type typePair struct {
  6.     source reflect.Type
  7.     dest   reflect.Type
  8. }
  10. // ConversionFunc converts the object a into the object b, reusing arrays or objects
  11. // or pointers if necessary. It should return an error if the object cannot be converted
  12. // or if some data is invalid. If you do not wish a and b to share fields or nested
  13. // objects, you must copy a before calling this function.
  14. type ConversionFunc func(a, b interface{}, scope Scope) error
  16. // scope contains information about an ongoing conversion.
  17. type scope struct {
  18.     converter *Converter
  19.     meta      *Meta
  20. }

ConversionFunc类型函数（即Type Function）定义了转换函数实现的结构，将资源a转换为资源b。a定义了源资源类型，b定义了目标资源类型。scope定义了多次转换机制（即递归调用转换函数）。

Converter注册转换函数

Converter转换函数需要注册才能在Kubernetes内部使用，Kubernetes支持一下注册函数：
代码路径: vendor/k8s.io/apimachinery/pkg/runtime/scheme.go

  1. // AddIgnoredConversionType identifies a pair of types that should be skipped by
  2. // conversion (because the data inside them is explicitly dropped during
  3. // conversion).
  4. func (s *Scheme) AddIgnoredConversionType(from, to interface{}) error {
  5.     return s.converter.RegisterIgnoredConversion(from, to)
  6. }
  8. // AddConversionFunc registers a function that converts between a and b by passing objects of those
  9. // types to the provided function. The function *must* accept objects of a and b - this machinery will not enforce
  10. // any other guarantee.
  11. func (s *Scheme) AddConversionFunc(a, b interface{}, fn conversion.ConversionFunc) error {
  12.     return s.converter.RegisterUntypedConversionFunc(a, b, fn)
  13. }
  15. // AddGeneratedConversionFunc registers a function that converts between a and b by passing objects of those
  16. // types to the provided function. The function *must* accept objects of a and b - this machinery will not enforce
  17. // any other guarantee.
  18. func (s *Scheme) AddGeneratedConversionFunc(a, b interface{}, fn conversion.ConversionFunc) error {
  19.     return s.converter.RegisterGeneratedUntypedConversionFunc(a, b, fn)
  20. }
  22. // AddFieldLabelConversionFunc adds a conversion function to convert field selectors
  23. // of the given kind from the given version to internal version representation.
  24. func (s *Scheme) AddFieldLabelConversionFunc(gvk schema.GroupVersionKind, conversionFunc FieldLabelConversionFunc) error {
  25.     s.fieldLabelConversionFuncs[gvk] = conversionFunc
  26.     return nil
  27. }
  • AddIgnoredConversionType：注册忽略的资源类型，不会执行转换操作
  • AddConversionFunc：注册单个ConvertionFunc转换函数
  • AddGeneratedConversionFunc：注册自动生成的转换函数
  • AddFieldLabelConversionFunc：注册字段标签（FieldLabel）的转换函数