Dynamic Kubelet Configuration

Alpha implementation of the Dynamic Kubelet Configuration feature.
See the proposal doc in #29459.

pkg/kubelet/kubeletconfig/util/codec/codec.go

@@ -0,0 +1,77 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package codec
+
+import (
+	"fmt"
+
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/kubernetes/pkg/api"
+	// ensure the core apis are installed
+	_ "k8s.io/kubernetes/pkg/api/install"
+	"k8s.io/kubernetes/pkg/apis/componentconfig"
+	// ensure the componentconfig api group is installed
+	_ "k8s.io/kubernetes/pkg/apis/componentconfig/install"
+	ccv1a1 "k8s.io/kubernetes/pkg/apis/componentconfig/v1alpha1"
+)
+
+// TODO(mtaufen): allow an encoder to be injected into checkpoint objects at creation time? (then we could ultimately instantiate only one encoder)
+
+// NewJSONEncoder generates a new runtime.Encoder that encodes objects to JSON
+func NewJSONEncoder(groupName string) (runtime.Encoder, error) {
+	// encode to json
+	mediaType := "application/json"
+	info, ok := runtime.SerializerInfoForMediaType(api.Codecs.SupportedMediaTypes(), mediaType)
+	if !ok {
+		return nil, fmt.Errorf("unsupported media type %q", mediaType)
+	}
+
+	versions := api.Registry.EnabledVersionsForGroup(groupName)
+	if len(versions) == 0 {
+		return nil, fmt.Errorf("no enabled versions for group %q", groupName)
+	}
+
+	// the "best" version supposedly comes first in the list returned from api.Registry.EnabledVersionsForGroup
+	return api.Codecs.EncoderForVersion(info.Serializer, versions[0]), nil
+}
+
+// DecodeKubeletConfiguration decodes an encoded (v1alpha1) KubeletConfiguration object to the internal type
+func DecodeKubeletConfiguration(data []byte) (*componentconfig.KubeletConfiguration, error) {
+	// TODO(mtaufen): when KubeletConfiguration moves out of componentconfig, will the UniversalDecoder still work?
+	// decode the object, note we use the external version scheme to decode, because users provide the external version
+	obj, err := runtime.Decode(api.Codecs.UniversalDecoder(ccv1a1.SchemeGroupVersion), data)
+	if err != nil {
+		return nil, fmt.Errorf("failed to decode, error: %v", err)
+	}
+
+	externalKC, ok := obj.(*ccv1a1.KubeletConfiguration)
+	if !ok {
+		return nil, fmt.Errorf("failed to cast object to KubeletConfiguration, object: %#v", obj)
+	}
+
+	// TODO(mtaufen): confirm whether api.Codecs.UniversalDecoder runs the defaulting, which would make this redundant
+	// run the defaulter on the decoded configuration before converting to internal type
+	api.Scheme.Default(externalKC)
+
+	// convert to internal type
+	internalKC := &componentconfig.KubeletConfiguration{}
+	err = api.Scheme.Convert(externalKC, internalKC, nil)
+	if err != nil {
+		return nil, err
+	}
+	return internalKC, nil
+}