#### 2.1.2 加载kubeconfig配置信息
**源码路径**：k8s.io\client-go\tools\clientcmd\loader.go
```go
func (rules *ClientConfigLoadingRules) Load() (*clientcmdapi.Config, error) {
......
kubeConfigFiles := []string{}
// Make sure a file we were explicitly told to use exists
if len(rules.ExplicitPath) > 0 {
if _, err := os.Stat(rules.ExplicitPath); os.IsNotExist(err) {
return nil, err
}
// 通过文件路径获取kubeconfig配置信息 -> rules.ExplicitPath
kubeConfigFiles = append(kubeConfigFiles, rules.ExplicitPath)
} else {
// 通过环境变量获取kubeconfig配置信息，rules.Precedence...可指定多个路径
kubeConfigFiles = append(kubeConfigFiles, rules.Precedence...)
}
kubeconfigs := []*clientcmdapi.Config{}
// read and cache the config files so that we only look at them once
for _, filename := range kubeConfigFiles {
......
// 读取数据并把读取的数据反序列化到Config对象中
config, err := LoadFromFile(filename)
......
}
.......
}
**源码路径**：k8s.io\client-go\tools\clientcmd\loader.go
```go
// Load takes a byte slice and deserializes the contents into Config object.
// Encapsulates deserialization without assuming the source is a file.
func Load(data []byte) (*clientcmdapi.Config, error) {
config := clientcmdapi.NewConfig()
......
// 执行反序列化操作
decoded, _, err := clientcmdlatest.Codec.Decode(data, &schema.GroupVersionKind{Version: clientcmdlatest.Version, Kind: "Config"}, config)
......
return decoded.(*clientcmdapi.Config), nil
}
2.1.3 合并多个kubeconfig配置信息
多个配置信息合并如图所示：
源码路径：k8s.io\client-go\tools\clientcmd\loader.go
func (rules *ClientConfigLoadingRules) Load() (*clientcmdapi.Config, error) {......// read and cache the config files so that we only look at them oncefor _, filename :=range kubeConfigFiles {...... config, err :=LoadFromFile(filename)......// first merge all of our maps mapConfig := clientcmdapi.NewConfig()for _, kubeconfig :=range kubeconfigs { mergo.MergeWithOverwrite(mapConfig, kubeconfig) }// merge all of the struct values in the reverse order so that priority is given correctly// errors are not added to the list the second time nonMapConfig := clientcmdapi.NewConfig()for i :=len(kubeconfigs) -1; i >=0; i-- { kubeconfig := kubeconfigs[i] mergo.MergeWithOverwrite(nonMapConfig, kubeconfig) }// since values are overwritten, but maps values are not, we can merge the non-map config on top of the map config and// get the values we expect. config := clientcmdapi.NewConfig() mergo.MergeWithOverwrite(config, mapConfig) mergo.MergeWithOverwrite(config, nonMapConfig)......}
func (r *Request) request(ctx context.Context, fn func(*http.Request, *http.Response)) error {......// Right now we make about ten retry attempts if we get a Retry-After response. retries :=0for { url := r.URL().String()//调用Go标准库net/http进行request构建 req, err := http.NewRequest(r.verb, url, r.body)if err !=nil {return err } req = req.WithContext(ctx) req.Header = r.headers......// Do发送request请求并接受resp resp, err := client.Do(req)......if err !=nil {// "Connection reset by peer" or "apiserver is shutting down" are usually a transient errors.// Thus in case of "GET" operations, we simply retry it.// We are not automatically retrying "write" operations, as// they are not idempotent.if r.verb !="GET" {return err }// For connection errors and apiserver shutdown errors retry.if net.IsConnectionReset(err) || net.IsProbableEOF(err) {// For the purpose of retry, we set the artificial "retry-after" response.// TODO: Should we clean the original response if it exists? resp =&http.Response{ StatusCode: http.StatusInternalServerError, Header: http.Header{"Retry-After": []string{"1"}}, Body: ioutil.NopCloser(bytes.NewReader([]byte{})), } } else {return err } } done :=func() bool {deferfunc() {......//Body.close()在defer函数中，保证函数退出时，对其进行关闭，防止内存溢出 resp.Body.Close() }()......//fn函数即为之前传入的transformResponse函数，将结果转为资源对象fn(req, resp)returntrue }()...... }}
DiscoveryClient是发现客户端，主要用于发现Kubenetes API Server所支持的资源组、资源版本、资源信息。 kubectl的api-versions和api-resources命令输出也是通过DiscoveryClient实现的。其同样是在RESTClient的基础上进行的封装。DiscoveryClient还可以将资源组、资源版本、资源信息等存储在本地，用于本地缓存，减轻对kubernetes api sever的访问压力，缓存信息默认存储在：~/.kube/cache和~/.kube/http-cache下。
func (d *DiscoveryClient) ServerGroups() (apiGroupList *metav1.APIGroupList, err error) {// Get the groupVersions exposed at /api// 在/api中获取groupVersions并将结构放于metav1.APIVersions v :=&metav1.APIVersions{} err = d.restClient.Get().AbsPath(d.LegacyPrefix).Do(context.TODO()).Into(v) apiGroup :=metav1.APIGroup{}if err ==nil&&len(v.Versions) !=0 { apiGroup =apiVersionsToAPIGroup(v) }if err !=nil&&!errors.IsNotFound(err) &&!errors.IsForbidden(err) {returnnil, err }// Get the groupVersions exposed at /apis// 在/apis中获取groupVersions并将结构放于metav1.APIGroupList apiGroupList =&metav1.APIGroupList{} err = d.restClient.Get().AbsPath("/apis").Do(context.TODO()).Into(apiGroupList)if err !=nil&&!errors.IsNotFound(err) &&!errors.IsForbidden(err) {returnnil, err }// to be compatible with a v1.0 server, if it's a 403 or 404, ignore and return whatever we got from /apiif err !=nil&& (errors.IsNotFound(err) || errors.IsForbidden(err)) { apiGroupList =&metav1.APIGroupList{} }// prepend the group retrieved from /api to the list if not empty//将api接口检索到的资源组信息合并到apiGroupList列表中iflen(v.Versions) !=0 { apiGroupList.Groups =append([]metav1.APIGroup{apiGroup}, apiGroupList.Groups...) }return apiGroupList, nil}
2.5.3 本地缓存的DiscoveryClient
DiscoveryClient可将资源相关信息存储在本地，默认每10分钟与kubernetes api server同步一次。 DiscoveryClient第一次获取资源组，资源版本，资源信息时，首先会查询本地缓存，如果数据不存在（没有命中）则请求Kubernetes API Server接口（回源），Cache将Kubernetes API Server响应的数据存储在本地一份并返回给DiscoveryClient。当下一次DiscoveryClient再次获取资源信息时，会将数据直接从本地缓存返回（命中）给DiscoveryClient。本地缓存的默认存储周期为10分钟。
func (d *CachedDiscoveryClient) ServerGroups() (*metav1.APIGroupList, error) { filename := filepath.Join(d.cacheDirectory, "servergroups.json")// 获取缓存Cache中的servergroups.json文件信息 cachedBytes, err := d.getCachedFile(filename)// don't fail on errors, we either don't have a file or won't be able to run the cached check. Either way we can fallback.if err ==nil { cachedGroups :=&metav1.APIGroupList{}if err := runtime.DecodeInto(scheme.Codecs.UniversalDecoder(), cachedBytes, cachedGroups); err ==nil { klog.V(10).Infof("returning cached discovery info from %v", filename)//将文件中的信息反序列化后转为cachedGroup对象并返回return cachedGroups, nil } }//如果没有命中返回，则从api-server中去获取信息 liveGroups, err := d.delegate.ServerGroups()......// 将最终的liveGroups回写到文件中if err := d.writeCachedFile(filename, liveGroups); err !=nil { klog.V(1).Infof("failed to write cache to %v due to %v", filename, err) }//返回liveGroupsreturn liveGroups, nil}
