参考文档：

  1. client-go官方库
  2. 从内部访问api-server
  3. 从外部访问api-server

集群配置管理

k8s的配置文件默认会存放在~/.kube/config中，其内容如下：
image.png

client-go中对于配置文件的管理可以简单概括为以下两点：

  • 加载配置文件
  • 合并配置文件（存疑。。。）

接下来分别从代码层面看一下。

加载配置文件

  1. func main() {
  2.         var kubeconfig *string
  4.         // 默认会从~/.kube/config路径下获取配置文件
  5.         if home := homeDir(); home != "" {
  6.                 kubeconfig = flag.String("kubeconfig", filepath.Join(home, ".kube", "config"), "(optional)absolute path to the kubeconfig file")
  7.         } else {
  8.                 kubeconfig = flag.String("kubeconfig", "", "absolute path to the kubeconfig file")
  9.         }
  11.         flag.Parse()
  13.         // 使用k8s.io/client-go/tools/clientcmd加载配置文件并生成config的对象
  14.         if config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig); err != nil {
  15.                 panic(err.Error())
  16.         }
  17. }

clientcmd.BuildConfigFromFlags加载配置文件后, 会生成一个Config的对象（具体信息）
这个对象中会包含如：apiserver地址、用户名、密码、token等信息。


进入到clientcmd.BuildConfigFromFlags查看其进行配置加载相关的代码：

进入到tools/clientcmd/client_config.go

  1. // BuildConfigFromFlags is a helper function that builds configs from a master
  2. // url or a kubeconfig filepath. These are passed in as command line flags for cluster
  3. // components. Warnings should reflect this usage. If neither masterUrl or kubeconfigPath
  4. // are passed in we fallback to inClusterConfig. If inClusterConfig fails, we fallback
  5. // to the default config.
  6. func BuildConfigFromFlags(masterUrl, kubeconfigPath string) (*restclient.Config, error) {
  7.     if kubeconfigPath == "" && masterUrl == "" {
  8.         klog.Warning("Neither --kubeconfig nor --master was specified.  Using the inClusterConfig.  This might not work.")
  9.         kubeconfig, err := restclient.InClusterConfig()
  10.         if err == nil {
  11.             return kubeconfig, nil
  12.         }
  13.         klog.Warning("error creating inClusterConfig, falling back to default config: ", err)
  14.     }
  15.     return NewNonInteractiveDeferredLoadingClientConfig(
  16.         &ClientConfigLoadingRules{ExplicitPath: kubeconfigPath},
  17.         &ConfigOverrides{ClusterInfo: clientcmdapi.Cluster{Server: masterUrl}}).ClientConfig()
  18. }

生成一个结构体：ClientConfigLoadingRules，这里面记录了当前传入的kubeconfig文件的位置。另外，在这个结构体中有一个变量load ClientConfigLoader，对于kubeconfig文件的管理，就是通过其中定义的[ClientConfigLoadingRules.Load()](https://github.com/kubernetes/client-go/blob/becbabb360023e1825a48b4db85f454e452ae249/tools/clientcmd/loader.go#L76)实现的。

  1. // ClientConfigLoadingRules is an ExplicitPath and string slice of specific locations that are used for merging together a Config
  2. // Callers can put the chain together however they want, but we'd recommend:
  3. // EnvVarPathFiles if set (a list of files if set) OR the HomeDirectoryPath
  4. // ExplicitPath is special, because if a user specifically requests a certain file be used and error is reported if this file is not present
  5. type ClientConfigLoadingRules struct {
  6.     ExplicitPath string
  7.     Precedence   []string
  9.     // MigrationRules is a map of destination files to source files.  If a destination file is not present, then the source file is checked.
  10.     // If the source file is present, then it is copied to the destination file BEFORE any further loading happens.
  11.     MigrationRules map[string]string
  13.     // DoNotResolvePaths indicates whether or not to resolve paths with respect to the originating files.  This is phrased as a negative so
  14.     // that a default object that doesn't set this will usually get the behavior it wants.
  15.     DoNotResolvePaths bool
  17.     // DefaultClientConfig is an optional field indicating what rules to use to calculate a default configuration.
  18.     // This should match the overrides passed in to ClientConfig loader.
  19.     DefaultClientConfig ClientConfig
  21.     // WarnIfAllMissing indicates whether the configuration files pointed by KUBECONFIG environment variable are present or not.
  22.     // In case of missing files, it warns the user about the missing files.
  23.     WarnIfAllMissing bool
  24. }

函数：

  1. // Load starts by running the MigrationRules and then
  2. // takes the loading rules and returns a Config object based on following rules.
  3. //   if the ExplicitPath, return the unmerged explicit file
  4. //   Otherwise, return a merged config based on the Precedence slice
  5. // A missing ExplicitPath file produces an error. Empty filenames or other missing files are ignored.
  6. // Read errors or files with non-deserializable content produce errors.
  7. // The first file to set a particular map key wins and map key's value is never changed.
  8. // BUT, if you set a struct value that is NOT contained inside of map, the value WILL be changed.
  9. // This results in some odd looking logic to merge in one direction, merge in the other, and then merge the two.
  10. // It also means that if two files specify a "red-user", only values from the first file's red-user are used.  Even
  11. // non-conflicting entries from the second file's "red-user" are discarded.
  12. // Relative paths inside of the .kubeconfig files are resolved against the .kubeconfig file's parent folder
  13. // and only absolute file paths are returned.
  14. func (rules *ClientConfigLoadingRules) Load() (*clientcmdapi.Config, error) {
  15.     if err := rules.Migrate(); err != nil {
  16.         return nil, err
  17.     }
  19.     errlist := []error{}
  20.     missingList := []string{}
  22.     kubeConfigFiles := []string{}
  24.     // Make sure a file we were explicitly told to use exists
  25.     if len(rules.ExplicitPath) > 0 {
  26.         if _, err := os.Stat(rules.ExplicitPath); os.IsNotExist(err) {
  27.             return nil, err
  28.         }
  29.         kubeConfigFiles = append(kubeConfigFiles, rules.ExplicitPath)
  31.     } else {
  32.         kubeConfigFiles = append(kubeConfigFiles, rules.Precedence...)
  33.     }
  35.     kubeconfigs := []*clientcmdapi.Config{}
  36.     // read and cache the config files so that we only look at them once
  37.     for _, filename := range kubeConfigFiles {
  38.         if len(filename) == 0 {
  39.             // no work to do
  40.             continue
  41.         }
  43.         config, err := LoadFromFile(filename)
  45.         if os.IsNotExist(err) {
  46.             // skip missing files
  47.             // Add to the missing list to produce a warning
  48.             missingList = append(missingList, filename)
  49.             continue
  50.         }
  52.         if err != nil {
  53.             errlist = append(errlist, fmt.Errorf("error loading config file \"%s\": %v", filename, err))
  54.             continue
  55.         }
  57.         kubeconfigs = append(kubeconfigs, config)
  58.     }
  60.     if rules.WarnIfAllMissing && len(missingList) > 0 && len(kubeconfigs) == 0 {
  61.         klog.Warningf("Config not found: %s", strings.Join(missingList, ", "))
  62.     }
  64.     // first merge all of our maps
  65.     mapConfig := clientcmdapi.NewConfig()
  67.     for _, kubeconfig := range kubeconfigs {
  68.         mergo.MergeWithOverwrite(mapConfig, kubeconfig)
  69.     }
  71.     // merge all of the struct values in the reverse order so that priority is given correctly
  72.     // errors are not added to the list the second time
  73.     nonMapConfig := clientcmdapi.NewConfig()
  74.     for i := len(kubeconfigs) - 1; i >= 0; i-- {
  75.         kubeconfig := kubeconfigs[i]
  76.         mergo.MergeWithOverwrite(nonMapConfig, kubeconfig)
  77.     }
  79.     // since values are overwritten, but maps values are not, we can merge the non-map config on top of the map config and
  80.     // get the values we expect.
  81.     config := clientcmdapi.NewConfig()
  82.     mergo.MergeWithOverwrite(config, mapConfig)
  83.     mergo.MergeWithOverwrite(config, nonMapConfig)
  85.     if rules.ResolvePaths() {
  86.         if err := ResolveLocalPaths(config); err != nil {
  87.             errlist = append(errlist, err)
  88.         }
  89.     }
  90.     return config, utilerrors.NewAggregate(errlist)
  91. }

合并配置文件

上面对kubeconfig完成加载后，下一步就需要对kubeconfig做合并处理。


代码位置:tools/clientcmd/loader.go

  2.     // since values are overwritten, but maps values are not, we can merge the non-map config on top of the map config and
  3.     // get the values we expect.
  4.     config := clientcmdapi.NewConfig()
  5.     mergo.Merge(config, mapConfig, mergo.WithOverride)
  6.     mergo.Merge(config, nonMapConfig, mergo.WithOverride)