helm源码分析之dependency update

发布一个k8s部署视频：https://edu.csdn.net/course/detail/26967

课程内容：各种k8s部署方式。包括minikube部署，kubeadm部署，kubeasz部署，rancher部署，k3s部署。包括开发测试环境部署k8s，和生产环境部署k8s。

腾讯课堂连接地址https://ke.qq.com/course/478827?taid=4373109931462251&tuin=ba64518

第二个视频发布  https://edu.csdn.net/course/detail/27109

腾讯课堂连接地址https://ke.qq.com/course/484107?tuin=ba64518

介绍主要的k8s资源的使用配置和命令。包括configmap，pod，service，replicaset，namespace，deployment，daemonset，ingress，pv，pvc，sc，role，rolebinding，clusterrole，clusterrolebinding，secret，serviceaccount，statefulset，job，cronjob，podDisruptionbudget，podSecurityPolicy,networkPolicy,resourceQuota，limitrange，endpoint，event，conponentstatus，node，apiservice，controllerRevision等。

第三个视频发布：https://edu.csdn.net/course/detail/27574

详细介绍helm命令，学习helm chart语法，编写helm chart。深入分析各项目源码，学习编写helm插件

第四个课程发布：https://edu.csdn.net/course/detail/28488

本课程将详细介绍k8s所有命令，以及命令的go源码分析，学习知其然，知其所以然

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func newDependencyUpdateCmd(out io.Writer) *cobra.Command {//创建dependecny update命令
	client := action.NewDependency()//初始化结构体

	cmd := &cobra.Command{//创建cobra命令
		Use:     "update CHART",
		Aliases: []string{"up"},
		Short:   "update charts/ based on the contents of Chart.yaml",
		Long:    dependencyUpDesc,
		Args:    require.MaximumNArgs(1),
		RunE: func(cmd *cobra.Command, args []string) error {
			chartpath := "."//设置chartpath为当前目录
			if len(args) > 0 {//如果参数大于0个，设置chart目录为第一个参数
				chartpath = filepath.Clean(args[0])
			}
			man := &downloader.Manager{//构造manager
				Out:              out,
				ChartPath:        chartpath,
				Keyring:          client.Keyring,
				SkipUpdate:       client.SkipRefresh,
				Getters:          getter.All(settings),
				RepositoryConfig: settings.RepositoryConfig,
				RepositoryCache:  settings.RepositoryCache,
				Debug:            settings.Debug,
			}
			if client.Verify {//判断是否verify
				man.Verify = downloader.VerifyAlways
			}
			return man.Update()//执行更新
		},
	}

	f := cmd.Flags()
	f.BoolVar(&client.Verify, "verify", false, "verify the packages against signatures")//verify选项
	f.StringVar(&client.Keyring, "keyring", defaultKeyring(), "keyring containing public keys")//keyring选项
	f.BoolVar(&client.SkipRefresh, "skip-refresh", false, "do not refresh the local repository cache")//skip-refresh选项

	return cmd
}

func (m *Manager) Update() error {//执行更新
	c, err := m.loadChartDir()//加载chart
	if err != nil {
		return err
	}

	// If no dependencies are found, we consider this a successful
	// completion.
	req := c.Metadata.Dependencies//获取chart的依赖
	if req == nil {
		return nil
	}

	// Check that all of the repos we're dependent on actually exist and
	// the repo index names.
	repoNames, err := m.resolveRepoNames(req)//解析仓库名称
	if err != nil {
		return err
	}

	// For each repo in the file, update the cached copy of that repo
	if !m.SkipUpdate {//如果不跳过update
		if err := m.UpdateRepositories(); err != nil {//更新仓库
			return err
		}
	}

	// Now we need to find out which version of a chart best satisfies the
	// dependencies in the Chart.yaml
	lock, err := m.resolve(req, repoNames)//解析依赖版本
	if err != nil {
		return err
	}

	// Now we need to fetch every package here into charts/
	if err := m.downloadAll(lock.Dependencies); err != nil {//下载依赖
		return err
	}

	// downloadAll might overwrite dependency version, recalculate lock digest
	newDigest, err := resolver.HashReq(req, lock.Dependencies)//计算依赖hash
	if err != nil {
		return err
	}
	lock.Digest = newDigest//设置hash

	// If the lock file hasn't changed, don't write a new one.
	oldLock := c.Lock
	if oldLock != nil && oldLock.Digest == lock.Digest {//如果新旧hash相同则直接返回
		return nil
	}

	// Finally, we need to write the lockfile.
	return writeLock(m.ChartPath, lock, c.Metadata.APIVersion == chart.APIVersionV1)//写依赖lock文件
}

//写依赖lock文件
func writeLock(chartpath string, lock *chart.Lock, legacyLockfile bool) error {
	data, err := yaml.Marshal(lock)//把lock文件内容转成yaml
	if err != nil {
		return err
	}
	lockfileName := "Chart.lock"//设置lock文件名称
	if legacyLockfile {//如果是老版本，设置lock文件名称
		lockfileName = "requirements.lock"
	}
	dest := filepath.Join(chartpath, lockfileName)//获取完成文件名称
	return ioutil.WriteFile(dest, data, 0644)//写数据到文件
}