1、什麼是Docker？

Docker Linux 平臺上的一款輕量級虛擬化容器的管理引擎。在全球範圍內， Docker 還是一個開源專案，整個專案基於 Go 語言開發，程式碼託管於 GitHub 網站上，並遵從 Apache 2.0 協議。目前， Docker 可以幫助使用者在容器內部快速自動化部署應用，並利用 Linux 核心特性名稱空間( namespaces) 及控制組( cgroups) 等為容器提供隔離的執行環境。Docker 藉助作業系統層的虛擬化實現資源的隔離，因此 Docker 容器在執行時與虛擬機器 (VM) 的執行有很大的區別， Docker 容器與宿主機共享同一個作業系統，不會有額外的作業系統開銷。

2、Docker總體架構圖

檢視架構圖詳解，請參考：https://www.infoq.cn/article/docker-source-code-analysis-part1

3、背景：

瞭解Docker原始碼解析Dockerfile的流程，瞭解docker build以及docker run 在client、daemon和engine端的處理。

4、 原始碼基於Docker-ce17.09.

5、原始碼：

Docker Client 是Docker 架構中使用者與 Docker Daemon 建立通訊的客戶端。從main（）函式開始，位置點選。

5.1、流程：（截圖於博友，自己作圖太麻煩，跟17.09有點差別，自己對比）

5.2、原始碼分析：

docker client的入口函式main，在main中處理傳入的引數，並把引數轉化為cobra的command型別，最後通過cobra呼叫相應的方法。

5.2.1、func AddCommands（）函式

// AddCommands adds all the commands from cli/command to the root command
func AddCommands(cmd *cobra.Command, dockerCli *command.DockerCli) {
	cmd.AddCommand(
		// checkpoint
		checkpoint.NewCheckpointCommand(dockerCli),

		// config
		config.NewConfigCommand(dockerCli),

		// container
		container.NewContainerCommand(dockerCli),
               //新增子命令run及其選項
		container.NewRunCommand(dockerCli),

		// image
		image.NewImageCommand(dockerCli),
		image.NewBuildCommand(dockerCli),

		// registry
		registry.NewLoginCommand(dockerCli),
		registry.NewLogoutCommand(dockerCli),
		registry.NewSearchCommand(dockerCli),

		// secret
		secret.NewSecretCommand(dockerCli),

		// service
		service.NewServiceCommand(dockerCli),

		// system
		system.NewSystemCommand(dockerCli),
		system.NewVersionCommand(dockerCli),

               ……………………
	)

}
 

5.2.2、func NewRunCommand（）函式

// NewRunCommand create a new `docker run` command
func NewRunCommand(dockerCli *command.DockerCli) *cobra.Command {
	var opts runOptions
	var copts *containerOptions

	cmd := &cobra.Command{
		Use:   "run [OPTIONS] IMAGE [COMMAND] [ARG...]",
		Short: "Run a command in a new container",
		Args:  cli.RequiresMinArgs(1),
		RunE: func(cmd *cobra.Command, args []string) error {
			copts.Image = args[0]
			if len(args) > 1 {
				copts.Args = args[1:]
			}
                        //run對應的客戶端方法
			return runRun(dockerCli, cmd.Flags(), &opts, copts)
		},
	}

	flags := cmd.Flags()
	flags.SetInterspersed(false)

	// These are flags not stored in Config/HostConfig
	flags.BoolVarP(&opts.detach, "detach", "d", false, "Run container in background and print container ID")
	flags.BoolVar(&opts.sigProxy, "sig-proxy", true, "Proxy received signals to the process")
	flags.StringVar(&opts.name, "name", "", "Assign a name to the container")
	flags.StringVar(&opts.detachKeys, "detach-keys", "", "Override the key sequence for detaching a container")

	// Add an explicit help that doesn't have a `-h` to prevent the conflict
	// with hostname
	flags.Bool("help", false, "Print usage")

	command.AddTrustVerificationFlags(flags)
	copts = addFlags(flags)
	return cmd
}

5.2.3、func runRun（）函式

func runRun(dockerCli *command.DockerCli, flags *pflag.FlagSet, ropts *runOptions, copts *containerOptions) error {
        //得到代理配置	// ConfigFile ~/.docker/config.json file info
        proxyConfig := dockerCli.ConfigFile().ParseProxyConfig(dockerCli.Client().DaemonHost(), copts.env.GetAll())
	newEnv := []string{}
	for k, v := range proxyConfig {
		if v == nil {
			newEnv = append(newEnv, k)
		} else {
			newEnv = append(newEnv, fmt.Sprintf("%s=%s", k, *v))
		}
	}
	copts.env = *opts.NewListOptsRef(&newEnv, nil)
	containerConfig, err := parse(flags, copts)
	// just in case the parse does not exit
	if err != nil {
		reportError(dockerCli.Err(), "run", err.Error(), true)
		return cli.StatusError{StatusCode: 125}
	}
         //呼叫runContainer
	return runContainer(dockerCli, ropts, copts, containerConfig)
}

5.2.4、func runContainer（）函式

func runContainer(dockerCli *command.DockerCli, opts *runOptions, copts *containerOptions, containerConfig *containerConfig) error {
	config := containerConfig.Config
	hostConfig := containerConfig.HostConfig
	stdout, stderr := dockerCli.Out(), dockerCli.Err()
	//例項化一個客戶端，用於傳送run命令請求
	client := dockerCli.Client()

	// TODO: pass this as an argument
	cmdPath := "run"

	warnOnOomKillDisable(*hostConfig, stderr)
	warnOnLocalhostDNS(*hostConfig, stderr)

	config.ArgsEscaped = false

	if !opts.detach {
		if err := dockerCli.In().CheckTty(config.AttachStdin, config.Tty); err != nil {
			return err
		}
	} else {

         ……省略
	ctx, cancelFun := context.WithCancel(context.Background())
	//client向engine傳送create容器請求
	createResponse, err := createContainer(ctx, dockerCli, containerConfig, opts.name)
         ……省略
	//start the container
	////client向engine傳送start容器請求
	if err := client.ContainerStart(ctx, createResponse.ID, types.ContainerStartOptions{}); err != nil {
		
}

5.2.5、func createContainer（）函式

func createContainer(ctx context.Context, dockerCli command.Cli, containerConfig *containerConfig, name string) (*container.ContainerCreateCreatedBody, error) {
	config := containerConfig.Config
	hostConfig := containerConfig.HostConfig
	networkingConfig := containerConfig.NetworkingConfig
	stderr := dockerCli.Err()

	var (
		trustedRef reference.Canonical
		namedRef   reference.Named
	)

	containerIDFile, err := newCIDFile(hostConfig.ContainerIDFile)
	if err != nil {
		return nil, err
	}
	defer containerIDFile.Close()

	ref, err := reference.ParseAnyReference(config.Image)
	if err != nil {
		return nil, err
	}
	if named, ok := ref.(reference.Named); ok {
		namedRef = reference.TagNameOnly(named)

		if taggedRef, ok := namedRef.(reference.NamedTagged); ok && command.IsTrusted() {
			var err error
			trustedRef, err = image.TrustedReference(ctx, dockerCli, taggedRef, nil)
			if err != nil {
				return nil, err
			}
			config.Image = reference.FamiliarString(trustedRef)
		}
	}

	//create the container
	response, err := dockerCli.Client().ContainerCreate(ctx, config, hostConfig, networkingConfig, name)

	//if image not found try to pull it
	if err != nil {
		if apiclient.IsErrImageNotFound(err) && namedRef != nil {
			fmt.Fprintf(stderr, "Unable to find image '%s' locally\n", reference.FamiliarString(namedRef))

			// we don't want to write to stdout anything apart from container.ID
			if err := pullImage(ctx, dockerCli, config.Image, stderr); err != nil {
				return nil, err
			}
			if taggedRef, ok := namedRef.(reference.NamedTagged); ok && trustedRef != nil {
				if err := image.TagTrusted(ctx, dockerCli, trustedRef, taggedRef); err != nil {
					return nil, err
				}
			}
			// Retry
			var retryErr error
			response, retryErr = dockerCli.Client().ContainerCreate(ctx, config, hostConfig, networkingConfig, name)
			if retryErr != nil {
				return nil, retryErr
			}
		} else {
			return nil, err
		}
	}

	for _, warning := range response.Warnings {
		fmt.Fprintf(stderr, "WARNING: %s\n", warning)
	}
	err = containerIDFile.Write(response.ID)
	return &response, err
}

5.2.6、ContainerCreate()

// ContainerAPIClient defines API client methods for the containers
type ContainerAPIClient interface {
	//API create方法
        ContainerCreate(ctx context.Context, config *container.Config, hostConfig *container.HostConfig, networkingConfig *network.NetworkingConfig, containerName string) (container.ContainerCreateCreatedBody, error)
	
        //API start方法
	ContainerStart(ctx context.Context, container string, options types.ContainerStartOptions) error
	
}

//ContainerCreate基於給定配置建立新容器。 它可以與名稱相關聯，但不是強制性的。
func (cli *Client) ContainerCreate(ctx context.Context, config *container.Config, hostConfig *container.HostConfig, networkingConfig *network.NetworkingConfig, containerName string) (container.ContainerCreateCreatedBody, error) {
	var response container.ContainerCreateCreatedBody

	if err := cli.NewVersionError("1.25", "stop timeout"); config != nil && config.StopTimeout != nil && err != nil {
		return response, err
	}

	// When using API 1.24 and under, the client is responsible for removing the container
	if hostConfig != nil && versions.LessThan(cli.ClientVersion(), "1.25") {
		hostConfig.AutoRemove = false
	}

	query := url.Values{}
	if containerName != "" {
		query.Set("name", containerName)
	}

	body := configWrapper{
		Config:           config,
		HostConfig:       hostConfig,
		NetworkingConfig: networkingConfig,
	}
	//傳送post請求
	serverResp, err := cli.post(ctx, "/containers/create", query, body, nil)
	if err != nil {
		if serverResp.statusCode == 404 && strings.Contains(err.Error(), "No such image") {
			return response, imageNotFoundError{config.Image}
		}
		return response, err
	}

	err = json.NewDecoder(serverResp.body).Decode(&response)
	ensureReaderClosed(serverResp)
	return response, err
}

5.3、總結

在第5.2.4節上，startContainer（）函式就不介紹了，跟createContainer類似，後面有需要，咱再分析。

下一篇章就分析docker run命令在daemon中的處理流程了。

參考：

           https://www.infoq.cn/article/docker-source-code-analysis-part1

https://guanjunjian.github.io/2017/09/26/study-1-docker-1-client-excuting-flow-for-run/

https://blog.csdn.net/warrior_0319/article/details/79931987

《docker原始碼分析》

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