【containerd 1.0 源码分析】containerd-shime 启动流程分析

命令：

shim for container lifecycle and reconnection




USAGE:
   containerd-shim [global options] command [command options] [arguments...]


VERSION:
   v1.0.0-alpha3.m


COMMANDS:
     help, h  Shows a list of commands or help for one command


GLOBAL OPTIONS:
   --debug                      enable debug output in logs
   --namespace value, -n value  namespace that owns the task
   --socket value, -s value     abstract socket path to serve on
   --address value, -a value    grpc address back to containerd
   --help, -h                   show help
   --version, -v                print the version

一. containerd-shim main 函数

   1.1 入口目录为 cmd/containerd/main.go 中 main 函数，NewApp 使用了第三方一个命令行设置，设置名字，以及命令行启动参数，子命令等

app := cli.NewApp()app.Name = "containerd-shim"app.Version = version.Versionapp.Usage = usageapp.Flags = []cli.Flag{       cli.BoolFlag{              Name:  "debug",              Usage: "enable debug output in logs",       },       cli.StringFlag{              Name:  "namespace,n",              Usage: "namespace that owns the task",       },       cli.StringFlag{              Name:  "socket,s",              Usage: "abstract socket path to serve on",       },       cli.StringFlag{              Name:  "address,a",              Usage: "grpc address back to containerd",       },}app.Before = func(context *cli.Context) error {       if context.GlobalBool("debug") {              logrus.SetLevel(logrus.DebugLevel)       }       return nil}

   1.2 app.Action 主要是建立 GRPC 服务，以及创建 shim 服务

app.Action = func(context *cli.Context) error {       // start handling signals as soon as possible so that things are properly reaped       // or if runtime exits before we hit the handler       signals, err := setupSignals()       if err != nil {              return err       }       path, err := os.Getwd()       if err != nil {              return err       }       server := grpc.NewServer()       e, err := connectEvents(context.GlobalString("address"))       if err != nil {              return err       }       sv, err := shim.NewService(              path,              context.GlobalString("namespace"),              &remoteEventsPublisher{client: e},       )       if err != nil {              return err       }       logrus.Debug("registering grpc server")       shimapi.RegisterShimServer(server, sv)       socket := context.GlobalString("socket")       if err := serve(server, socket); err != nil {              return err       }       return handleSignals(signals, server)}

   1.3 NewService 如下

// NewService returns a new shim service that can be used via GRPCfunc NewService(path, namespace string, publisher events.Publisher) (*Service, error) {       if namespace == "" {              return nil, fmt.Errorf("shim namespace cannot be empty")       }       context := namespaces.WithNamespace(context.Background(), namespace)       s := &Service{              path:      path,              processes: make(map[string]process),              events:    make(chan interface{}, 4096),              namespace: namespace,              context:   context,       }       if err := s.initPlatform(); err != nil {              return nil, errors.Wrap(err, "failed to initialized platform behavior")       }       go s.forward(publisher)       return s, nil}

   1.4 serve 如果没有指定 --socket 则从父继承过来

// serve serves the grpc API over a unix socket at the provided path// this function does not blockfunc serve(server *grpc.Server, path string) error {       var (              l   net.Listener              err error       )       if path == "" {              l, err = net.FileListener(os.NewFile(3, "socket"))              path = "[inherited from parent]"       } else {              l, err = net.Listen("unix", "\x00"+path)       }       if err != nil {              return err       }       logrus.WithField("socket", path).Debug("serving api on unix socket")       go func() {              defer l.Close()              if err := server.Serve(l); err != nil &&                     !strings.Contains(err.Error(), "use of closed network connection") {                     logrus.WithError(err).Fatal("containerd-shim: GRPC server failure")              }       }()       return nil}