容器生命周期钩子(Container Lifecycle Hooks)监听容器生命周期的特定事件,并在事件发生时执行已注册的回调函数。
钩子函数能够感知自身生命周期中的事件,并在相应的时刻到来时运行用户指定的程序代码。
kubernetes在主容器的启动之后和停止之前提供了两个钩子函数:
钩子的回调函数支持两种方式定义动作,下面以 postStart 为例讲解,preStop 定义方式与其一致:
在容器中执行指定的命令。如果命令退出时返回码为0,判定为执行成功。
示例:
lifecycle: postStart: exec: command: - cat - /var/lib/redis.conf
对容器中的指定端点执行HTTP GET请求,如果响应的状态码大于等于200且小于400,判定为执行成功。
httpGet模式支持以下配置参数:
Host:HTTP请求主机地址,不设置时默认为Pod的IP地址。
Path:HTTP请求路径,默认值是/。
Port:HTTP请求端口号。
Scheme:协议类型,支持HTTP和HTTPS协议,默认是HTTP。
HttpHeaders:自定义HTTP请求头。
示例:访问 http://192.168.2.150:80/users
lifecycle: postStart: httpGet: path: /users port: 80 host: 192.168.2.150 scheme: HTTP # 或者HTTPS
Kubernetes源码(1.21.5,已在源码中移除dockershim模块):
pkg/kubelet/kuberuntime/kuberuntime_container.go:
开始容器方法主要包括拉取镜像、创建容器、start容器、运行容器postStart钩子函数。
// startContainer starts a container and returns a message indicates why it is failed on error. // It starts the container through the following steps: // * pull the image // * create the container // * start the container // * run the post start lifecycle hooks (if applicable) func (m *kubeGenericRuntimeManager) startContainer(podSandboxID string, podSandboxConfig *runtimeapi.PodSandboxConfig, spec *startSpec, pod *v1.Pod, podStatus *kubecontainer.PodStatus, pullSecrets []v1.Secret, podIP string, podIPs []string) (string, error) { container := spec.container // Step 1: pull the image. imageRef, msg, err := m.imagePuller.EnsureImageExists(pod, container, pullSecrets, podSandboxConfig) if err != nil { s, _ := grpcstatus.FromError(err) m.recordContainerEvent(pod, container, "", v1.EventTypeWarning, events.FailedToCreateContainer, "Error: %v", s.Message()) return msg, err } // Step 2: create the container. // For a new container, the RestartCount should be 0 restartCount := 0 containerStatus := podStatus.FindContainerStatusByName(container.Name) if containerStatus != nil { restartCount = containerStatus.RestartCount + 1 } target, err := spec.getTargetID(podStatus) if err != nil { s, _ := grpcstatus.FromError(err) m.recordContainerEvent(pod, container, "", v1.EventTypeWarning, events.FailedToCreateContainer, "Error: %v", s.Message()) return s.Message(), ErrCreateContainerConfig } containerConfig, cleanupAction, err := m.generateContainerConfig(container, pod, restartCount, podIP, imageRef, podIPs, target) if cleanupAction != nil { defer cleanupAction() } if err != nil { s, _ := grpcstatus.FromError(err) m.recordContainerEvent(pod, container, "", v1.EventTypeWarning, events.FailedToCreateContainer, "Error: %v", s.Message()) return s.Message(), ErrCreateContainerConfig } err = m.internalLifecycle.PreCreateContainer(pod, container, containerConfig) if err != nil { s, _ := grpcstatus.FromError(err) m.recordContainerEvent(pod, container, "", v1.EventTypeWarning, events.FailedToCreateContainer, "Internal PreCreateContainer hook failed: %v", s.Message()) return s.Message(), ErrPreCreateHook } containerID, err := m.runtimeService.CreateContainer(podSandboxID, containerConfig, podSandboxConfig) if err != nil { s, _ := grpcstatus.FromError(err) m.recordContainerEvent(pod, container, containerID, v1.EventTypeWarning, events.FailedToCreateContainer, "Error: %v", s.Message()) return s.Message(), ErrCreateContainer } err = m.internalLifecycle.PreStartContainer(pod, container, containerID) if err != nil { s, _ := grpcstatus.FromError(err) m.recordContainerEvent(pod, container, containerID, v1.EventTypeWarning, events.FailedToStartContainer, "Internal PreStartContainer hook failed: %v", s.Message()) return s.Message(), ErrPreStartHook } m.recordContainerEvent(pod, container, containerID, v1.EventTypeNormal, events.CreatedContainer, fmt.Sprintf("Created container %s", container.Name)) // Step 3: start the container. err = m.runtimeService.StartContainer(containerID) if err != nil { s, _ := grpcstatus.FromError(err) m.recordContainerEvent(pod, container, containerID, v1.EventTypeWarning, events.FailedToStartContainer, "Error: %v", s.Message()) return s.Message(), kubecontainer.ErrRunContainer } m.recordContainerEvent(pod, container, containerID, v1.EventTypeNormal, events.StartedContainer, fmt.Sprintf("Started container %s", container.Name)) // Symlink container logs to the legacy container log location for cluster logging // support. // TODO(random-liu): Remove this after cluster logging supports CRI container log path. containerMeta := containerConfig.GetMetadata() sandboxMeta := podSandboxConfig.GetMetadata() legacySymlink := legacyLogSymlink(containerID, containerMeta.Name, sandboxMeta.Name, sandboxMeta.Namespace) containerLog := filepath.Join(podSandboxConfig.LogDirectory, containerConfig.LogPath) // only create legacy symlink if containerLog path exists (or the error is not IsNotExist). // Because if containerLog path does not exist, only dangling legacySymlink is created. // This dangling legacySymlink is later removed by container gc, so it does not make sense // to create it in the first place. it happens when journald logging driver is used with docker. if _, err := m.osInterface.Stat(containerLog); !os.IsNotExist(err) { if err := m.osInterface.Symlink(containerLog, legacySymlink); err != nil { klog.ErrorS(err, "Failed to create legacy symbolic link", "path", legacySymlink, "containerID", containerID, "containerLogPath", containerLog) } } // Step 4: execute the post start hook. if container.Lifecycle != nil && container.Lifecycle.PostStart != nil { kubeContainerID := kubecontainer.ContainerID{ Type: m.runtimeName, ID: containerID, } msg, handlerErr := m.runner.Run(kubeContainerID, pod, container, container.Lifecycle.PostStart) if handlerErr != nil { m.recordContainerEvent(pod, container, kubeContainerID.ID, v1.EventTypeWarning, events.FailedPostStartHook, msg) if err := m.killContainer(pod, kubeContainerID, container.Name, "FailedPostStartHook", reasonFailedPostStartHook, nil); err != nil { klog.ErrorS(fmt.Errorf("%s: %v", ErrPostStartHook, handlerErr), "Failed to kill container", "pod", klog.KObj(pod), "podUID", pod.UID, "containerName", container.Name, "containerID", kubeContainerID.String()) } return msg, fmt.Errorf("%s: %v", ErrPostStartHook, handlerErr) } } return "", nil }
(1)关注下创建容器,kubelet调用docker csi,相当于执行 docker create 命令:
pkg/kubelet/cri/remote/remote_runtime.go:
// CreateContainer creates a new container in the specified PodSandbox. func (r *remoteRuntimeService) CreateContainer(podSandBoxID string, config *runtimeapi.ContainerConfig, sandboxConfig *runtimeapi.PodSandboxConfig) (string, error) { klog.V(10).InfoS("[RemoteRuntimeService] CreateContainer", "podSandboxID", podSandBoxID, "timeout", r.timeout) ctx, cancel := getContextWithTimeout(r.timeout) defer cancel() resp, err := r.runtimeClient.CreateContainer(ctx, &runtimeapi.CreateContainerRequest{ PodSandboxId: podSandBoxID, Config: config, SandboxConfig: sandboxConfig, }) if err != nil { klog.ErrorS(err, "CreateContainer in sandbox from runtime service failed", "podSandboxID", podSandBoxID) return "", err } klog.V(10).InfoS("[RemoteRuntimeService] CreateContainer", "podSandboxID", podSandBoxID, "containerID", resp.ContainerId) if resp.ContainerId == "" { errorMessage := fmt.Sprintf("ContainerId is not set for container %q", config.GetMetadata()) err := errors.New(errorMessage) klog.ErrorS(err, "CreateContainer failed") return "", err } return resp.ContainerId, nil }
(2)start容器,kubelet调用docker csi,相当于执行 docker start 命令:
pkg/kubelet/cri/remote/remote_runtime.go:
// StartContainer starts the container. func (r *remoteRuntimeService) StartContainer(containerID string) error { klog.V(10).InfoS("[RemoteRuntimeService] StartContainer", "containerID", containerID, "timeout", r.timeout) ctx, cancel := getContextWithTimeout(r.timeout) defer cancel() _, err := r.runtimeClient.StartContainer(ctx, &runtimeapi.StartContainerRequest{ ContainerId: containerID, }) if err != nil { klog.ErrorS(err, "StartContainer from runtime service failed", "containerID", containerID) return err } klog.V(10).InfoS("[RemoteRuntimeService] StartContainer Response", "containerID", containerID) return nil }
(3)运行容器postStart钩子函数(kubelet):
pkg/kubelet/lifecycle/handlers.go:
func (hr *handlerRunner) Run(containerID kubecontainer.ContainerID, pod *v1.Pod, container *v1.Container, handler *v1.Handler) (string, error) { switch { case handler.Exec != nil: var msg string // TODO(tallclair): Pass a proper timeout value. output, err := hr.commandRunner.RunInContainer(containerID, handler.Exec.Command, 0) if err != nil { msg = fmt.Sprintf("Exec lifecycle hook (%v) for Container %q in Pod %q failed - error: %v, message: %q", handler.Exec.Command, container.Name, format.Pod(pod), err, string(output)) klog.V(1).ErrorS(err, "Exec lifecycle hook for Container in Pod failed", "execCommand", handler.Exec.Command, "containerName", container.Name, "pod", klog.KObj(pod), "message", string(output)) } return msg, err case handler.HTTPGet != nil: msg, err := hr.runHTTPHandler(pod, container, handler) if err != nil { msg = fmt.Sprintf("HTTP lifecycle hook (%s) for Container %q in Pod %q failed - error: %v, message: %q", handler.HTTPGet.Path, container.Name, format.Pod(pod), err, msg) klog.V(1).ErrorS(err, "HTTP lifecycle hook for Container in Pod failed", "path", handler.HTTPGet.Path, "containerName", container.Name, "pod", klog.KObj(pod)) } return msg, err default: err := fmt.Errorf("invalid handler: %v", handler) msg := fmt.Sprintf("Cannot run handler: %v", err) klog.ErrorS(err, "Cannot run handler") return msg, err } }
cri-dockerd源码:
(1)创建容器
core/container_create.go:
// CreateContainer creates a new container in the given PodSandbox // Docker cannot store the log to an arbitrary location (yet), so we create an // symlink at LogPath, linking to the actual path of the log. func (ds *dockerService) CreateContainer( _ context.Context, r *v1.CreateContainerRequest, ) (*v1.CreateContainerResponse, error) { podSandboxID := r.PodSandboxId config := r.GetConfig() sandboxConfig := r.GetSandboxConfig() if config == nil { return nil, fmt.Errorf("container config is nil") } if sandboxConfig == nil { return nil, fmt.Errorf("sandbox config is nil for container %q", config.Metadata.Name) } labels := makeLabels(config.GetLabels(), config.GetAnnotations()) // Apply a the container type label. labels[containerTypeLabelKey] = containerTypeLabelContainer // Write the container log path in the labels. labels[containerLogPathLabelKey] = filepath.Join(sandboxConfig.LogDirectory, config.LogPath) // Write the sandbox ID in the labels. labels[sandboxIDLabelKey] = podSandboxID apiVersion, err := ds.getDockerAPIVersion() if err != nil { return nil, fmt.Errorf("unable to get the docker API version: %v", err) } image := "" if iSpec := config.GetImage(); iSpec != nil { image = iSpec.Image } containerName := makeContainerName(sandboxConfig, config) mounts := config.GetMounts() terminationMessagePath, _ := config.Annotations["io.kubernetes.container.terminationMessagePath"] sandboxInfo, err := ds.client.InspectContainer(r.GetPodSandboxId()) if err != nil { return nil, fmt.Errorf("unable to get container's sandbox ID: %v", err) } createConfig := dockerbackend.ContainerCreateConfig{ Name: containerName, Config: &container.Config{ Entrypoint: strslice.StrSlice(config.Command), Cmd: strslice.StrSlice(config.Args), Env: libdocker.GenerateEnvList(config.GetEnvs()), Image: image, WorkingDir: config.WorkingDir, Labels: labels, // Interactive containers: OpenStdin: config.Stdin, StdinOnce: config.StdinOnce, Tty: config.Tty, // Disable Docker's health check until we officially support it // (https://github.com/kubernetes/kubernetes/issues/25829). Healthcheck: &container.HealthConfig{ Test: []string{"NONE"}, }, }, HostConfig: &container.HostConfig{ Mounts: libdocker.GenerateMountBindings(mounts, terminationMessagePath), RestartPolicy: container.RestartPolicy{ Name: "no", }, Runtime: sandboxInfo.HostConfig.Runtime, }, } // Only request relabeling if the pod provides an SELinux context. If the pod // does not provide an SELinux context relabeling will label the volume with // the container's randomly allocated MCS label. This would restrict access // to the volume to the container which mounts it first. if selinuxOpts := config.GetLinux().GetSecurityContext().GetSelinuxOptions(); selinuxOpts != nil { mountLabel, err := selinuxMountLabel(selinuxOpts) if err != nil { return nil, fmt.Errorf("unable to generate SELinux mount label: %v", err) } if mountLabel != "" { // Equates to "Z" in the old bind API const shared = false for _, m := range mounts { if m.SelinuxRelabel { if err := label.Relabel(m.HostPath, mountLabel, shared); err != nil { return nil, fmt.Errorf("unable to relabel %q with %q: %v", m.HostPath, mountLabel, err) } } } } } hc := createConfig.HostConfig err = ds.updateCreateConfig( &createConfig, config, sandboxConfig, podSandboxID, securityOptSeparator, apiVersion, ) if err != nil { return nil, fmt.Errorf("failed to update container create config: %v", err) } // Set devices for container. devices := make([]container.DeviceMapping, len(config.Devices)) for i, device := range config.Devices { devices[i] = container.DeviceMapping{ PathOnHost: device.HostPath, PathInContainer: device.ContainerPath, CgroupPermissions: device.Permissions, } } hc.Resources.Devices = devices securityOpts, err := ds.getSecurityOpts( config.GetLinux().GetSecurityContext().GetSeccomp(), securityOptSeparator, ) if err != nil { return nil, fmt.Errorf( "failed to generate security options for container %q: %v", config.Metadata.Name, err, ) } hc.SecurityOpt = append(hc.SecurityOpt, securityOpts...) cleanupInfo, err := ds.applyPlatformSpecificDockerConfig(r, &createConfig) if err != nil { return nil, err } createResp, createErr := ds.client.CreateContainer(createConfig) if createErr != nil { createResp, createErr = recoverFromCreationConflictIfNeeded( ds.client, createConfig, createErr, ) } if createResp != nil { containerID := createResp.ID if cleanupInfo != nil { // we don't perform the clean up just yet at that could destroy information // needed for the container to start (e.g. Windows credentials stored in // registry keys); instead, we'll clean up when the container gets removed ds.setContainerCleanupInfo(containerID, cleanupInfo) } return &v1.CreateContainerResponse{ContainerId: containerID}, nil } // the creation failed, let's clean up right away - we ignore any errors though, // this is best effort ds.performPlatformSpecificContainerCleanupAndLogErrors(containerName, cleanupInfo) return nil, createErr }
调用CreateContainer方法(libdocker/kube_docker_client.go),然后作为 docker 客户端调用 docker 服务端 ContainerCreate 方法。
func (d *kubeDockerClient) CreateContainer( opts dockerbackend.ContainerCreateConfig, ) (*dockercontainer.CreateResponse, error) { ctx, cancel := context.WithTimeout(context.Background(), d.timeout) defer cancel() // we provide an explicit default shm size as to not depend on docker daemon. if opts.HostConfig != nil && opts.HostConfig.ShmSize <= 0 { opts.HostConfig.ShmSize = defaultShmSize } createResp, err := d.client.ContainerCreate( ctx, opts.Config, opts.HostConfig, opts.NetworkingConfig, nil, opts.Name, ) if ctxErr := contextError(ctx); ctxErr != nil { return nil, ctxErr } if err != nil { return nil, err } return &createResp, nil }
vendor/github.com/docker/docker/client/container_create.go:
// ContainerCreate creates a new container based on the given configuration. // It can be associated with a name, but it's not mandatory. func (cli *Client) ContainerCreate(ctx context.Context, config *container.Config, hostConfig *container.HostConfig, networkingConfig *network.NetworkingConfig, platform *ocispec.Platform, containerName string) (container.CreateResponse, error) { var response container.CreateResponse // Make sure we negotiated (if the client is configured to do so), // as code below contains API-version specific handling of options. // // Normally, version-negotiation (if enabled) would not happen until // the API request is made. if err := cli.checkVersion(ctx); err != nil { return response, err } if err := cli.NewVersionError(ctx, "1.25", "stop timeout"); config != nil && config.StopTimeout != nil && err != nil { return response, err } if err := cli.NewVersionError(ctx, "1.41", "specify container image platform"); platform != nil && err != nil { return response, err } if err := cli.NewVersionError(ctx, "1.44", "specify health-check start interval"); config != nil && config.Healthcheck != nil && config.Healthcheck.StartInterval != 0 && err != nil { return response, err } if err := cli.NewVersionError(ctx, "1.44", "specify mac-address per network"); hasEndpointSpecificMacAddress(networkingConfig) && err != nil { return response, err } if hostConfig != nil { if versions.LessThan(cli.ClientVersion(), "1.25") { // When using API 1.24 and under, the client is responsible for removing the container hostConfig.AutoRemove = false } if versions.GreaterThanOrEqualTo(cli.ClientVersion(), "1.42") || versions.LessThan(cli.ClientVersion(), "1.40") { // KernelMemory was added in API 1.40, and deprecated in API 1.42 hostConfig.KernelMemory = 0 } if platform != nil && platform.OS == "linux" && versions.LessThan(cli.ClientVersion(), "1.42") { // When using API under 1.42, the Linux daemon doesn't respect the ConsoleSize hostConfig.ConsoleSize = [2]uint{0, 0} } } // Since API 1.44, the container-wide MacAddress is deprecated and will trigger a WARNING if it's specified. if versions.GreaterThanOrEqualTo(cli.ClientVersion(), "1.44") { config.MacAddress = "" //nolint:staticcheck // ignore SA1019: field is deprecated, but still used on API < v1.44. } query := url.Values{} if p := formatPlatform(platform); p != "" { query.Set("platform", p) } if containerName != "" { query.Set("name", containerName) } body := configWrapper{ Config: config, HostConfig: hostConfig, NetworkingConfig: networkingConfig, } serverResp, err := cli.post(ctx, "/containers/create", query, body, nil) defer ensureReaderClosed(serverResp) if err != nil { return response, err } err = json.NewDecoder(serverResp.body).Decode(&response) return response, err }
(2)start容器
core/container_start.go
// StartContainer starts the container. func (ds *dockerService) StartContainer( _ context.Context, r *v1.StartContainerRequest, ) (*v1.StartContainerResponse, error) { err := ds.client.StartContainer(r.ContainerId) // Create container log symlink for all containers (including failed ones). if linkError := ds.createContainerLogSymlink(r.ContainerId); linkError != nil { // Do not stop the container if we failed to create symlink because: // 1. This is not a critical failure. // 2. We don't have enough information to properly stop container here. // Kubelet will surface this error to user via an event. return nil, linkError } if err != nil { err = transformStartContainerError(err) return nil, fmt.Errorf("failed to start container %q: %v", r.ContainerId, err) } return &v1.StartContainerResponse{}, nil }
libdocker/kube_docker_client.go
func (d *kubeDockerClient) StartContainer(id string) error { ctx, cancel := context.WithTimeout(context.Background(), d.timeout) defer cancel() err := d.client.ContainerStart(ctx, id, dockercontainer.StartOptions{}) if ctxErr := contextError(ctx); ctxErr != nil { return ctxErr } return err }
github.com/docker/docker/client/container_start.go
// ContainerStart sends a request to the docker daemon to start a container. func (cli *Client) ContainerStart(ctx context.Context, containerID string, options container.StartOptions) error { query := url.Values{} if len(options.CheckpointID) != 0 { query.Set("checkpoint", options.CheckpointID) } if len(options.CheckpointDir) != 0 { query.Set("checkpoint-dir", options.CheckpointDir) } resp, err := cli.post(ctx, "/containers/"+containerID+"/start", query, nil, nil) ensureReaderClosed(resp) return err }
moby源码(docker改名为moby):
(1)创建容器
api/server/router/container/container.go:
router.NewPostRoute("/containers/create", r.postContainersCreate),
api/server/router/container/container_routes.go:
func (s *containerRouter) postContainersCreate(ctx context.Context, w http.ResponseWriter, r *http.Request, vars map[string]string) error { if err := httputils.ParseForm(r); err != nil { return err } if err := httputils.CheckForJSON(r); err != nil { return err } name := r.Form.Get("name") config, hostConfig, networkingConfig, err := s.decoder.DecodeConfig(r.Body) if err != nil { return err } version := httputils.VersionFromContext(ctx) adjustCPUShares := versions.LessThan(version, "1.19") // When using API 1.24 and under, the client is responsible for removing the container if hostConfig != nil && versions.LessThan(version, "1.25") { hostConfig.AutoRemove = false } if hostConfig != nil && versions.LessThan(version, "1.40") { // Ignore BindOptions.NonRecursive because it was added in API 1.40. for _, m := range hostConfig.Mounts { if bo := m.BindOptions; bo != nil { bo.NonRecursive = false } } // Ignore KernelMemoryTCP because it was added in API 1.40. hostConfig.KernelMemoryTCP = 0 // Older clients (API < 1.40) expects the default to be shareable, make them happy if hostConfig.IpcMode.IsEmpty() { hostConfig.IpcMode = container.IPCModeShareable } } if hostConfig != nil && versions.LessThan(version, "1.41") && !s.cgroup2 { // Older clients expect the default to be "host" on cgroup v1 hosts if hostConfig.CgroupnsMode.IsEmpty() { hostConfig.CgroupnsMode = container.CgroupnsModeHost } } if hostConfig != nil && versions.LessThan(version, "1.42") { for _, m := range hostConfig.Mounts { // Ignore BindOptions.CreateMountpoint because it was added in API 1.42. if bo := m.BindOptions; bo != nil { bo.CreateMountpoint = false } // These combinations are invalid, but weren't validated in API < 1.42. // We reset them here, so that validation doesn't produce an error. if o := m.VolumeOptions; o != nil && m.Type != mount.TypeVolume { m.VolumeOptions = nil } if o := m.TmpfsOptions; o != nil && m.Type != mount.TypeTmpfs { m.TmpfsOptions = nil } if bo := m.BindOptions; bo != nil { // Ignore BindOptions.CreateMountpoint because it was added in API 1.42. bo.CreateMountpoint = false } } } if hostConfig != nil && versions.GreaterThanOrEqualTo(version, "1.42") { // Ignore KernelMemory removed in API 1.42. hostConfig.KernelMemory = 0 for _, m := range hostConfig.Mounts { if o := m.VolumeOptions; o != nil && m.Type != mount.TypeVolume { return errdefs.InvalidParameter(fmt.Errorf("VolumeOptions must not be specified on mount type %q", m.Type)) } if o := m.BindOptions; o != nil && m.Type != mount.TypeBind { return errdefs.InvalidParameter(fmt.Errorf("BindOptions must not be specified on mount type %q", m.Type)) } if o := m.TmpfsOptions; o != nil && m.Type != mount.TypeTmpfs { return errdefs.InvalidParameter(fmt.Errorf("TmpfsOptions must not be specified on mount type %q", m.Type)) } } } if hostConfig != nil && runtime.GOOS == "linux" && versions.LessThan(version, "1.42") { // ConsoleSize is not respected by Linux daemon before API 1.42 hostConfig.ConsoleSize = [2]uint{0, 0} } var platform *specs.Platform if versions.GreaterThanOrEqualTo(version, "1.41") { if v := r.Form.Get("platform"); v != "" { p, err := platforms.Parse(v) if err != nil { return errdefs.InvalidParameter(err) } platform = &p } } if hostConfig != nil && hostConfig.PidsLimit != nil && *hostConfig.PidsLimit <= 0 { // Don't set a limit if either no limit was specified, or "unlimited" was // explicitly set. // Both `0` and `-1` are accepted as "unlimited", and historically any // negative value was accepted, so treat those as "unlimited" as well. hostConfig.PidsLimit = nil } ccr, err := s.backend.ContainerCreate(types.ContainerCreateConfig{ Name: name, Config: config, HostConfig: hostConfig, NetworkingConfig: networkingConfig, AdjustCPUShares: adjustCPUShares, Platform: platform, }) if err != nil { return err } return httputils.WriteJSON(w, http.StatusCreated, ccr) }
(2)start容器
api/server/router/container/container.go:
router.NewPostRoute("/containers/{name:.*}/start", r.postContainersStart),
daemon/start.go:
// containerStart prepares the container to run by setting up everything the // container needs, such as storage and networking, as well as links // between containers. The container is left waiting for a signal to // begin running. func (daemon *Daemon) containerStart(container *container.Container, checkpoint string, checkpointDir string, resetRestartManager bool) (err error) { start := time.Now() container.Lock() defer container.Unlock() if resetRestartManager && container.Running { // skip this check if already in restarting step and resetRestartManager==false return nil } if container.RemovalInProgress || container.Dead { return errdefs.Conflict(errors.New("container is marked for removal and cannot be started")) } if checkpointDir != "" { // TODO(mlaventure): how would we support that? return errdefs.Forbidden(errors.New("custom checkpointdir is not supported")) } // if we encounter an error during start we need to ensure that any other // setup has been cleaned up properly defer func() { if err != nil { container.SetError(err) // if no one else has set it, make sure we don't leave it at zero if container.ExitCode() == 0 { container.SetExitCode(128) } if err := container.CheckpointTo(daemon.containersReplica); err != nil { logrus.Errorf("%s: failed saving state on start failure: %v", container.ID, err) } container.Reset(false) daemon.Cleanup(container) // if containers AutoRemove flag is set, remove it after clean up if container.HostConfig.AutoRemove { container.Unlock() if err := daemon.ContainerRm(container.ID, &types.ContainerRmConfig{ForceRemove: true, RemoveVolume: true}); err != nil { logrus.Errorf("can't remove container %s: %v", container.ID, err) } container.Lock() } } }() if err := daemon.conditionalMountOnStart(container); err != nil { return err } if err := daemon.initializeNetworking(container); err != nil { return err } spec, err := daemon.createSpec(container) if err != nil { return errdefs.System(err) } if resetRestartManager { container.ResetRestartManager(true) container.HasBeenManuallyStopped = false } if err := daemon.saveAppArmorConfig(container); err != nil { return err } if checkpoint != "" { checkpointDir, err = getCheckpointDir(checkpointDir, checkpoint, container.Name, container.ID, container.CheckpointDir(), false) if err != nil { return err } } shim, createOptions, err := daemon.getLibcontainerdCreateOptions(container) if err != nil { return err } ctx := context.TODO() err = daemon.containerd.Create(ctx, container.ID, spec, shim, createOptions) if err != nil { if errdefs.IsConflict(err) { logrus.WithError(err).WithField("container", container.ID).Error("Container not cleaned up from containerd from previous run") // best effort to clean up old container object daemon.containerd.DeleteTask(ctx, container.ID) if err := daemon.containerd.Delete(ctx, container.ID); err != nil && !errdefs.IsNotFound(err) { logrus.WithError(err).WithField("container", container.ID).Error("Error cleaning up stale containerd container object") } err = daemon.containerd.Create(ctx, container.ID, spec, shim, createOptions) } if err != nil { return translateContainerdStartErr(container.Path, container.SetExitCode, err) } } // TODO(mlaventure): we need to specify checkpoint options here pid, err := daemon.containerd.Start(context.Background(), container.ID, checkpointDir, container.StreamConfig.Stdin() != nil || container.Config.Tty, container.InitializeStdio) if err != nil { if err := daemon.containerd.Delete(context.Background(), container.ID); err != nil { logrus.WithError(err).WithField("container", container.ID). Error("failed to delete failed start container") } return translateContainerdStartErr(container.Path, container.SetExitCode, err) } container.HasBeenManuallyRestarted = false container.SetRunning(pid, true) container.HasBeenStartedBefore = true daemon.setStateCounter(container) daemon.initHealthMonitor(container) if err := container.CheckpointTo(daemon.containersReplica); err != nil { logrus.WithError(err).WithField("container", container.ID). Errorf("failed to store container") } daemon.LogContainerEvent(container, "start") containerActions.WithValues("start").UpdateSince(start) return nil }
源码分析见《详解Kubernetes Pod优雅退出》这篇博文,本文不再赘余。
在第三章节讲述开始容器方法时,我们已经很清晰知道,开始容器方法先运行容器,再运行运行容器 postStart 钩子函数。
需要注意的事,docker start 命令在启动容器时,并不会等待 ENTRYPOINT 命令执行完毕后才返回。它只会等待容器的主进程启动并确认其正常运行,然后立即返回。换句话说,docker start 命令返回时,ENTRYPOINT 命令已经开始执行,但不一定已经执行完毕。
所以PostStart的执行相对于容器主进程的执行是异步的,它会在容器start后立刻触发,并不能保证PostStart钩子在容器ENTRYPOINT之前运行。
apiVersion: v1 kind: Pod metadata: name: test-post-start spec: containers: - name: test-post-start-container image: busybox command: ["/bin/sh", "-c", "sleep 5 && echo $(date) 'written by entrypoint' >> log.log && sleep 600"] lifecycle: postStart: exec: command: ["/bin/sh", "-c", "sleep 10 && echo $(date) 'written by post start' >> log.log"]
创建上面的pod,通过进入pod,查看log.log打印日志,证明:
如果 PostStart 会阻挡 ENTRYPOINT 的启动,则日志文件内容应该是:
(时间点 T)written by post start (时间点 T + 约 10 秒)written by entrypoint
否则内容应该是:
(时间点 T)written by entrypoint (时间点 T + 约 5 秒)written by post start ```log
实验结果:
/ # cat log.log Thu Jun 4 06:14:50 UTC 2020 written by entrypoint Thu Jun 4 06:14:55 UTC 2020 written by post start
修改YAML文件:
apiVersion: v1 kind: Pod metadata: name: test-post-start spec: containers: - name: test-post-start-container image: busybox command: ["/bin/sh", "-c", "sleep 15 && echo $(date) 'written by entrypoint' >> log.log && sleep 600"] lifecycle: postStart: exec: command: ["/bin/sh", "-c", "sleep 10 && echo $(date) 'written by post start' >> log.log"]
如果 PostStart 不是异步执行,则日志文件内容应该是:
(时间点 T)written by entrypoint (时间点 T + 约 5 秒)written by post start ```log 否则内容应该是: ```log (时间点 T)written by post start (时间点 T + 约 5 秒)written by entrypoint
实验结果:
[root@master k8s]# kubectl exec -it test-post-start sh / # cat log.log Thu Jun 4 06:17:54 UTC 2020 written by post start Thu Jun 4 06:17:59 UTC 2020 written by entrypoint / #
容器生命周期钩子(PostStart和PreStop)提供在容器启动后和停止前执行自定义操作的能力,适用于数据库连接、文件下载、优雅终止等场景。postStart平时用的场景不是很多,重点关注preStop。