Comment fonctionne kubectl exec?

La préparation

• Toute voiture = mon MacBook
• IP maître = 192.168.205.10
• IP hôte de travail = 192.168.205.11
• Port du serveur API = 6443

Composants

• Processus kubectl exec : lorsque nous exécutons «kubectl exec ...», le processus démarre. Vous pouvez le faire sur n'importe quelle machine ayant accès au serveur API K8s. Remarque trans.: Plus loin dans les listes de consoles, l'auteur utilise le commentaire "n'importe quelle machine", ce qui implique que les commandes suivantes peuvent être exécutées sur toutes ces machines avec accès à Kubernetes.
• serveur api : un composant sur le maître qui donne accès à l'API Kubernetes. Ceci est l'interface du plan de contrôle dans Kubernetes.
• kubelet : un agent qui s'exécute sur chaque nœud du cluster. Il fournit des conteneurs en pod'e.
• runtime conteneur ( runtime conteneur ): logiciel responsable du fonctionnement des conteneurs. Exemples: Docker, CRI-O, containerd ...
• noyau : noyau du système d'exploitation sur le nœud de travail; responsable de la gestion des processus.
• conteneur cible : conteneur qui fait partie d'un pod et fonctionne sur l'un des nœuds de travail.

Ce que j'ai découvert

1. Activité côté client

 // any machine $ kubectl run exec-test-nginx --image=nginx 

 // any machine $ kubectl exec -it exec-test-nginx-6558988d5-fgxgg -- sh # sleep 5000 

 // any machine $ ps -ef |grep kubectl 501 8507 8409 0 7:19PM ttys000 0:00.13 kubectl exec -it exec-test-nginx-6558988d5-fgxgg -- sh 

 // any machine $ netstat -atnv |grep 8507 tcp4 0 0 192.168.205.1.51673 192.168.205.10.6443 ESTABLISHED 131072 131768 8507 0 0x0102 0x00000020 tcp4 0 0 192.168.205.1.51672 192.168.205.10.6443 ESTABLISHED 131072 131768 8507 0 0x0102 0x00000028 

  req := restClient.Post(). Resource("pods"). Name(pod.Name). Namespace(pod.Namespace). SubResource("exec") req.VersionedParams(&corev1.PodExecOptions{ Container: containerName, Command: p.Command, Stdin: p.Stdin, Stdout: p.Out != nil, Stderr: p.ErrOut != nil, TTY: t.Raw, }, scheme.ParameterCodec) return p.Executor.Execute("POST", req.URL(), p.Config, p.In, p.Out, p.ErrOut, t.Raw, sizeQueue) 

2. Activité sur le côté du nœud maître

 handler.go:143] kube-apiserver: POST "/api/v1/namespaces/default/pods/exec-test-nginx-6558988d5-fgxgg/exec" satisfied by gorestful with webservice /api/v1 upgradeaware.go:261] Connecting to backend proxy (intercepting redirects) https://192.168.205.11:10250/exec/default/exec-test-nginx-6558988d5-fgxgg/exec-test-nginx?command=sh&input=1&output=1&tty=1 Headers: map[Connection:[Upgrade] Content-Length:[0] Upgrade:[SPDY/3.1] User-Agent:[kubectl/v1.12.10 (darwin/amd64) kubernetes/e3c1340] X-Forwarded-For:[192.168.205.1] X-Stream-Protocol-Version:[v4.channel.k8s.io v3.channel.k8s.io v2.channel.k8s.io channel.k8s.io]] 

 // PodExecOptions is the query options to a Pod's remote exec call type PodExecOptions struct { metav1.TypeMeta // Stdin if true indicates that stdin is to be redirected for the exec call Stdin bool // Stdout if true indicates that stdout is to be redirected for the exec call Stdout bool // Stderr if true indicates that stderr is to be redirected for the exec call Stderr bool // TTY if true indicates that a tty will be allocated for the exec call TTY bool // Container in which to execute the command. Container string // Command is the remote command to execute; argv array; not executed within a shell. Command []string } 

 // ExecLocation returns the exec URL for a pod container. If opts.Container is blank // and only one container is present in the pod, that container is used. func ExecLocation( getter ResourceGetter, connInfo client.ConnectionInfoGetter, ctx context.Context, name string, opts *api.PodExecOptions, ) (*url.URL, http.RoundTripper, error) { return streamLocation(getter, connInfo, ctx, name, opts, opts.Container, "exec") } 

  nodeName := types.NodeName(pod.Spec.NodeName) if len(nodeName) == 0 { // If pod has not been assigned a host, return an empty location return nil, nil, errors.NewBadRequest(fmt.Sprintf("pod %s does not have a host assigned", name)) } nodeInfo, err := connInfo.GetConnectionInfo(ctx, nodeName) 

 // GetConnectionInfo retrieves connection info from the status of a Node API object. func (k *NodeConnectionInfoGetter) GetConnectionInfo(ctx context.Context, nodeName types.NodeName) (*ConnectionInfo, error) { node, err := k.nodes.Get(ctx, string(nodeName), metav1.GetOptions{}) if err != nil { return nil, err } // Find a kubelet-reported address, using preferred address type host, err := nodeutil.GetPreferredNodeAddress(node, k.preferredAddressTypes) if err != nil { return nil, err } // Use the kubelet-reported port, if present port := int(node.Status.DaemonEndpoints.KubeletEndpoint.Port) if port <= 0 { port = k.defaultPort } return &ConnectionInfo{ Scheme: k.scheme, Hostname: host, Port: strconv.Itoa(port), Transport: k.transport, }, nil } 

De la documentation de Communication Master-Node> Master to Cluster> apiserver to kubelet :

Ces connexions sont fermées sur le point de terminaison HTTPS de kubelet. Par défaut, apiserver ne vérifie pas le certificat du kubelet, ce qui rend la connexion vulnérable aux «attaques intermédiaires» (MITM) et peu sûre pour travailler sur des réseaux non fiables et / ou publics.

 // Connect returns a handler for the pod exec proxy func (r *ExecREST) Connect(ctx context.Context, name string, opts runtime.Object, responder rest.Responder) (http.Handler, error) { execOpts, ok := opts.(*api.PodExecOptions) if !ok { return nil, fmt.Errorf("invalid options object: %#v", opts) } location, transport, err := pod.ExecLocation(r.Store, r.KubeletConn, ctx, name, execOpts) if err != nil { return nil, err } return newThrottledUpgradeAwareProxyHandler(location, transport, false, true, true, responder), nil } 

 // any machine $ kubectl get nodes k8s-node-1 -o wide NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME k8s-node-1 Ready <none> 9h v1.15.3 192.168.205.11 <none> Ubuntu 16.04.6 LTS 4.4.0-159-generic docker://17.3.3 

 // any machine $ kubectl get nodes k8s-node-1 -o jsonpath='{.status.daemonEndpoints.kubeletEndpoint}' map[Port:10250] 

 // master node $ netstat -atn |grep 192.168.205.11 tcp 0 0 192.168.205.10:37870 192.168.205.11:10250 ESTABLISHED … 

3. Activité sur le nœud de travail

  // worker node $ netstat -atn |grep 10250 tcp6 0 0 :::10250 :::* LISTEN tcp6 0 0 192.168.205.11:10250 192.168.205.10:37870 ESTABLISHED 

  // worker node $ ps -afx ... 31463 ? Sl 0:00 \_ docker-containerd-shim 7d974065bbb3107074ce31c51f5ef40aea8dcd535ae11a7b8f2dd180b8ed583a /var/run/docker/libcontainerd/7d974065bbb3107074ce31c51 31478 pts/0 Ss 0:00 \_ sh 31485 pts/0 S+ 0:00 \_ sleep 5000 … 

 // Server is the library interface to serve the stream requests. type Server interface { http.Handler // Get the serving URL for the requests. // Requests must not be nil. Responses may be nil iff an error is returned. GetExec(*runtimeapi.ExecRequest) (*runtimeapi.ExecResponse, error) GetAttach(req *runtimeapi.AttachRequest) (*runtimeapi.AttachResponse, error) GetPortForward(*runtimeapi.PortForwardRequest) (*runtimeapi.PortForwardResponse, error) // Start the server. // addr is the address to serve on (address:port) stayUp indicates whether the server should // listen until Stop() is called, or automatically stop after all expected connections are // closed. Calling Get{Exec,Attach,PortForward} increments the expected connection count. // Function does not return until the server is stopped. Start(stayUp bool) error // Stop the server, and terminate any open connections. Stop() error } 

 func (s *server) GetExec(req *runtimeapi.ExecRequest) (*runtimeapi.ExecResponse, error) { if err := validateExecRequest(req); err != nil { return nil, err } token, err := s.cache.Insert(req) if err != nil { return nil, err } return &runtimeapi.ExecResponse{ Url: s.buildURL("exec", token), }, nil } 

 type ExecResponse struct { // Fully qualified URL of the exec streaming server. Url string `protobuf:"bytes,1,opt,name=url,proto3" json:"url,omitempty"` XXX_NoUnkeyedLiteral struct{} `json:"-"` XXX_sizecache int32 `json:"-"` } 

 // For semantics around ctx use and closing/ending streaming RPCs, please refer to https://godoc.org/google.golang.org/grpc#ClientConn.NewStream. type RuntimeServiceClient interface { // Version returns the runtime name, runtime version, and runtime API version. Version(ctx context.Context, in *VersionRequest, opts ...grpc.CallOption) (*VersionResponse, error) // RunPodSandbox creates and starts a pod-level sandbox. Runtimes must ensure // the sandbox is in the ready state on success. RunPodSandbox(ctx context.Context, in *RunPodSandboxRequest, opts ...grpc.CallOption) (*RunPodSandboxResponse, error) // StopPodSandbox stops any running process that is part of the sandbox and // reclaims network resources (eg, IP addresses) allocated to the sandbox. // If there are any running containers in the sandbox, they must be forcibly // terminated. // This call is idempotent, and must not return an error if all relevant // resources have already been reclaimed. kubelet will call StopPodSandbox // at least once before calling RemovePodSandbox. It will also attempt to // reclaim resources eagerly, as soon as a sandbox is not needed. Hence, // multiple StopPodSandbox calls are expected. StopPodSandbox(ctx context.Context, in *StopPodSandboxRequest, opts ...grpc.CallOption) (*StopPodSandboxResponse, error) // RemovePodSandbox removes the sandbox. If there are any running containers // in the sandbox, they must be forcibly terminated and removed. // This call is idempotent, and must not return an error if the sandbox has // already been removed. RemovePodSandbox(ctx context.Context, in *RemovePodSandboxRequest, opts ...grpc.CallOption) (*RemovePodSandboxResponse, error) // PodSandboxStatus returns the status of the PodSandbox. If the PodSandbox is not // present, returns an error. PodSandboxStatus(ctx context.Context, in *PodSandboxStatusRequest, opts ...grpc.CallOption) (*PodSandboxStatusResponse, error) // ListPodSandbox returns a list of PodSandboxes. ListPodSandbox(ctx context.Context, in *ListPodSandboxRequest, opts ...grpc.CallOption) (*ListPodSandboxResponse, error) // CreateContainer creates a new container in specified PodSandbox CreateContainer(ctx context.Context, in *CreateContainerRequest, opts ...grpc.CallOption) (*CreateContainerResponse, error) // StartContainer starts the container. StartContainer(ctx context.Context, in *StartContainerRequest, opts ...grpc.CallOption) (*StartContainerResponse, error) // StopContainer stops a running container with a grace period (ie, timeout). // This call is idempotent, and must not return an error if the container has // already been stopped. // TODO: what must the runtime do after the grace period is reached? StopContainer(ctx context.Context, in *StopContainerRequest, opts ...grpc.CallOption) (*StopContainerResponse, error) // RemoveContainer removes the container. If the container is running, the // container must be forcibly removed. // This call is idempotent, and must not return an error if the container has // already been removed. RemoveContainer(ctx context.Context, in *RemoveContainerRequest, opts ...grpc.CallOption) (*RemoveContainerResponse, error) // ListContainers lists all containers by filters. ListContainers(ctx context.Context, in *ListContainersRequest, opts ...grpc.CallOption) (*ListContainersResponse, error) // ContainerStatus returns status of the container. If the container is not // present, returns an error. ContainerStatus(ctx context.Context, in *ContainerStatusRequest, opts ...grpc.CallOption) (*ContainerStatusResponse, error) // UpdateContainerResources updates ContainerConfig of the container. UpdateContainerResources(ctx context.Context, in *UpdateContainerResourcesRequest, opts ...grpc.CallOption) (*UpdateContainerResourcesResponse, error) // ReopenContainerLog asks runtime to reopen the stdout/stderr log file // for the container. This is often called after the log file has been // rotated. If the container is not running, container runtime can choose // to either create a new log file and return nil, or return an error. // Once it returns error, new container log file MUST NOT be created. ReopenContainerLog(ctx context.Context, in *ReopenContainerLogRequest, opts ...grpc.CallOption) (*ReopenContainerLogResponse, error) // ExecSync runs a command in a container synchronously. ExecSync(ctx context.Context, in *ExecSyncRequest, opts ...grpc.CallOption) (*ExecSyncResponse, error) // Exec prepares a streaming endpoint to execute a command in the container. Exec(ctx context.Context, in *ExecRequest, opts ...grpc.CallOption) (*ExecResponse, error) // Attach prepares a streaming endpoint to attach to a running container. Attach(ctx context.Context, in *AttachRequest, opts ...grpc.CallOption) (*AttachResponse, error) // PortForward prepares a streaming endpoint to forward ports from a PodSandbox. PortForward(ctx context.Context, in *PortForwardRequest, opts ...grpc.CallOption) (*PortForwardResponse, error) // ContainerStats returns stats of the container. If the container does not // exist, the call returns an error. ContainerStats(ctx context.Context, in *ContainerStatsRequest, opts ...grpc.CallOption) (*ContainerStatsResponse, error) // ListContainerStats returns stats of all running containers. ListContainerStats(ctx context.Context, in *ListContainerStatsRequest, opts ...grpc.CallOption) (*ListContainerStatsResponse, error) // UpdateRuntimeConfig updates the runtime configuration based on the given request. UpdateRuntimeConfig(ctx context.Context, in *UpdateRuntimeConfigRequest, opts ...grpc.CallOption) (*UpdateRuntimeConfigResponse, error) // Status returns the status of the runtime. Status(ctx context.Context, in *StatusRequest, opts ...grpc.CallOption) (*StatusResponse, error) } 

 type runtimeServiceClient struct { cc *grpc.ClientConn } 

 func (c *runtimeServiceClient) Exec(ctx context.Context, in *ExecRequest, opts ...grpc.CallOption) (*ExecResponse, error) { out := new(ExecResponse) err := c.cc.Invoke(ctx, "/runtime.v1alpha2.RuntimeService/Exec", in, out, opts...) if err != nil { return nil, err } return out, nil } 

 // RuntimeServiceServer is the server API for RuntimeService service. type RuntimeServiceServer interface { // Version returns the runtime name, runtime version, and runtime API version. Version(context.Context, *VersionRequest) (*VersionResponse, error) // RunPodSandbox creates and starts a pod-level sandbox. Runtimes must ensure // the sandbox is in the ready state on success. RunPodSandbox(context.Context, *RunPodSandboxRequest) (*RunPodSandboxResponse, error) // StopPodSandbox stops any running process that is part of the sandbox and // reclaims network resources (eg, IP addresses) allocated to the sandbox. // If there are any running containers in the sandbox, they must be forcibly // terminated. // This call is idempotent, and must not return an error if all relevant // resources have already been reclaimed. kubelet will call StopPodSandbox // at least once before calling RemovePodSandbox. It will also attempt to // reclaim resources eagerly, as soon as a sandbox is not needed. Hence, // multiple StopPodSandbox calls are expected. StopPodSandbox(context.Context, *StopPodSandboxRequest) (*StopPodSandboxResponse, error) // RemovePodSandbox removes the sandbox. If there are any running containers // in the sandbox, they must be forcibly terminated and removed. // This call is idempotent, and must not return an error if the sandbox has // already been removed. RemovePodSandbox(context.Context, *RemovePodSandboxRequest) (*RemovePodSandboxResponse, error) // PodSandboxStatus returns the status of the PodSandbox. If the PodSandbox is not // present, returns an error. PodSandboxStatus(context.Context, *PodSandboxStatusRequest) (*PodSandboxStatusResponse, error) // ListPodSandbox returns a list of PodSandboxes. ListPodSandbox(context.Context, *ListPodSandboxRequest) (*ListPodSandboxResponse, error) // CreateContainer creates a new container in specified PodSandbox CreateContainer(context.Context, *CreateContainerRequest) (*CreateContainerResponse, error) // StartContainer starts the container. StartContainer(context.Context, *StartContainerRequest) (*StartContainerResponse, error) // StopContainer stops a running container with a grace period (ie, timeout). // This call is idempotent, and must not return an error if the container has // already been stopped. // TODO: what must the runtime do after the grace period is reached? StopContainer(context.Context, *StopContainerRequest) (*StopContainerResponse, error) // RemoveContainer removes the container. If the container is running, the // container must be forcibly removed. // This call is idempotent, and must not return an error if the container has // already been removed. RemoveContainer(context.Context, *RemoveContainerRequest) (*RemoveContainerResponse, error) // ListContainers lists all containers by filters. ListContainers(context.Context, *ListContainersRequest) (*ListContainersResponse, error) // ContainerStatus returns status of the container. If the container is not // present, returns an error. ContainerStatus(context.Context, *ContainerStatusRequest) (*ContainerStatusResponse, error) // UpdateContainerResources updates ContainerConfig of the container. UpdateContainerResources(context.Context, *UpdateContainerResourcesRequest) (*UpdateContainerResourcesResponse, error) // ReopenContainerLog asks runtime to reopen the stdout/stderr log file // for the container. This is often called after the log file has been // rotated. If the container is not running, container runtime can choose // to either create a new log file and return nil, or return an error. // Once it returns error, new container log file MUST NOT be created. ReopenContainerLog(context.Context, *ReopenContainerLogRequest) (*ReopenContainerLogResponse, error) // ExecSync runs a command in a container synchronously. ExecSync(context.Context, *ExecSyncRequest) (*ExecSyncResponse, error) // Exec prepares a streaming endpoint to execute a command in the container. Exec(context.Context, *ExecRequest) (*ExecResponse, error) // Attach prepares a streaming endpoint to attach to a running container. Attach(context.Context, *AttachRequest) (*AttachResponse, error) // PortForward prepares a streaming endpoint to forward ports from a PodSandbox. PortForward(context.Context, *PortForwardRequest) (*PortForwardResponse, error) // ContainerStats returns stats of the container. If the container does not // exist, the call returns an error. ContainerStats(context.Context, *ContainerStatsRequest) (*ContainerStatsResponse, error) // ListContainerStats returns stats of all running containers. ListContainerStats(context.Context, *ListContainerStatsRequest) (*ListContainerStatsResponse, error) // UpdateRuntimeConfig updates the runtime configuration based on the given request. UpdateRuntimeConfig(context.Context, *UpdateRuntimeConfigRequest) (*UpdateRuntimeConfigResponse, error) // Status returns the status of the runtime. Status(context.Context, *StatusRequest) (*StatusResponse, error) } 

 // worker node $ ss -a -p |grep kubelet ... u_str ESTAB 0 0 * 157937 * 157387 users:(("kubelet",pid=5714,fd=33)) ... 

 // worker node $ ss -a -p |grep 157387 ... u_str ESTAB 0 0 * 157937 * 157387 users:(("kubelet",pid=5714,fd=33)) u_str ESTAB 0 0 /var/run/docker.sock 157387 * 157937 users:(("dockerd",pid=1186,fd=14)) ... 

 // worker node $ ps -afx ... 1186 ? Ssl 0:55 /usr/bin/dockerd -H fd:// 17784 ? Sl 0:00 \_ docker-containerd-shim 53a0a08547b2f95986402d7f3b3e78702516244df049ba6c5aa012e81264aa3c /var/run/docker/libcontainerd/53a0a08547b2f95986402d7f3 17801 pts/2 Ss 0:00 \_ sh 17827 pts/2 S+ 0:00 \_ sleep 5000 ... 

4. Activité dans le runtime du conteneur

 // Server implements the RuntimeService and ImageService type Server struct { config libconfig.Config seccompProfile *seccomp.Seccomp stream StreamService netPlugin ocicni.CNIPlugin hostportManager hostport.HostPortManager appArmorProfile string hostIP string bindAddress string *lib.ContainerServer monitorsChan chan struct{} defaultIDMappings *idtools.IDMappings systemContext *types.SystemContext // Never nil updateLock sync.RWMutex seccompEnabled bool appArmorEnabled bool } 

 // Exec prepares a streaming endpoint to execute a command in the container. func (s *Server) Exec(ctx context.Context, req *pb.ExecRequest) (resp *pb.ExecResponse, err error) { const operation = "exec" defer func() { recordOperation(operation, time.Now()) recordError(operation, err) }() resp, err = s.getExec(req) if err != nil { return nil, fmt.Errorf("unable to prepare exec endpoint: %v", err) } return resp, nil } 

 // ExecContainer prepares a streaming endpoint to execute a command in the container. func (r *runtimeOCI) ExecContainer(c *Container, cmd []string, stdin io.Reader, stdout, stderr io.WriteCloser, tty bool, resize <-chan remotecommand.TerminalSize) error { processFile, err := prepareProcessExec(c, cmd, tty) if err != nil { return err } defer os.RemoveAll(processFile.Name()) args := []string{rootFlag, r.root, "exec"} args = append(args, "--process", processFile.Name(), c.ID()) execCmd := exec.Command(r.path, args...) if v, found := os.LookupEnv("XDG_RUNTIME_DIR"); found { execCmd.Env = append(execCmd.Env, fmt.Sprintf("XDG_RUNTIME_DIR=%s", v)) } var cmdErr, copyError error if tty { cmdErr = ttyCmd(execCmd, stdin, stdout, resize) } else { if stdin != nil { // Use an os.Pipe here as it returns true *os.File objects. // This way, if you run 'kubectl exec <pod> -i bash' (no tty) and type 'exit', // the call below to execCmd.Run() can unblock because its Stdin is the read half // of the pipe. r, w, err := os.Pipe() if err != nil { return err } go func() { _, copyError = pools.Copy(w, stdin) }() execCmd.Stdin = r } if stdout != nil { execCmd.Stdout = stdout } if stderr != nil { execCmd.Stderr = stderr } cmdErr = execCmd.Run() } if copyError != nil { return copyError } if exitErr, ok := cmdErr.(*exec.ExitError); ok { return &utilexec.ExitErrorWrapper{ExitError: exitErr} } return cmdErr } 

Rappels

• API Server peut également initier une connexion à kubelet.
• Les connexions suivantes sont maintenues jusqu'à la fin de la session d'exécution interactive:
  • entre kubectl et api-server;
  • entre api-server et kubectl;
  • entre le kubelet et l'exécution du conteneur.
• Kubectl ou api-server ne peuvent rien exécuter sur les nœuds de production. Kubelet peut démarrer, mais pour ces actions, il interagit également avec le runtime du conteneur.

Les ressources

• La discussion " Comment" kubectl exec "fonctionne " dans kubernetes-dev;
• Article " Jouer avec le kubeadm dans les machines vagabondes, partie 2 ";
• La discussion " Comment trouver une autre fin de connexion socket Unix? "On Server Fault.

PS du traducteur

• "Que se passe-t-il dans Kubernetes lorsque l'exécution de kubectl démarre?" Partie 1 et partie 2 ;
• « Alors, qu'est-ce qu'un pod dans Kubernetes? ";
• " Comment fonctionne le planificateur Kubernetes?" ";
• " Comment la haute disponibilité chez Kubernetes est assurée ."