🥇Kuidas töötab kubectl exec?

Märkus tõlke kohta.: artikli autor — Erkan Erol, insener SAP-ist — jagab oma õppimiskogemust käsu toimimise mehhanismidest. kubectl exec, mis on tuttav kõigile, kes töötavad Kubernetesega. Kogu algoritmi saatmiseks kasutab ta Kubernetes'e (ja seotud projektide) lähtekoodi loendeid, mis aitavad teemasse süveneda nii põhjalikult, kui vaja.

Ühel reedel tuli kolleeg minu juurde ja küsis, kuidas saaks käivitada käsku pod'is kasutades client-go. Ma ei osanud talle vastata ja ühtäkki mõistsin, et ma ei tea midagi selle töömehhanismi kohta. kubectl exec. Jah, mul olid teatud teadmised selle seadistusest, kuid ma ei olnud nende õigsuses 100% kindel ja seepärast otsustasin selle küsimusega tegelema hakata. Lugedes bloge, dokumentatsiooni ja lähtekoodi, sain palju uut teada ning soovin selles artiklis jagada oma avastusi ja mõistmist. Kui midagi on valesti, palun võtke minuga ühendust Twitteris.

Ettevalmistus

Klastri loomiseks MacBookil kloonisin ecomm-integration-ballerina/kubernetes-cluster. Seejärel muutsin kubeleti konfiguraatsioonis sõlmede IP-aadresse, kuna vaikeseaded ei lubanud täidesaatmist. kubectl exec. Peamise põhjuse kohta saab lugeda siin.

Iga masin = minu MacBook
Master-sõlme IP = 192.168.205.10
Töötaja-sõlme IP = 192.168.205.11
API-serveri port = 6443

Komponendid

kubectl exec protsess: kui käivitame «kubectl exec …», käivitub protsess. Seda saab teha igal masinal, millel on juurdepääs K8s API-serverile. Märkus tõlkijalt: Edasi konsolilehtede väljastustes kasutab autor kommentaari «iga masin», viidates sellele, et järgmisi käske saab käivitada igal sellisel masinal, millel on juurdepääs Kubernetes'ele.
API server: komponent master-sõlmes, mis annab juurdepääsu Kubernetes API-le. See on front-end control plane'i jaoks Kubernetes'e sees.
kubelet: agent, mis töötab igas sõlmes klastris. See tagab konteinerite tööd pod'is.
konteineri aeg (konteineri käitamise keskkond): tarkvara, mis vastutab konteinerite töö eest. Näited: Docker, CRI-O, containerd…
kernel: tööjaama OS-i südamik; vastutab protsesside haldamise eest.
target (siht-)konteiner : konteiner, mis on osa pod'ist ja töötab ühel töötaja-sõlmest.Mida ma avastasin

1. Klientide aktiivsus

Loome pod'i nimeses

default Seejärel käivitame exec käsu ja ootame 5000 sekundit, et jätkata jälgimist::

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

Seejärel käivitame käsu exec ja ootame 5000 sekundit edasiste jälgimiste jaoks:

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

Protsess kubectl ilmub (pid=8507 meie puhul):

// 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

Kui kontrollime protsessi võrgutegevust, leiame, et sel on ühendused api-serveriga (192.168.205.10:6443):

// 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

Vaadakem koodi. Kubectl loob POST-päringu subressursiga exec ja saadab REST-päringu:

              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)

(kubectl/pkg/cmd/exec/exec.go)

2. Tegevus master-i sõlmes

Saame ka jälgida päringut api-serveri poole:

handler.go:143] kube-apiserver: POST "/api/v1/namespaces/default/pods/exec-test-nginx-6558988d5-fgxgg/exec" rahuldati gorestful abil veebiteenusega /api/v1
upgradeaware.go:261] Ühendamine tagasipöörduva vahendiga (suunamiste intercept) https://192.168.205.11:10250/exec/default/exec-test-nginx-6558988d5-fgxgg/exec-test-nginx?command=sh&input=1&output=1&tty=1
Pealkirjad: 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]]

Pange tähele, et HTTP-päring sisaldab päringut protokolli muutmiseks. SPDY võimaldab multiplexida eraldi "siidid" stdin/stdout/stderr/spdy-error ühe TCP-ühenduse kaudu.

API-server saab päringu ja teisendab selle PodExecOptions:

// 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
}

(pkg/apis/core/types.go)

Nõutavate toimingute täitmiseks peab api-server teadma, millise podiga tal on vaja ühendust võtta:

// 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")
}

(pkg/registry/core/pod/strategy.go)

Loomulikult saadakse andmed endpoint'i kohta sõlme teabest:

        nodeName := types.NodeName(pod.Spec.NodeName)
        if len(nodeName) == 0 {
                // Kui pod ei ole määratud hostile, tagastage tühine asukoht
                return nil, nil, errors.NewBadRequest(fmt.Sprintf("pod %s ei ole määratud hostile", name))
        }
        nodeInfo, err := connInfo.GetConnectionInfo(ctx, nodeName)

(pkg/registry/core/pod/strategy.go)

Hura! Kubeleti jaoks on nüüd port (node.Status.DaemonEndpoints.KubeletEndpoint.Port), millele api-server saab ühenduda:

// 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
}

(pkg/kubelet/client/kubelet_client.go)

Dokumendist Master-Node Communication > Master to Cluster > apiserver to kubelet:
Need ühendused suunatakse läbi kubeleti HTTPS endpoint'i. Vaikimisi ei kontrolli apiserver kubeleti sertifikaati, mis muudab ühenduse keskvahendite rünnakute (MITM) suhtes haavatavaks ja ebaturvaliseks kasutamiseks usaldamatutes ja/või avalikes võrkudes.

Nüüd teab api-server endpoint'i ja seab ühenduse:

// 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
}

(pkg/registry/core/pod/rest/subresources.go)

Vaatame, mis meistrisõlmes toimub.

Esiteks saame teada töö sõlme IP-aadressi. Meie puhul on see 192.168.205.11:

// 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

Seejärel määrame kubelet'i pordi (meie puhul 10250):

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

Nüüd on aeg võrku kontrollida. Kas on ühendus töö sõlmega (192.168.205.11)? On! Kui "tappa" protsess, exec, kaob see, seega tean, et ühendus on api-server'iga loodud exec-käskluse sooritamise tulemusena.

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

Ühendus kubectl'i ja api-server'i vahel on endiselt avatud. Lisaks on veel üks ühendus, mis seob api-server'i ja kubelet'i.

3. Aktiviteet töö sõlmes

Nüüd ühendame töö sõlme ja vaatame, mis seal toimub.

Ennekõike näeme, et ühendus on ka loodud (teine rida); 192.168.205.10 on meistri sõlme IP aadress:

 // 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

Kuidas on meie käsuga sleep? Ура, она тоже присутствует!

 // 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
  …

Aga oota: kuidas kubelet seda tegi? Kubelet'is on deemon, mis avab juurdepääsu API-le pordi kaudu api-server'i päringuteks:

// 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
}

(pkg/kubelet/server/streaming/server.go)

Kubelet arvutab vastava lõpp-punkti exec-päringute jaoks:

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
}

(pkg/kubelet/server/streaming/server.go)

Ära eksige. See ei tagasta käsu tulemust, vaid suhtluse lõpp-punkti:

type ExecResponse struct {
        /// Täielikult kvalifitseeritud URL exec voogesituse serverile.
        Url                  string   `protobuf:"bytes,1,opt,name=url,proto3" json:"url,omitempty"`
        XXX_NoUnkeyedLiteral struct{} `json:"-"`
        XXX_sizecache        int32    `json:"-"`
}

(cri-api/pkg/apis/runtime/v1alpha2/api.pb.go)

Kubelet rakendab liidest RuntimeServiceClient, mis on osa Container Runtime Interface'ist (rohkema kohta oleme kirjutanud, näiteks, siin — toimetaja märkus):

Pikk loend cri-api'ist kubernetes/kubernetes

// 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 (e.g., 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 (i.e., 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)
}

(cri-api/pkg/apis/runtime/v1alpha2/api.pb.go)
See lihtsalt kasutab gRPC meetodi kutsumiseks läbi Container Runtime Interface:

type runtimeServiceClient struct {
        cc *grpc.ClientConn
}

(cri-api/pkg/apis/runtime/v1alpha2/api.pb.go)

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
}

(cri-api/pkg/apis/runtime/v1alpha2/api.pb.go)

Container Runtime vastutab RuntimeServiceServer:

Pikk loend cri-api'ist kubernetes/kubernetes

// 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 (e.g., 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 (i.e., 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)
}

(cri-api/pkg/apis/runtime/v1alpha2/api.pb.go)

Kui nii, peaksime nägema ühendust kubelet'i ja konteinerite täituriga, eks? Kontrollime seda.

Käivitage see käsk enne ja pärast exec-käsku ning vaadake erinevusi. Minu puhul on erinevus järgmine:

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

Hmm... Uus ühendus unix-sokettide kaudu kubelet'iga (pid=5714) ja millegagi tundmatuga. Mis see võiks olla? Õige, see on Docker (pid=1186)!

// 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))
...

Kuidas te mäletate, see on docker-demon (pid=1186), mis täidab meie käsku:

// 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. Tegevus konteineri täitmisruumis

Uurime CRI-O lähtekoodi, et mõista, mis toimub. Docker'is on loogika sarnane.

On server, mis vastutab rakenduse eest RuntimeServiceServer:

// 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
}

(cri-o/server/server.go)

// 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
}

(cri-o/erver/container_exec.go)

Lõpusüsteemis täidab konteineri keskkond käsku töönodes:

// 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
}

(cri-o/internal/oci/runtime_oci.go)

Lõpuks täidab kernel käsklusi:

Märkmed

API Server võib samuti algatada ühenduse kubelet'iga.
Järgmised ühendused salvestatakse kuni interaktiivse exec-seansi lõpuni:
- kubectl ja api-server'i vahel;
- api-server'i ja kubectl'i vahel;
- kubelet'i ja konteineri täitmisruumi vahel.
Kubectl või api-server ei saa midagi töönodes käivitada. Kubelet saab käivitada, kuid nende toimingute jaoks suhtleb ta ka konteineri täitmisruumiga.