How to Execute Kubernetes Exec Commands Using the Go Client?

Kubernetes Exec Command Example Using Go Client

Problem:

Executing commands in a pod using the Kubernetes Go client can be challenging. Users may encounter errors without clear messages when attempting to stream the execution output.

Solution:

To correctly execute commands in a pod with the Kubernetes Go client, follow these steps:

1. Create a Kubernetes client configuration using the restclient.Config struct, specifying the server host and setting Insecure to true for testing purposes.
2. Initialize the client using the RESTClientFor function and specify the API group version and negotiated serializer.
3. Construct the request by creating a Post() request builder for the pods resource. Set the pod name, namespace, and subresource (exec) in the request builder.
4. Specify the PodExecOptions and use the ParameterCodec to encode the parameters.
5. Use the NewExecutor function to create an Executor for the given config, HTTP method, and URL.
6. Initialize the stream execution options and specify the stdin, stdout, and stderr streams as well as the TTY setting.
7. Call the Stream function to execute the command.

Note:

The code example provided in the question uses an incorrect version of the PodExecOptions struct. The correct version is from the v1 package (not the unversioned package).

Working Example:

The following code demonstrates a working example of executing commands in a pod using the Kubernetes Go client:

package k8s

import (
    "io"

    v1 "k8s.io/api/core/v1"
    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/kubernetes/scheme"
    restclient "k8s.io/client-go/rest"
    "k8s.io/client-go/tools/remotecommand"
)

// ExecCmd exec command on specific pod and wait the command's output.
func ExecCmdExample(client kubernetes.Interface, config *restclient.Config, podName string,
    command string, stdin io.Reader, stdout io.Writer, stderr io.Writer) error {
    cmd := []string{
        "sh",
        "-c",
        command,
    }
    req := client.CoreV1().RESTClient().Post().Resource("pods").Name(podName).
        Namespace("default").SubResource("exec")
    option := &v1.PodExecOptions{
        Command: cmd,
        Stdin:   true,
        Stdout:  true,
        Stderr:  true,
        TTY:     true,
    }
    if stdin == nil {
        option.Stdin = false
    }
    req.VersionedParams(
        option,
        scheme.ParameterCodec,
    )
    exec, err := remotecommand.NewSPDYExecutor(config, "POST", req.URL())
    if err != nil {
        return err
    }
    err = exec.Stream(remotecommand.StreamOptions{
        Stdin:  stdin,
        Stdout: stdout,
        Stderr: stderr,
    })
    if err != nil {
        return err
    }

    return nil
}

This code correctly uses the v1 version of PodExecOptions and sets the TTY parameter to true, enabling interactive command execution if desired.

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