How to get logs from kubernetes using golang?

Question

I'm looking for the solution of how to get logs from a pod in Kubernetes cluster using golang. I've looked at "https://github.com/kubernetes/client-go" and "https://godoc.org/sigs.k8s.io/controller-runtime/pkg/client", but couldn't understand how to use them for this purpose. I have no issues getting information of a pod or any other object in K8S except for logs.

For example, I'm using Get() from "https://godoc.org/sigs.k8s.io/controller-runtime/pkg/client#example-Client--Get" to get K8S job info:

found := &batchv1.Job{}
err = r.client.Get(context.TODO(), types.NamespacedName{Name: job.Name, Namespace: job.Namespace}, found)

Please share of how you get pod's logs nowadays. Any suggestions would be appreciated!

Update: The solution provided in Kubernetes go client api for log of a particular pod is out of date. It have some tips, but it is not up to date with current libraries.

Answer 1

@Emixam23

I believe you will find this snippet useful.

How to get the dynamic name of a pod?

import  metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"

    labelSelector := metav1.LabelSelector{MatchLabels: map[string]string{<LABEL_KEY>: <LABEL_VALUE>}}
    listOptions := metav1.ListOptions{
        LabelSelector: labels.Set(labelSelector.MatchLabels).String(),
    }
    pod, err := k8sClient.CoreV1().Pods(<NAMESPACE>).List(listOptions)
    podName := pod.Items[0].ObjectMeta.Name

Answer 2

Here is what we came up with eventually using client-go library:

func getPodLogs(pod corev1.Pod) string {
    podLogOpts := corev1.PodLogOptions{}
    config, err := rest.InClusterConfig()
    if err != nil {
        return "error in getting config"
    }
    // creates the clientset
    clientset, err := kubernetes.NewForConfig(config)
    if err != nil {
        return "error in getting access to K8S"
    }
    req := clientset.CoreV1().Pods(pod.Namespace).GetLogs(pod.Name, &podLogOpts)
    podLogs, err := req.Stream()
    if err != nil {
        return "error in opening stream"
    }
    defer podLogs.Close()

    buf := new(bytes.Buffer)
    _, err = io.Copy(buf, podLogs)
    if err != nil {
        return "error in copy information from podLogs to buf"
    }
    str := buf.String()

    return str
}

I hope it will help someone. Please share your thoughts or solutions of how you get logs from pods in Kubernetes.

Answer 3

The controller-runtime client library does not yet support subresources other than /status, so you would have to use client-go as shown in the other question.