How to get logs from kubernetes using Go?

Question

I'm looking for the solution of how to get logs from a pod in Kubernetes cluster using Go. 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Update: The solution provided in Kubernetes go client api for log of a particular pod is out of date.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

The answer by anon_coword got me interested, in getting logs in a bit more complicated case:

1. I want to preform the action multiple times, and check the logs multiple times.
2. I want to have many pods that will react the same way.

Here are a few examples: https://github.com/nwaizer/GetPodLogsEfficiently One example is:

package main

import (
    "GetPodLogsEfficiently/client"
    "GetPodLogsEfficiently/utils"
    "bufio"
    "context"
    "fmt"
    corev1 "k8s.io/api/core/v1"
    "time"
)

func GetPodLogs(cancelCtx context.Context, PodName string) {
    PodLogsConnection := client.Client.Pods(utils.Namespace).GetLogs(PodName, &corev1.PodLogOptions{
        Follow:    true,
        TailLines: &[]int64{int64(10)}[0],
    })
    LogStream, _ := PodLogsConnection.Stream(context.Background())
    defer LogStream.Close()

    reader := bufio.NewScanner(LogStream)
    var line string
    for {
        select {
        case <-cancelCtx.Done():
            break
        default:
            for reader.Scan() {
                line = reader.Text()
                fmt.Printf("Pod: %v line: %v\n", PodName, line)
            }
        }
    }
}
func main() {
    ctx := context.Background()
    cancelCtx, endGofunc := context.WithCancel(ctx)
    for _, pod := range utils.GetPods().Items {
        fmt.Println(pod.Name)
        go GetPodLogs(cancelCtx, pod.Name)
    }
    time.Sleep(10 * time.Second)
    endGofunc()
}