kubernetes log combiner

klog.go

package main

import (
	"log"
	"os"
	"os/exec"
	"strings"
	"sync"
	"time"
)

var names = make(map[string]struct{})
var nameLock sync.RWMutex
var label string

func init() {
	label = os.Args[len(os.Args)-1]
}

func main() {
	for {
		pods := podNames()
		if len(pods) == 0 {
			log.Printf("No more pods. Quitting.\n")
			return
		}
		for _, pod := range pods {
			go watch(pod)
		}
		time.Sleep(time.Second * 30)
	}
}

func podNames() []string {
	cmd := exec.Command("kubectl", "get", "pods", "-o", "go-template={{ range .items }}{{ .metadata.name }} {{ end }}")
	out, err := cmd.CombinedOutput()
	if err != nil {
		log.Fatalf("Failed to get pod names: %s\n", err)
	}

	pods := make([]string, 0, 3)
	for _, pod := range strings.Fields(string(out)) {
		if strings.Contains(pod, label) {
			pods = append(pods, pod)
		}
	}
	return pods
}

func watch(name string) {
	if !claimName(name) {
		return
	}
	defer releaseName(name)
	log.Printf("Starting watch on %q\n", name)

	var cmd *exec.Cmd

	// get full history the first time only
	cmd = exec.Command("kubectl", "logs", "-f", name)
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stdout
	err := cmd.Run()
	if err != nil {
		log.Printf("Error reading log for pod %q: %s\n", name, err)
	}
}

func claimName(name string) bool {
	nameLock.Lock()
	defer nameLock.Unlock()
	if _, found := names[name]; found {
		return false
	}
	names[name] = struct{}{}
	return true
}

func releaseName(name string) {
	nameLock.Lock()
	delete(names, name)
	nameLock.Unlock()
}