gistfile1.txt

package main

import (
	"bytes"
	"encoding/json"
	"flag"
	"io"
	"log"
	"net"
	"os"
	"strings"
	"time"
)

type HealthCheck struct {
	LogType string    `json:"log_type"`
	Time    time.Time `json:"time"`
	Message string    `json:"message"`
}

// Send a health check ping to logstash via TCP
func SendCheck(h HealthCheck) error {
	b, err := json.Marshal(h)
	buf := bytes.NewBuffer(b)
	buf.WriteRune('\n')
	if err != nil {
		return err
	}
	conn, err := net.DialTimeout("tcp", "127.0.0.1:9999", time.Second*5)
	if err != nil {
		return err
	}
	_, err = conn.Write(buf.Bytes())
	if err != nil {
		return err
	}
	return nil
}

// Tail the stdout log file, and return the latest @timestamp
func CheckLog(logfile string, offset int64) (time.Time, error) {
	var t time.Time
	f, err := os.Open(logfile)
	if err != nil {
		return t, err
	}
	defer f.Close()
	stat, err := f.Stat()
	if err != nil {
		return t, err
	}
	s := stat.Size()
	if s < offset {
		offset = s
	}
	buf := make([]byte, offset)
	if _, err := f.ReadAt(buf, s-offset); err != nil && err != io.EOF {
		return t, err
	}
	for _, line := range strings.Split(string(buf[:]), "\n") {
		if strings.Contains(line, "@timestamp") {
			f := strings.Fields(line)
			if len(f) != 3 {
				continue
			}
			ts := strings.Replace(strings.Replace(f[2], `"`, "", -1), ",", "", -1)
			pt, err := time.Parse(time.RFC3339Nano, ts)
			if err != nil {
				return t, err
			}
			if t.Before(pt) {
				t = pt
			}
		}
	}
	return t, nil
}

var (
	flagSeek      = flag.Int64("s", 10000, "Number of lines to lookback in the log file.")
	flagThreshold = flag.Int64("t", 30, "Threshold for the age of the most recent timestamp in number of seconds.")
	flagWait      = flag.Int64("w", 20, "How many seconds to wait after submitting a request.")
)

func main() {
	flag.Parse()
	n := HealthCheck{LogType: "health-check", Message: "vrrp health check", Time: time.Now().UTC()}
	err := SendCheck(n)
	if err != nil {
		log.Fatal(err)
	}
	time.Sleep(time.Duration(*flagWait) * time.Second)
	t, err := CheckLog("/var/log/logstash/logstash.stdout", *flagSeek)
	if err != nil {
		log.Fatal(err)
	}
	if time.Now().UTC().Sub(t) > time.Second*time.Duration(*flagThreshold) {
		log.Fatal("No new timestamps, newest is ", t.UTC())
	}
}