promlog

---

forked klog hook to expose the number of log messages as Prometheus metrics:

log_messages_total{severity="ERROR"} 0
log_messages_total{severity="INFO"} 42
log_messages_total{severity="WARNING"} 0

Usage

Sample code:

package main

import (
	"net/http"
	"time"

	"github.com/prometheus/client_golang/prometheus/promhttp"
	"github.com/practo/klog/v2"
	"github.com/practo/promlog"
)

func main() {
	// Create the Prometheus hook:
	hook := promlog.MustNewPrometheusHook("", klog.InfoSeverityLevel)

	// Configure klog to use the Prometheus hook:
	klog.AddHook(hook)

	// Expose Prometheus metrics via HTTP, as you usually would:
	go http.ListenAndServe(":8080", promhttp.Handler())

	// Log with klog, as you usually would.
	// Every time the program generates a log message,
	// a Prometheus counter is incremented for the corresponding level.
	for {
		klog.Infof("foo")
		time.Sleep(1 * time.Second)
	}
}

Run the above program:

$ cd example && go run main.go
I0624 13:26:39.035027   51136 main.go:26] foo
I0624 13:26:40.035543   51136 main.go:26] foo
I0624 13:26:41.039174   51136 main.go:26] foo
I0624 13:26:42.039930   51136 main.go:26] foo
I0624 13:26:43.041310   51136 main.go:26] foo

Scrape the Prometheus metrics exposed by the hook:

$ curl -fsS localhost:8080 | grep log_messages
# HELP log_messages_total Total number of log messages.
# TYPE log_messages_total counter
log_messages_total{severity="ERROR"} 0
log_messages_total{severity="INFO"} 42
log_messages_total{severity="WARNING"} 0

Compile

$ go build

Test

$ go test
I0624 13:27:29.696765   51237 promlog_test.go:49] this is at info level!
W0624 13:27:29.697785   51237 promlog_test.go:55] this is at warning level!
E0624 13:27:29.698964   51237 promlog_test.go:61] this is at error level!
PASS
ok  	github.com/practo/promlog	0.237s