Metrik dan Pemantauan

Mengekspos metrik aplikasi memungkinkan Anda memantau tingkat permintaan, latensi, tingkat error, dan penggunaan sumber daya di produksi. Prometheus adalah sistem pemantauan paling umum yang digunakan dengan aplikasi Go.

Using gin-contrib/openmetrics

The gin-contrib/openmetrics middleware provides a ready-to-use Prometheus metrics endpoint:

go get github.com/gin-contrib/openmetrics

package main

import (
  "github.com/gin-contrib/openmetrics"
  "github.com/gin-gonic/gin"
)

func main() {
  r := gin.Default()

  // Expose /metrics endpoint for Prometheus scraping
  r.Use(openmetrics.NewOpenMetrics("myapp", openmetrics.WithExpose()))

  r.GET("/ping", func(c *gin.Context) {
    c.JSON(200, gin.H{"message": "pong"})
  })

  r.Run(":8080")
}

Custom Prometheus metrics

For more control, use the prometheus/client_golang library directly:

package main

import (
  "strconv"
  "time"

  "github.com/gin-gonic/gin"
  "github.com/prometheus/client_golang/prometheus"
  "github.com/prometheus/client_golang/prometheus/promhttp"
)

var (
  httpRequestsTotal = prometheus.NewCounterVec(
    prometheus.CounterOpts{
      Name: "http_requests_total",
      Help: "Total number of HTTP requests",
    },
    []string{"method", "path", "status"},
  )

  httpRequestDuration = prometheus.NewHistogramVec(
    prometheus.HistogramOpts{
      Name:    "http_request_duration_seconds",
      Help:    "HTTP request duration in seconds",
      Buckets: prometheus.DefBuckets,
    },
    []string{"method", "path"},
  )
)

func init() {
  prometheus.MustRegister(httpRequestsTotal)
  prometheus.MustRegister(httpRequestDuration)
}

func MetricsMiddleware() gin.HandlerFunc {
  return func(c *gin.Context) {
    start := time.Now()

    c.Next()

    duration := time.Since(start).Seconds()
    status := strconv.Itoa(c.Writer.Status())

    httpRequestsTotal.WithLabelValues(c.Request.Method, c.FullPath(), status).Inc()
    httpRequestDuration.WithLabelValues(c.Request.Method, c.FullPath()).Observe(duration)
  }
}

func main() {
  r := gin.Default()
  r.Use(MetricsMiddleware())

  // Expose metrics endpoint (separate from application routes)
  r.GET("/metrics", gin.WrapH(promhttp.Handler()))

  r.GET("/ping", func(c *gin.Context) {
    c.JSON(200, gin.H{"message": "pong"})
  })

  r.Run(":8080")
}

Key metrics to monitor

For a production Gin application, track these metrics:

Metric	Type	Purpose
`http_requests_total`	Counter	Total request count by method, path, status
`http_request_duration_seconds`	Histogram	Request latency distribution
`http_requests_in_flight`	Gauge	Currently processing requests
`http_response_size_bytes`	Histogram	Response body sizes

Serving metrics on a separate port

In production, serve metrics on a separate port to keep them internal:

package main

import (
  "net/http"

  "github.com/gin-gonic/gin"
  "github.com/prometheus/client_golang/prometheus/promhttp"
)

func main() {
  // Application server
  app := gin.Default()
  app.GET("/ping", func(c *gin.Context) {
    c.JSON(200, gin.H{"message": "pong"})
  })

  // Metrics server on a separate port
  go func() {
    metrics := http.NewServeMux()
    metrics.Handle("/metrics", promhttp.Handler())
    http.ListenAndServe(":9090", metrics)
  }()

  app.Run(":8080")
}

This way, you can expose port 8080 publicly while keeping port 9090 internal to your infrastructure.

Prometheus scrape configuration

Add your application to the Prometheus configuration:

scrape_configs:
  - job_name: "gin-app"
    scrape_interval: 15s
    static_configs:
      - targets: ["localhost:9090"]

Testing

# Generate some traffic
curl http://localhost:8080/ping

# Check metrics
curl http://localhost:9090/metrics

You should see output like:

# HELP http_requests_total Total number of HTTP requests
# TYPE http_requests_total counter
http_requests_total{method="GET",path="/ping",status="200"} 1

# HELP http_request_duration_seconds HTTP request duration in seconds
# TYPE http_request_duration_seconds histogram
http_request_duration_seconds_bucket{method="GET",path="/ping",le="0.005"} 1
...