Go: What are Go and Prometheus metrics?

1import (
2    "net/http"
3    "github.com/prometheus/client_golang/prometheus"
4    "github.com/prometheus/client_golang/prometheus/promhttp"
5)
6
7// Metric definitions
8var (
9    httpRequestsTotal = prometheus.NewCounterVec(
10        prometheus.CounterOpts{
11            Name: "http_requests_total",
12            Help: "Total HTTP requests",
13        },
14        []string{"method", "path", "status"},
15    )
16
17    httpRequestDuration = prometheus.NewHistogramVec(
18        prometheus.HistogramOpts{
19            Name:    "http_request_duration_seconds",
20            Help:    "HTTP request duration",
21            Buckets: []float64{0.01, 0.05, 0.1, 0.5, 1, 5},
22        },
23        []string{"method", "path"},
24    )
25
26    dbQueryDuration = prometheus.NewHistogram(
27        prometheus.HistogramOpts{
28            Name:    "db_query_duration_seconds",
29            Help:    "Database query duration",
30            Buckets: prometheus.DefBuckets,
31        },
32    )
33)
34
35func init() {
36    prometheus.MustRegister(httpRequestsTotal)
37    prometheus.MustRegister(httpRequestDuration)
38    prometheus.MustRegister(dbQueryDuration)
39}
40
41// Middleware
42func MetricsMiddleware(next http.Handler) http.Handler {
43    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
44        start := time.Now()
45
46        next.ServeHTTP(w, r)
47
48        duration := time.Since(start).Seconds()
49        status := w.Header().Get("X-Status")
50
51        httpRequestsTotal.WithLabelValues(r.Method, r.URL.Path, status).Inc()
52        httpRequestDuration.WithLabelValues(r.Method, r.URL.Path).Observe(duration)
53    })
54}
55
56// Endpoint for Prometheus
57func main() {
58    http.Handle("/metrics", promhttp.Handler())
59    http.Handle("/api/", MetricsMiddleware(handler))
60    log.Fatal(http.ListenAndServe(":8080", nil))
61}