// BAD - unique per user/request
counter := promauto.NewCounterVec(
prometheus.CounterOpts{Name: "requests_total"},
[]string{"user_id", "path"}, // millions of series!
)
counter.WithLabelValues(userID, request.URL.Path).Inc()
// GOOD - bounded label values
counter := promauto.NewCounterVec(
prometheus.CounterOpts{Name: "requests_total"},
[]string{"method", "status_code"}, // <100 series
)
counter.WithLabelValues(r.Method, statusCode).Inc()
// BAD - using gauge for monotonic value
requestCount := promauto.NewGauge(prometheus.GaugeOpts{
Name: "http_requests",
})
requestCount.Inc() // should be Counter!
// GOOD
requestCount := promauto.NewCounter(prometheus.CounterOpts{
Name: "http_requests_total",
})
requestCount.Inc()
// BAD - new metric per request
func handler(w http.ResponseWriter, r *http.Request) {
counter := prometheus.NewCounter(...) // creates new each time!
prometheus.MustRegister(counter) // panics on duplicate!
}
// GOOD - register once
var requestCounter = promauto.NewCounter(prometheus.CounterOpts{
Name: "http_requests_total",
})
func handler(w http.ResponseWriter, r *http.Request) {
requestCounter.Inc()
}
// BAD
duration := promauto.NewHistogram(prometheus.HistogramOpts{
Name: "request_duration", // no unit!
})
// GOOD
duration := promauto.NewHistogram(prometheus.HistogramOpts{
Name: "request_duration_seconds", // unit in name
})
var (
httpRequests = promauto.NewCounterVec(
prometheus.CounterOpts{
Namespace: "myapp",
Subsystem: "http",
Name: "requests_total",
Help: "Total HTTP requests processed",
},
[]string{"method", "status"},
)
httpDuration = promauto.NewHistogramVec(
prometheus.HistogramOpts{
Namespace: "myapp",
Subsystem: "http",
Name: "request_duration_seconds",
Help: "HTTP request latencies",
Buckets: []float64{.005, .01, .025, .05, .1, .25, .5, 1, 2.5, 5, 10},
},
[]string{"method"},
)
)
func metricsMiddleware(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
timer := prometheus.NewTimer(httpDuration.WithLabelValues(r.Method))
defer timer.ObserveDuration()
wrapped := &responseWriter{ResponseWriter: w, status: 200}
next.ServeHTTP(wrapped, r)
httpRequests.WithLabelValues(r.Method, strconv.Itoa(wrapped.status)).Inc()
})
}
import "github.com/prometheus/client_golang/prometheus/promhttp"
func main() {
http.Handle("/metrics", promhttp.Handler())
http.ListenAndServe(":9090", nil)
}