go-http-metrics

To get started, you need to create a middleware factory using middleware.New with a middleware.Config, and then wrap your HTTP handlers using a framework-specific provider (e.g., middlewarestd.Handler for the standard library).

This example demonstrates using Prometheus as the recorder with the standard Go net/http library:

package main

import (
    "log"
    "net/http"

    "github.com/prometheus/client_golang/prometheus/promhttp"
    metrics "github.com/slok/go-http-metrics/metrics/prometheus"
    "github.com/slok/go-http-metrics/middleware"
    middlewarestd "github.com/slok/go-http-metrics/middleware/std"
)

func main() {
    // Create our middleware.
    mdlw := middleware.New(middleware.Config{
        Recorder: metrics.NewRecorder(metrics.Config{}),
    })

    // Our handler.
    h := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        w.WriteHeader(http.StatusOK)
        w.Write([]byte("hello world!"))
    })
    h = middlewarestd.Handler("", mdlw, h)

    // Serve metrics.
    log.Printf("serving metrics at: %s", ":9090")
    go http.ListenAndServe(":9090", promhttp.Handler())

    // Serve our handler.
    log.Printf("listening at: %s", ":8080")
    if err := http.ListenAndServe(":8080", h); err != nil {
        log.Panicf("error while serving: %s", err)
    }
}

The middleware.Config object controls how the middleware behaves. Key options include:

• Recorder: The implementation of the metrics backend (e.g., Prometheus or OpenCensus). Defaults to a dummy recorder.
• Service: An optional string to set a specific service name on all metrics. Useful for distinguishing between different servers (e.g., API vs Metrics server) using the same recorder.
• GroupedStatus: If enabled, status codes are grouped into the dxx form (e.g., 4xx instead of 401, 404). This reduces cardinality but loses detail. Disabled by default.
• DisableMeasureSize: If true, stops measuring response sizes.
• DisableMeasureInflight: If true, stops measuring concurrent (inflight) requests.
• IgnoredPaths: A list of paths that will not be measured for duration or response size, though they will still be counted in RequestsInflight.

Note on Handler IDs: When wrapping a handler, you provide a handlerID.

• If you pass an empty string "", the handler label is derived from the URL path. This can cause high cardinality if paths contain dynamic parameters (e.g., /p/123/dashboard).
• If you pass a predefined pattern like "/p/:userID/dashboard/:page", cardinality remains low because dynamic segments are collapsed into the pattern.