go-gin-prometheus

Gin Web Framework Prometheus metrics exporter

Installation

$ go get github.com/zsais/go-gin-prometheus

Usage

package main

import (
    "github.com/gin-gonic/gin"
    "github.com/zsais/go-gin-prometheus"
)

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

    p := ginprometheus.NewPrometheus("gin")
    p.Use(r)

    r.GET("/", func(c *gin.Context) {
        c.JSON(200, "Hello world!")
    })

    r.Run(":29090")
}

See the example.go file

Preserving a low cardinality for the request counter

The request counter (requests_total) has a url label which, although desirable, can become problematic in cases where your application uses templated routes expecting a great number of variations, as Prometheus explicitly recommends against metrics having high cardinality dimensions:

https://prometheus.io/docs/practices/naming/#labels

If you have for instance a /customer/:name templated route and you don't want to generate a time series for every possible customer name, you could supply this mapping function to the middleware:

package main

import (
    "github.com/gin-gonic/gin"
    "github.com/zsais/go-gin-prometheus"
)

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

    p := ginprometheus.NewPrometheus("gin")

    p.ReqCntURLLabelMappingFn = func(c *gin.Context) string {
        url := c.Request.URL.Path
        for _, p := range c.Params {
            if p.Key == "name" {
                url = strings.Replace(url, p.Value, ":name", 1)
                break
            }
        }
        return url
    }

    p.Use(r)

    r.GET("/", func(c *gin.Context) {
        c.JSON(200, "Hello world!")
    })

    r.Run(":29090")
}

which would map /customer/alice and /customer/bob to their template /customer/:name, and thus preserve a low cardinality for our metrics.