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.String()
		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.