Golang Prometheus Exporter - 按需拉取指标

Question

根据prometheus 文档中的定义，在编写导出器时，它声明以下内容：

仅当 Prometheus 抓取指标时才应从应用程序中提取指标，导出器不应根据自己的计时器执行抓取。

以下代码在技术上工作正常，并使用我的自定义指标发布适当的页面。所以它按原样解决了我的业务需求。

然而，它效率低下并且运行无限循环来不断更新值。这与上面提到的仅在 Prometheus 抓取时生成指标值的文档中的做法不符。

package main

import (
    "log"
    "net/http"
    "time"

    "github.com/prometheus/client_golang/prometheus"
    "github.com/prometheus/client_golang/prometheus/promhttp"
)

func main() {
    var metricSystemTime = prometheus.NewGauge(prometheus.GaugeOpts{
        Name: "custom_system_time", Help: "Timestamp in unix epoch format"})

    prometheus.MustRegister(metricSystemTime)

    go startServer()

    for {
        metricSystemTime.Set(float64(time.Now().Unix()))
        time.Sleep(1 * time.Second)
    }
}

func startServer() {
    http.Handle("/metrics", promhttp.Handler())
    log.Fatal(http.ListenAndServe(":19100", nil))
}

为了仅在 prometheus 抓取导出器端点时提取指标，这意味着我需要以某种方式侦听对象上的 GET 请求http.ListenAndServe()？我怎样才能做到这一点？

在我的阅读中，我发现http.HandlerFunc()相反，http.Handler()它似乎走在正确的道路上，但我无法让它工作promhttp.Handler()，而且我在其中迷失了方向。

Answer 1

经过大量搜索后弄清楚了。希望这对将来的人有帮助。

这是一个工作导出器，满足仅在普罗米修斯刮擦发生时收集指标的要求

• 没有无限循环，没有内部计时器。
• 每次 Prometheus 抓取导出器时都会发布新指标，如原始问题的文档中所定义。

package main

import (
    "log"
    "net/http"
    "time"

    "github.com/prometheus/client_golang/prometheus"
    "github.com/prometheus/client_golang/prometheus/promhttp"
)

type Collector struct {
    // Add one of the below lines for each collector you define in the newCollector() function
    systemTime    *prometheus.Desc
}

// Declare your exporter metrics here. Referred to as "collectors"
func newCollector() *Collector {
    return &Collector{
        systemTime: prometheus.NewDesc("my_system_time",
            "System timestamp in unix epoch format",
            nil, nil,
        ),
        // Add more collectors (aka metric definitions) here 
    }
}

func (collector *Collector) Describe(ch chan<- *prometheus.Desc) {
    // Add one of these lines for each of your collectors declared above
    ch <- collector.systemTime
}

// This fuction runs when Prometheus scrapes the exporter. It will set a new value for the metric(s)
// I have no idea how it works, but it does.
func (collector *Collector) Collect(ch chan<- prometheus.Metric) {

    var setSystemTime float64

    // Calculate the value of the metric
    setSystemTime = float64(time.Now().Unix())

    // Here is where you set the "new" value for the metric
    // This example is a Gauge, but it can be any Prom metric type
    ch <- prometheus.MustNewConstMetric(collector.systemTime, prometheus.GaugeValue, setSystemTime)
}

// Main function, spawns the collector and the web server
func main() {
    collector := newCollector()
    prometheus.MustRegister(collector)

    http.Handle("/metrics", promhttp.Handler())
    log.Fatal(http.ListenAndServe(":19100", nil))
}