之前的文章k8s朋友圈中介绍promethues，promethues里面指标数据就是来源于各种exporter。

这里我们从零开始编写一个promethues的exporter。初始化我们第一个exporter 项目

#go mod init my_first_exporter 
#go get github.com/prometheus/client_golang 

首先指标定义

// Metrics
	up = prometheus.NewDesc(
		prometheus.BuildFQName(namespace, "", "up"),
		"Was the last Mirth query successful.",
		nil, nil,
	)
	messagesReceived = prometheus.NewDesc(
		prometheus.BuildFQName(namespace, "", "messages_received_total"),
		"How many messages have been received (per channel).",
		[]string{"channel"}, nil,
	)
	messagesFiltered = prometheus.NewDesc(
		prometheus.BuildFQName(namespace, "", "messages_filtered_total"),
		"How many messages have been filtered (per channel).",
		[]string{"channel"}, nil,
	)
	messagesQueued = prometheus.NewDesc(
		prometheus.BuildFQName(namespace, "", "messages_queued"),
		"How many messages are currently queued (per channel).",
		[]string{"channel"}, nil,
	)
	messagesSent = prometheus.NewDesc(
		prometheus.BuildFQName(namespace, "", "messages_sent_total"),
		"How many messages have been sent (per channel).",
		[]string{"channel"}, nil,
	)
	messagesErrored = prometheus.NewDesc(
		prometheus.BuildFQName(namespace, "", "messages_errored_total"),
		"How many messages have errored (per channel).",
		[]string{"channel"}, nil,
	)

然后启动我们的 http server

func main() {
	err := godotenv.Load()
	if err != nil {
		log.Println("Error loading .env file, assume env variables are set.")
	}

	flag.Parse()

	mirthEndpoint := os.Getenv("MIRTH_ENDPOINT")
	mirthUsername := os.Getenv("MIRTH_USERNAME")
	mirthPassword := os.Getenv("MIRTH_PASSWORD")

	exporter := NewExporter(mirthEndpoint, mirthUsername, mirthPassword)
	prometheus.MustRegister(exporter)

	http.Handle(*metricsPath, promhttp.Handler())
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte(`
             
             
             
Mirth Channel Exporter
             
Metrics
             
             `))
	})
	log.Fatal(http.ListenAndServe(*listenAddress, nil))
}

上面的代码注册了一个exporter，这个exporter负责收集指标。每一个exporter 都需要实现两个接口 Describe（指标描述） 和 Collect（数据采集），用于具体的指标采集。

type Exporter struct {
	mirthEndpoint, mirthUsername, mirthPassword string
}

func NewExporter(mirthEndpoint string, mirthUsername string, mirthPassword string) *Exporter {
	return &Exporter{
		mirthEndpoint: mirthEndpoint,
		mirthUsername: mirthUsername,
		mirthPassword: mirthPassword,
	}
}
// 指标描述
func (e *Exporter) Describe(ch chan<- *prometheus.Desc) {
	ch <- up
	ch <- messagesReceived
	ch <- messagesFiltered
	ch <- messagesQueued
	ch <- messagesSent
	ch <- messagesErrored
}

//数据采集
func (e *Exporter) Collect(ch chan<- prometheus.Metric) {
	channelIdNameMap, err := e.LoadChannelIdNameMap()
	if err != nil {
		ch <- prometheus.MustNewConstMetric(
			up, prometheus.GaugeValue, 0,
		)
		log.Println(err)
		return
	}
	ch <- prometheus.MustNewConstMetric(
		up, prometheus.GaugeValue, 1,
	)

//省略无用代码，这里主要是收集数据，并将采集的数据塞到channel 里面
  
		channelReceived, _ := strconv.ParseFloat(channelStatsList.Channels[i].Received, 64)
		ch <- prometheus.MustNewConstMetric(
			messagesReceived, prometheus.GaugeValue, channelReceived, channelName,
		)

		channelSent, _ := strconv.ParseFloat(channelStatsList.Channels[i].Sent, 64)
		ch <- prometheus.MustNewConstMetric(
			messagesSent, prometheus.GaugeValue, channelSent, channelName,
		)

		channelError, _ := strconv.ParseFloat(channelStatsList.Channels[i].Error, 64)
		ch <- prometheus.MustNewConstMetric(
			messagesErrored, prometheus.GaugeValue, channelError, channelName,
		)

		channelFiltered, _ := strconv.ParseFloat(channelStatsList.Channels[i].Filtered, 64)
		ch <- prometheus.MustNewConstMetric(
			messagesFiltered, prometheus.GaugeValue, channelFiltered, channelName,
		)

		channelQueued, _ := strconv.ParseFloat(channelStatsList.Channels[i].Queued, 64)
		ch <- prometheus.MustNewConstMetric(
			messagesQueued, prometheus.GaugeValue, channelQueued, channelName,
		)
  
}

可以通过容器启动，也可以通过Systemd 管理

[Unit]
Description=mirth channel exporter
After=network.target
[Service]
Type=simple
Restart=always
RestartSec=1
WorkingDirectory=/mirth/mirthconnect
EnvironmentFile=/etc/sysconfig/mirth_channel_exporter
ExecStart=/mirth/mirthconnect/mirth_channel_exporter

[Install]
WantedBy=multi-user.target

如果感兴趣还可以看看node exporter源代码，node exporter是负责采集主机的性能指标，在k8s里面经常被用于采集主机指标。