Exporter 是 Prometheus 监控的核心，如果你遇到一些应用不存在相应的 Exporter，那么我们可以自己去编写 Exporter。下面我们简单介绍如何使用 Golang 来快速编写一个 Exporter。
1. 安装 GO 和依赖包
按照 https://golang.org/doc/install 上的步骤进行安装配置 GO 环境，创建一个名为 my_first_exporter 的文件夹。
代码语言：javascript复制$ go mod init my_first_exporter
$ go get github.com/prometheus/client_golang
$ go get github.com/joho/godotenv
--> creates go.mod file
--> Installs dependency into the go.mod file
2. 创建入口点和导入依赖包
代码语言：javascript复制package main
import (
"github.com/joho/godotenv"
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promhttp"
)
3. 创建 main() 函数
代码语言：javascript复制func main()
4. 添加 prometheus metrics 端点，并在某个服务端口上监听
代码语言：javascript复制func main() {
http.Handle("/metrics", promhttp.Handler())
log.Fatal(http.ListenAndServe(":9101", nil))
}
5. 使用 curl 请求外部服务接口
比如我们这里监控的应用程序是 MirthConnect，所以我需要进行两个 API 接口调用：
- 获取 channel 统计数据
- 获取 channel id 和名称映射
curl -k --location --request GET 'https://apihost/api/channels/statistics'
--user admin:admin
curl -k --location --request GET 'https://apihost/api/channels/idsAndNames'
--user admin:admin
6. 将 curl 调用转换为 go http 调用，并解析结果
如果你是 Go 新手，这应该是最困难的一步。对于我这里的例子，端点返回的是 XML 格式的数据，所以我必须用 "encoding/xml" 包来反序列化 XML。转换成功后意味着我的 GO 程序可以执行和 curl 命令一样的 API 调用。
7. 声明 Prometheus metrics
在 Prometheus 中，每个 metric 指标都由以下几个部分组成：metric name/metric label values/metric help text/metric type/measurement ，例如：
Example:
# HELP promhttp_metric_handler_requests_total Total number of scrapes by HTTP status code.
# TYPE promhttp_metric_handler_requests_total counter
promhttp_metric_handler_requests_total{code=”200"} 1.829159e 06
promhttp_metric_handler_requests_total{code=”500"} 0
promhttp_metric_handler_requests_total{code=”503"} 0
对于应用 scrapers，我们将定义 Prometheus metrics 描述信息，其中包括 metric 名称、metric label 标签以及 metric 帮助信息。
代码语言：javascript复制messagesReceived = prometheus.NewDesc(
prometheus.BuildFQName(namespace, "", "messages_received_total"),
"How many messages have been received (per channel).",
[]string{"channel"}, nil,
)
8. 定义一个结构体实现 Prometheus 的 Collector 接口
Prometheus 的 client 库提供了实现自定义 Exportor 的接口，Collector 接口定义了两个方法 Describe 和 Collect，实现这两个方法就可以暴露自定义的数据：
- Describe(chan<- *Desc)
- Collect(chan<- Metric)
如下所示：
代码语言：javascript复制type Exporter struct {
mirthEndpoint, mirthUsername, mirthPassword string
}
func NewExporter(mirthEndpoint string, mirthUsername string, mirthPassword string) *Exporter {
return &Exporter{
mirthEndpoint: mirthEndpoint,
mirthUsername: mirthUsername,
mirthPassword: mirthPassword,
}
}
func (e *Exporter) Describe(ch chan<- *prometheus.Desc) {
}
func (e *Exporter) Collect(ch chan<- prometheus.Metric) {
}
9. 在 Describe 函数中，把第7步的 metric 描述信息发送给它
代码语言：javascript复制func (e *Exporter) Describe(ch chan<- *prometheus.Desc) {
ch <- up
ch <- messagesReceived
ch <- messagesFiltered
ch <- messagesQueued
ch <- messagesSent
ch <- messagesErrored
}
10. 将接口调用逻辑从第6步移到 Collect 函数中
直接将采集的数据发送到 prometheus.Metric 通道中。
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,
)
e.HitMirthRestApisAndUpdateMetrics(channelIdNameMap, ch)
}
当执行 api 调用时，确保使用prometheus.MustNewConstMetric(prometheus.Desc, metric type, measurement)发送测量值，如果你需要传入额外的标签，可以像下面这样在参数列表的后面加入：
channelError, _ := strconv.ParseFloat(channelStatsList.Channels[i].Error, 64)
ch <- prometheus.MustNewConstMetric(
messagesErrored, prometheus.GaugeValue, channelError, channelName,
)
11. 在 main 函数中声明 exporter
代码语言：javascript复制exporter := NewExporter(mirthEndpoint, mirthUsername, mirthPassword)
prometheus.MustRegister(exporter)
到这里其实这个 Exporter 就可以使用了，每次访问 metrics 路由的时候，它会执行 api 调用，并以 Prometheus Text 文本格式返回数据。下面的步骤主要是方便部署了。
12. 将硬编码的 api 路径放到 flag 中
前面我们硬编码了好多参数，比如应用程序的网址、metrics 路由地址以及 exporter 端口，我们可以通过从命令行参数中来解析这些值使程序更加灵活。
代码语言：javascript复制var (
listenAddress = flag.String("web.listen-address", ":9141",
"Address to listen on for telemetry")
metricsPath = flag.String("web.telemetry-path", "/metrics",
"Path under which to expose metrics")
)
func main() {
flag.Parse()
...
http.Handle(*metricsPath, promhttp.Handler())
log.Fatal(http.ListenAndServe(*listenAddress, nil))
}
13. 将凭证放入环境变量
如果应用端点改变了或者登录凭证改变了怎么办？我们可以从环境变量中来加载这些数据，在这个例子中，我们使用 godotenv 这个包来帮助将变量值存储在本地的一个目录中：
代码语言：javascript复制import (
"os"
)
func main() {
err := godotenv.Load()
if err != nil {
log.Println("Error loading .env file, assume env variables are set.")
}
mirthEndpoint := os.Getenv("MIRTH_ENDPOINT")
mirthUsername := os.Getenv("MIRTH_USERNAME")
mirthPassword := os.Getenv("MIRTH_PASSWORD")
}
整个 Exporter 完整的代码如下所示：
代码语言：javascript复制package main
import (
"crypto/tls"
"encoding/xml"
"flag"
"io/ioutil"
"log"
"net/http"
"os"
"strconv"
"github.com/joho/godotenv"
"github.com/prometheus/client_golang/prometheus"
"github.com/prometheus/client_golang/prometheus/promhttp"
)
/*
<map>
<entry>
<string>101af57f-f26c-40d3-86a3-309e74b93512</string>
<string>Send-Email-Notification</string>
</entry>
</map>
*/
type ChannelIdNameMap struct {
XMLName xml.Name `xml:"map"`
Entries []ChannelEntry `xml:"entry"`
}
type ChannelEntry struct {
XMLName xml.Name `xml:"entry"`
Values []string `xml:"string"`
}
/*
<list>
<channelStatistics>
<serverId>c5e6a736-0e88-46a7-bf32-5b4908c4d859</serverId>
<channelId>101af57f-f26c-40d3-86a3-309e74b93512</channelId>
<received>0</received>
<sent>0</sent>
<error>0</error>
<filtered>0</filtered>
<queued>0</queued>
</channelStatistics>
</list>
*/
type ChannelStatsList struct {
XMLName xml.Name `xml:"list"`
Channels []ChannelStats `xml:"channelStatistics"`
}
type ChannelStats struct {
XMLName xml.Name `xml:"channelStatistics"`
ServerId string `xml:"serverId"`
ChannelId string `xml:"channelId"`
Received string `xml:"received"`
Sent string `xml:"sent"`
Error string `xml:"error"`
Filtered string `xml:"filtered"`
Queued string `xml:"queued"`
}
const namespace = "mirth"
const channelIdNameApi = "/api/channels/idsAndNames"
const channelStatsApi = "/api/channels/statistics"
var (
tr = &http.Transport{
TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
}
client = &http.Client{Transport: tr}
listenAddress = flag.String("web.listen-address", ":9141",
"Address to listen on for telemetry")
metricsPath = flag.String("web.telemetry-path", "/metrics",
"Path under which to expose metrics")
// 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,
)
)
type Exporter struct {
mirthEndpoint, mirthUsername, mirthPassword string
}
func NewExporter(mirthEndpoint string, mirthUsername string, mirthPassword string) *Exporter {
return &Exporter{
mirthEndpoint: mirthEndpoint,
mirthUsername: mirthUsername,
mirthPassword: mirthPassword,
}
}
func (e *Exporter) Describe(ch chan<- *prometheus.Desc) {
ch <- up
ch <- messagesReceived
ch <- messagesFiltered
ch <- messagesQueued
ch <- messagesSent
ch <- messagesErrored
}
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,
)
e.HitMirthRestApisAndUpdateMetrics(channelIdNameMap, ch)
}
func (e *Exporter) LoadChannelIdNameMap() (map[string]string, error) {
// Create the map of channel id to names
channelIdNameMap := make(map[string]string)
req, err := http.NewRequest("GET", e.mirthEndpoint channelIdNameApi, nil)
if err != nil {
return nil, err
}
// This one line implements the authentication required for the task.
req.SetBasicAuth(e.mirthUsername, e.mirthPassword)
// Make request and show output.
resp, err := client.Do(req)
if err != nil {
return nil, err
}
body, err := ioutil.ReadAll(resp.Body)
resp.Body.Close()
if err != nil {
return nil, err
}
// fmt.Println(string(body))
// we initialize our array
var channelIdNameMapXML ChannelIdNameMap
// we unmarshal our byteArray which contains our
// xmlFiles content into 'users' which we defined above
err = xml.Unmarshal(body, &channelIdNameMapXML)
if err != nil {
return nil, err
}
for i := 0; i < len(channelIdNameMapXML.Entries); i {
channelIdNameMap[channelIdNameMapXML.Entries[i].Values[0]] = channelIdNameMapXML.Entries[i].Values[1]
}
return channelIdNameMap, nil
}
func (e *Exporter) HitMirthRestApisAndUpdateMetrics(channelIdNameMap map[string]string, ch chan<- prometheus.Metric) {
// Load channel stats
req, err := http.NewRequest("GET", e.mirthEndpoint channelStatsApi, nil)
if err != nil {
log.Fatal(err)
}
// This one line implements the authentication required for the task.
req.SetBasicAuth(e.mirthUsername, e.mirthPassword)
// Make request and show output.
resp, err := client.Do(req)
if err != nil {
log.Fatal(err)
}
body, err := ioutil.ReadAll(resp.Body)
resp.Body.Close()
if err != nil {
log.Fatal(err)
}
// fmt.Println(string(body))
// we initialize our array
var channelStatsList ChannelStatsList
// we unmarshal our byteArray which contains our
// xmlFiles content into 'users' which we defined above
err = xml.Unmarshal(body, &channelStatsList)
if err != nil {
log.Fatal(err)
}
for i := 0; i < len(channelStatsList.Channels); i {
channelName := channelIdNameMap[channelStatsList.Channels[i].ChannelId]
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,
)
}
log.Println("Endpoint scraped")
}
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(`<html>
<head><title>Mirth Channel Exporter</title></head>
<body>
<h1>Mirth Channel Exporter</h1>
<p><a href='` *metricsPath `'>Metrics</a></p>
</body>
</html>`))
})
log.Fatal(http.ListenAndServe(*listenAddress, nil))
}
14. 编写一个 Makefile 文件，方便在不同平台上快速构建
Makefile 可以让你在开发过程中省去很多多余的操作，比如我们要构建多个平台的构建程序，可以创建如下所示的 Makefile 文件。
代码语言：javascript复制linux:
GOOS=linux GOARCH=amd64 go build
mac:
GOOS=darwin GOARCH=amd64 go build
只要调用 make mac 或 make linux 命令就可以看到不同的可执行文件出现。
15. 编写一个 service 文件，将这个 go 应用作为守护进程运行
我们可以为这个 Exporter 编写一个 service 文件或者 Dockerfile 文件来管理该应用，比如这里我们直接在 Centos 7 上用 systemd 来管理该应用。这可以编写一个如下所示的 service 文件：
代码语言：javascript复制[Unit]
Description=mirth channel exporter
After=network.target
StartLimitIntervalSec=0
[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
到这里就完成了使用 Golang 编写一个简单的 Prometheus Exporter。
“原文链接：https://medium.com/teamzerolabs/15-steps-to-write-an-application-prometheus-exporter-in-go-9746b4520e26 ”
