go - 如何在数据库更改时重新评估 promhttp.Handler？

Question

我可能在滥用 promhttp.Handler() 来实现我的微服务的用例，告诉我:

• 版本
• 如果它有数据库连接

如果有更好的方法来监控我的微服务，请告诉我!

我不确定如何以这样一种方式构造句柄，即在调用/metrics 时，db.Ping()重新评估。

https://s.natalian.org/2019-06-02/msping.mp4

package main

import (
    "log"
    "net/http"
    "os"

    _ "github.com/go-sql-driver/mysql"
    "github.com/gorilla/mux"
    "github.com/jmoiron/sqlx"
    "github.com/prometheus/client_golang/prometheus"
    "github.com/prometheus/client_golang/prometheus/promhttp"
)

const version = "0.0.1"

type App struct {
    Router *mux.Router
    DB     *sqlx.DB
}

func main() {
    a := App{}
    a.Initialize()

    log.Fatal(http.ListenAndServe(":"+os.Getenv("PORT"), a.Router))
}

func (a *App) Initialize() {
    connectionString := "root:secret@tcp(localhost:3306)/rest_api_example?multiStatements=true&sql_mode=TRADITIONAL&timeout=5s"
    var err error
    a.DB, err = sqlx.Open("mysql", connectionString)
    if err != nil {
        log.Fatal(err)
    }

    microservicecheck := prometheus.NewGaugeVec(
        prometheus.GaugeOpts{
            Name: "mscheck",
            Help: "Version with DB ping check",
        },
        []string{
            "commit",
        },
    )

    if a.DB.Ping() == nil {
        microservicecheck.WithLabelValues(version).Set(1)
    } else {
        microservicecheck.WithLabelValues(version).Set(0)
    }

    prometheus.MustRegister(microservicecheck)

    a.Router = mux.NewRouter()
    a.initializeRoutes()
}

func (a *App) initializeRoutes() {
    a.Router.Handle("/metrics", promhttp.Handler()).Methods("GET")
}

https://play.golang.org/p/9DdXnz77S55

Answer 1

您还可以添加一个执行 preflight routine 的中间件 Hook (即您的 ping 测试)在调用 promhttp.Handler() 之前。但是，在收集时，我认为应该已经统计了指标；而不是在收集实例中生成。所以……

尝试一个单独的 go-routine，它将定期轮询数据库连接的健康状况。这避免了任何困惑的 Hook 或自定义收集器:

var pingPollingFreq = 5 * time.Second // this should probably match the Prometheus scrape interval

func (a *App) Initialize() {       
    // ...

    prometheus.MustRegister(microservicecheck)

    go func() {
        for {
            if a.DB.Ping() == nil {
                microservicecheck.WithLabelValues(version).Set(1)
            } else {
                microservicecheck.WithLabelValues(version).Set(0)
            }
            time.Sleep(pingPollingFreq)
        }
    }()

    // ...
}