Golang学习之平滑重启

脚本专栏 2025/10/27 佚名

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在上一篇博客介绍TOML配置的时候，讲到了通过信号通知重载配置。我们在这一篇中介绍下如何的平滑重启server。

与重载配置相同的是我们也需要通过信号来通知server重启，但关键在于平滑重启，如果只是简单的重启，只需要kill掉，然后再拉起即可。平滑重启意味着server升级的时候可以不用停止业务。

我们先来看下Github上有没有相应的库解决这个问题，然后找到了如下三个库：

facebookgo/grace - Graceful restart & zero downtime deploy for Go servers.
fvbock/endless - Zero downtime restarts for go servers (Drop in replacement for http.ListenAndServe)
jpillora/overseer - Monitorable, gracefully restarting, self-upgrading binaries in Go (golang)

我们分别来学习一下，下面只讲解http server的重启。

使用方式

我们来分别使用这三个库来做平滑重启的事情，之后来对比其优缺点。

这三个库的官方都给了相应的例子，例子如下：

但三个库官方的例子不太一致，我们来统一一下：

grace例子 https://github.com/facebookgo/grace/blob/master/gracedemo/demo.go
endless例子 https://github.com/fvbock/endless/tree/master/examples
overseer例子 https://github.com/jpillora/overseer/tree/master/example

我们参考官方的例子分别来写下用来对比的例子：

grace

package main

import (
  "time"
  "net/http"
  "github.com/facebookgo/grace/gracehttp"
)

func main() {
  gracehttp.Serve(
    &http.Server{Addr: ":5001", Handler: newGraceHandler()},
    &http.Server{Addr: ":5002", Handler: newGraceHandler()},
  )
}

func newGraceHandler() http.Handler {
  mux := http.NewServeMux()
  mux.HandleFunc("/sleep", func(w http.ResponseWriter, r *http.Request) {
    duration, err := time.ParseDuration(r.FormValue("duration"))
    if err != nil {
      http.Error(w, err.Error(), 400)
      return
    }
    time.Sleep(duration)
    w.Write([]byte("Hello World"))
  })
  return mux
}

endless

package main

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

  "github.com/fvbock/endless"
  "github.com/gorilla/mux"
)

func handler(w http.ResponseWriter, r *http.Request) {
  duration, err := time.ParseDuration(r.FormValue("duration"))
  if err != nil {
    http.Error(w, err.Error(), 400)
    return
  }
  time.Sleep(duration)
  w.Write([]byte("Hello World"))
}

func main() {
  mux1 := mux.NewRouter()
  mux1.HandleFunc("/sleep", handler)

  w := sync.WaitGroup{}
  w.Add(2)
  go func() {
    err := endless.ListenAndServe(":5003", mux1)
    if err != nil {
      log.Println(err)
    }
    log.Println("Server on 5003 stopped")
    w.Done()
  }()
  go func() {
    err := endless.ListenAndServe(":5004", mux1)
    if err != nil {
      log.Println(err)
    }
    log.Println("Server on 5004 stopped")
    w.Done()
  }()
  w.Wait()
  log.Println("All servers stopped. Exiting.")

  os.Exit(0)
}

overseer

package main

import (
  "fmt"
  "net/http"
  "time"

  "github.com/jpillora/overseer"
)

//see example.sh for the use-case

// BuildID is compile-time variable
var BuildID = "0"

//convert your 'main()' into a 'prog(state)'
//'prog()' is run in a child process
func prog(state overseer.State) {
  fmt.Printf("app#%s (%s) listening...\n", BuildID, state.ID)
  http.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    duration, err := time.ParseDuration(r.FormValue("duration"))
    if err != nil {
      http.Error(w, err.Error(), 400)
      return
    }
    time.Sleep(duration)
    w.Write([]byte("Hello World"))
    fmt.Fprintf(w, "app#%s (%s) says hello\n", BuildID, state.ID)
  }))
  http.Serve(state.Listener, nil)
  fmt.Printf("app#%s (%s) exiting...\n", BuildID, state.ID)
}

//then create another 'main' which runs the upgrades
//'main()' is run in the initial process
func main() {
  overseer.Run(overseer.Config{
    Program: prog,
    Addresses: []string{":5005", ":5006"},
    //Fetcher: &fetcher.File{Path: "my_app_next"},
    Debug:  false, //display log of overseer actions
  })
}

对比

对比示例的操作步骤

分别构建上面的示例，并记录pid
调用API，在其未返回时，修改内容(Hello World -> Hello Harry)，重新构建。查看旧API是否返回旧的内容
调用新API，查看返回的内容是否是新的内容
查看当前运行的pid，是否与之前一致

下面给一下操作命令

# 第一次构建项目
go build grace.go
# 运行项目，这时就可以做内容修改了
./grace &
# 请求项目，60s后返回
curl "http://127.0.0.1:5001/sleep" &
# 再次构建项目，这里是新内容
go build grace.go
# 重启，2096为pid
kill -USR2 2096
# 新API请求
curl "http://127.0.0.1:5001/sleep"


# 第一次构建项目
go build endless.go
# 运行项目，这时就可以做内容修改了
./endless &
# 请求项目，60s后返回
curl "http://127.0.0.1:5003/sleep" &
# 再次构建项目，这里是新内容
go build endless.go
# 重启，22072为pid
kill -1 22072
# 新API请求
curl "http://127.0.0.1:5003/sleep"


# 第一次构建项目
go build -ldflags '-X main.BuildID=1' overseer.go
# 运行项目，这时就可以做内容修改了
./overseer &
# 请求项目，60s后返回
curl "http://127.0.0.1:5005/sleep" &
# 再次构建项目，这里是新内容，注意版本号不同了
go build -ldflags '-X main.BuildID=2' overseer.go
# 重启，28300为主进程pid
kill -USR2 28300
# 新API请求
curl http://127.0.0.1:5005/sleep"text-align: center">
自己实现
我们下面来尝试自己实现下第一种处理，代码如下，代码来自《热重启golang服务器》：




package main
import (
  "context"
  "errors"
  "flag"
  "log"
  "net"
  "net/http"
  "os"
  "os/exec"
  "os/signal"
  "syscall"
  "time"
)

var (
  server  *http.Server
  listener net.Listener
  graceful = flag.Bool("graceful", false, "listen on fd open 3 (internal use only)")
)

func sleep(w http.ResponseWriter, r *http.Request) {
  duration, err := time.ParseDuration(r.FormValue("duration"))
  if err != nil {
    http.Error(w, err.Error(), 400)
    return
  }
  time.Sleep(duration)
  w.Write([]byte("Hello World"))
}

func main() {
  flag.Parse()

  http.HandleFunc("/sleep", sleep)
  server = &http.Server{Addr: ":5007"}

  var err error
  if *graceful {
    log.Print("main: Listening to existing file descriptor 3.")
    // cmd.ExtraFiles: If non-nil, entry i becomes file descriptor 3+i.
    // when we put socket FD at the first entry, it will always be 3(0+3)
    f := os.NewFile(3, "")
    listener, err = net.FileListener(f)
  } else {
    log.Print("main: Listening on a new file descriptor.")
    listener, err = net.Listen("tcp", server.Addr)
  }

  if err != nil {
    log.Fatalf("listener error: %v", err)
  }

  go func() {
    // server.Shutdown() stops Serve() immediately, thus server.Serve() should not be in main goroutine
    err = server.Serve(listener)
    log.Printf("server.Serve err: %v\n", err)
  }()
  signalHandler()
  log.Printf("signal end")
}

func reload() error {
  tl, ok := listener.(*net.TCPListener)
  if !ok {
    return errors.New("listener is not tcp listener")
  }

  f, err := tl.File()
  if err != nil {
    return err
  }

  args := []string{"-graceful"}
  cmd := exec.Command(os.Args[0], args...)
  cmd.Stdout = os.Stdout
  cmd.Stderr = os.Stderr
  // put socket FD at the first entry
  cmd.ExtraFiles = []*os.File{f}
  return cmd.Start()
}

func signalHandler() {
  ch := make(chan os.Signal, 1)
  signal.Notify(ch, syscall.SIGINT, syscall.SIGTERM, syscall.SIGUSR2)
  for {
    sig := <-ch
    log.Printf("signal: %v", sig)

    // timeout context for shutdown
    ctx, _ := context.WithTimeout(context.Background(), 100*time.Second)
    switch sig {
    case syscall.SIGINT, syscall.SIGTERM:
      // stop
      log.Printf("stop")
      signal.Stop(ch)
      server.Shutdown(ctx)
      log.Printf("graceful shutdown")
      return
    case syscall.SIGUSR2:
      // reload
      log.Printf("reload")
      err := reload()
      if err != nil {
        log.Fatalf("graceful restart error: %v", err)
      }
      server.Shutdown(ctx)
      log.Printf("graceful reload")
      return
    }
  }
}


代码可参考：https://github.com/CraryPrimitiveMan/go-in-action/tree/master/ch4
关于这一部分，个人的理解也不是特别深入，如果又不正确的地方请大家指正。
参考文章
热重启golang服务器 


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