How hot restart implemented Go

Hot restart

Warm restart (Zero Downtime), refers to the old and new process seamless handover , during the replacement of the client's service can be maintained.

principle

Parent monitor the restart signal
After receiving the restart signal, the parent calls fork , passing socket the descriptor to the child process
Receiving a child process and the parent process listens transfer socket descriptor
After the child process is started successfully, the parent process to stop receiving new connections, while waiting for the old connection process is completed (or overtime)
Parent process to exit, hot restart is completed

achieve

package main

import (
    "context"
    "errors"
    "flag" "log" "net" "net/http" "os" "os/exec" "os/signal" "syscall" "time" ) var ( server *http.Server listener net.Listener = nil graceful = flag.Bool("graceful", false, "listen on fd open 3 (internal use only)") message = flag.String("message", "Hello World", "message to send") ) func handler(w http.ResponseWriter, r *http.Request) { time.Sleep(5 * time.Second) w.Write([]byte(*message)) } func main() { var err error // 解析参数 flag.Parse() http.HandleFunc("/test", handler) server = &http.Server{Addr: ":3000"} // 设置监听器的监听对象（新建的或已存在的 socket 描述符） if *graceful { // 子进程监听父进程传递的 socket 描述符 log.Println("listening on the existing file descriptor 3") // 子进程的 0, 1, 2 是预留给标准输入、标准输出、错误输出，故传递的 socket 描述符 // 应放在子进程的 3 f := os.NewFile(3, "") listener, err = net.FileListener(f) } else { // 父进程监听新建的 socket 描述符 log.Println("listening on a new file descriptor") listener, err = net.Listen("tcp", server.Addr) } if err != nil { log.Fatalf("listener error: %v", err) } go func() { err = server.Serve(listener) log.Printf("server.Serve err: %v\n", err) }() // 监听信号 handleSignal() log.Println("signal end") } func handleSignal() { ch := make(chan os.Signal, 1) // 监听信号 signal.Notify(ch, syscall.SIGINT, syscall.SIGTERM, syscall.SIGUSR2) for { sig := <-ch log.Printf("signal receive: %v\n", sig) ctx, _ := context.WithTimeout(context.Background(), 20*time.Second) switch sig { case syscall.SIGINT, syscall.SIGTERM: // 终止进程执行 log.Println("shutdown") signal.Stop(ch) server.Shutdown(ctx) log.Println("graceful shutdown") return case syscall.SIGUSR2: // 进程热重启 log.Println("reload") err := reload() // 执行热重启函数 if err != nil { log.Fatalf("graceful reload error: %v", err) } server.Shutdown(ctx) log.Println("graceful reload") return } } } func reload() error { tl, ok := listener.(*net.TCPListener) if !ok { return errors.New("listener is not tcp listener") } // 获取 socket 描述符 f, err := tl.File() if err != nil { return err } // 设置传递给子进程的参数（包含 socket 描述符） args := []string{"-graceful"} cmd := exec.Command(os.Args[0], args...) cmd.Stdout = os.Stdout // 标准输出 cmd.Stderr = os.Stderr // 错误输出 cmd.ExtraFiles = []*os.File{f} // 文件描述符 // 新建并执行子进程 return cmd.Start() }

We run a parent process cmd.ExtraFiles = []*os.File{f} to pass socket the descriptor to the child process, the child process by executing f := os.NewFile(3, "") to get the descriptor. Notably, the child process 0 , 1 and 2 are reserved for standard input, standard output, and error output, the parent process transfer socket descriptors from the order of the sub process is 3 started.

test

Compile the above program is main executed ./main -message "Graceful Reload" , access http://localhost:3000/test , wait five seconds, we can see Graceful Reload the response.

By executing kill -USR2 [PID] , we can carry out Graceful Reload tests.

By executing kill -INT [PID] , we can carry out Graceful Shutdown tests.

Hot restart

principle

achieve

test

Reference material

Guess you like