How do I hot-reload configuration at runtime in Go?

Hot-reloading configuration at runtime in Go can significantly enhance the flexibility of applications. This technique allows you to modify configuration settings without the need to restart the application. Below is an example demonstrating how to implement this feature using Go's file watching capabilities.


package main

import (
    "encoding/json"
    "fmt"
    "github.com/fsnotify/fsnotify"
    "io/ioutil"
    "log"
    "os"
    "time"
)

type Config struct {
    AppName string `json:"app_name"`
    Port    int    `json:"port"`
}

var config Config

func loadConfig() {
    file, err := os.Open("config.json")
    if err != nil {
        log.Fatalf("Failed to open config file: %s", err)
    }
    defer file.Close()

    byteValue, _ := ioutil.ReadAll(file)
    json.Unmarshal(byteValue, &config)

    fmt.Printf("Config loaded: %+v\n", config)
}

func watchConfig(path string) {
    watcher, err := fsnotify.NewWatcher()
    if err != nil {
        log.Fatal(err)
    }
    defer watcher.Close()

    err = watcher.Add(path)
    if err != nil {
        log.Fatal(err)
    }

    done := make(chan bool)
    go func() {
        for {
            select {
            case event, ok := <-watcher.Events:
                if !ok {
                    return
                }
                if event.Op&fsnotify.Write == fsnotify.Write {
                    fmt.Println("Config file modified, reloading...")
                    loadConfig()
                }
            case err, ok := <-watcher.Errors:
                if !ok {
                    return
                }
                log.Println("Error:", err)
            }
        }
    }()
    <-done
}

func main() {
    loadConfig()
    go watchConfig("config.json")

    // Simulated application running
    for {
        time.Sleep(10 * time.Second)
    }
}

hot-reload configuration runtime Go fsnotify json file watching

How do I hot-reload configuration at runtime in Go?

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How do I hot-reload configuration at runtime in Go?

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