Using Air for Hot Reload in Go Applications: Installation, Configuration, and Advanced Features

During development, hot‑reload technology greatly improves experience by automatically restarting a Go application when source files change, saving time and effort. Air is a command‑line utility designed for Go that provides this capability.

Quick Start

Installation : run $ go install github.com/air-verse/air@latest . The tool is installed via the Go toolchain, so no version is specified; the latest version is used.

Project structure :

$ tree -F fly
fly/
├── README.md
└── main.go

Example code (main.go) :

package main

import (
    "fmt"
    "net/http"
    "os"
    "os/signal"
    "syscall"
)

func main() {
    signalChan := make(chan os.Signal, 1)
    signal.Notify(signalChan, syscall.SIGINT, syscall.SIGTERM)

    server := &http.Server{Addr: ":8080"}
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        fmt.Fprintf(w, "🚀 Hello Air! (PID: %d)", os.Getpid())
    })
    go func() {
        fmt.Printf("Server started at http://localhost:8080 (PID: %d)\n", os.Getpid())
        if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
            fmt.Printf("Server error: %v\n", err)
        }
    }()
    <-signalChan
    fmt.Println("Server shutting down...")
    server.Close()
}

Running air in the project root starts the server; modifying main.go triggers an automatic restart, changing the PID and response content.

Full Configuration

Air uses a TOML file ( .air.toml ) with sections such as [build] , [log] , [color] , [misc] , [screen] , and [proxy] . Key fields include:

root – project working directory.

tmp_dir – temporary files.

cmd – build command (e.g., go build -o ./tmp/main . ).

bin – path to the compiled binary.

full_bin – binary with environment variables.

args_bin – arguments passed to the binary (e.g., ["hello", "world"] ).

Various include/exclude patterns for files and directories.

Logging, color, and screen‑clear options.

Only the most frequently used options ( cmd , bin , args_bin , full_bin ) need to be customized for typical projects.

Advanced Usage

To ensure graceful shutdown logs appear, enable send_interrupt = true and set kill_delay = "1s" in the [build] section. Air will then send a Ctrl+C signal to the Go process and wait the specified delay before terminating.

Command‑line flags can override configuration values. For example, air -build.args_bin xxx runs the program with argument xxx . When both a flag and a config entry are provided, the flag takes precedence, as demonstrated by running air -build.args_bin xxx -c .air.toml .

Conclusion

Hot‑reload with Air speeds up Go development, requires only a single air command to start, and offers flexible configuration via TOML files or CLI flags. It is recommended for backend Go projects seeking rapid iteration.