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Gin Web Framework

How to write log file

Writing logs to a file is essential for production applications where you need to retain request history for debugging, auditing, or monitoring. By default, Gin writes all log output to os.Stdout. You can redirect this by setting gin.DefaultWriter before creating the router.

package main


import (
  "io"
  "os"


  "github.com/gin-gonic/gin"
)


func main() {
    // Disable Console Color, you don't need console color when writing the logs to file.
    gin.DisableConsoleColor()


    // Logging to a file.
    f, _ := os.Create("gin.log")
    gin.DefaultWriter = io.MultiWriter(f)


    // Use the following code if you need to write the logs to file and console at the same time.
    // gin.DefaultWriter = io.MultiWriter(f, os.Stdout)


    router := gin.Default()
    router.GET("/ping", func(c *gin.Context) {
        c.String(200, "pong")
    })


    router.Run(":8080")
}

Writing to both file and console

The io.MultiWriter function from Go’s standard library accepts multiple io.Writer values and duplicates writes to all of them. This is useful during development when you want to see logs in the terminal while also persisting them to disk:

f, _ := os.Create("gin.log")
gin.DefaultWriter = io.MultiWriter(f, os.Stdout)

With this setup, every log entry is written to both gin.log and the console simultaneously.

Log rotation in production

The example above uses os.Create, which truncates the log file each time the application starts. In production, you typically want to append to existing logs and rotate files based on size or time. Consider using a log rotation library such as lumberjack:

import "gopkg.in/natefinch/lumberjack.v2"


func main() {
    gin.DisableConsoleColor()


    gin.DefaultWriter = &lumberjack.Logger{
        Filename:   "gin.log",
        MaxSize:    100, // megabytes
        MaxBackups: 3,
        MaxAge:     28, // days
    }


    router := gin.Default()
    router.GET("/ping", func(c *gin.Context) {
        c.String(200, "pong")
    })


    router.Run(":8080")
}

See also