Local Filesystem Hook for Logrus

Sometimes developers like to write directly to a file on the filesystem. This is a hook for logrus which designed to allow users to do that. The log levels are dynamic at instantiation of the hook, so it is capable of logging at some or all levels.

Example

import (
	"github.com/rifflock/lfshook"
	"github.com/sirupsen/logrus"
)

var Log *logrus.Logger

func NewLogger() *logrus.Logger {
	if Log != nil {
		return Log
	}

	pathMap := lfshook.PathMap{
		logrus.InfoLevel:  "/var/log/info.log",
		logrus.ErrorLevel: "/var/log/error.log",
	}

	Log = logrus.New()
	Log.Hooks.Add(lfshook.NewHook(
		pathMap,
		&logrus.JSONFormatter{},
	))
	return Log
}

Formatters

lfshook will strip colors from any TextFormatter type formatters when writing to local file, because the color codes don't look great in file.

If no formatter is provided via lfshook.NewHook, a default text formatter will be used.

Log rotation

In order to enable automatic log rotation it's possible to provide an io.Writer instead of the path string of a log file. In combination with packages like file-rotatelogs log rotation can easily be achieved.

package main

import (
	rotatelogs "github.com/lestrrat-go/file-rotatelogs"
	"github.com/rifflock/lfshook"
	"github.com/sirupsen/logrus"
)

var Log *logrus.Logger

func NewLogger() *logrus.Logger {
	if Log != nil {
		return Log
	}

	path := "/var/log/go.log"
	writer := rotatelogs.New(
		path+".%Y%m%d%H%M",
		rotatelogs.WithLinkName(path),
		rotatelogs.WithMaxAge(time.Duration(86400)*time.Second),
		rotatelogs.WithRotationTime(time.Duration(604800)*time.Second),
	)

	logrus.Hooks.Add(lfshook.NewHook(
		lfshook.WriterMap{
			logrus.InfoLevel:  writer,
			logrus.ErrorLevel: writer,
		},
		&logrus.JSONFormatter,
	))

	Log = logrus.New()
	Log.Hooks.Add(lfshook.NewHook(
		pathMap,
		&logrus.JSONFormatter{},
	))

	return Log
}

Note:

User who run the go application must have read/write permissions to the selected log files. If the files do not exists yet, then user must have permission to the target directory.