Server Logging with Winston

A Practical Guide to using Winston

Server Logging with Winston

by John Vincent


Posted on May 15, 2017



Winston Logging for an Express App

Logging has many challenges. It is very important to be able to get the right logging messages for any given situation.

NPM Winston

Winston at npm

npm install winston --save

Goals

The following are the goals

  • Ensure all log messages are handled.
  • Development environment where all messages are saved to console and log file.
  • Heroku environment where info, warn and error messages are saved to console.
  • Production environment (Digital Ocean) where info, warn and error messages are saved to log file.

Configuration

Thus, the following information needs to be outside of the application

  • Log level
  • Environment
  • Logging file

I have chosen the following

  • Log Level = LOG_LEVEL
    • Development environment; debug
    • Heroku environment; info
    • Production environment; info
  • Environment = LOG_ENV
    • Development environment; dev
    • Heroku environment; heroku
    • Production environment; production
  • Logging file = LOG_FILE
    • Development environment; log file must be outside of workspace else it interferes with Nodemon.
    • Production environment; with other log files.

Note that LOG_LEVEL is independent. This is to allow for the setting of higher debug levels in a production environment. This may be required if in pursuit of a production problem.

Configuration Data

I have chosen to store in .env file. For example

LOG_LEVEL=debug
LOG_ENV=dev
# LOG_ENV=heroku
# LOG_ENV=prod
LOG_FILE=/Users/{logs}/tmp/logfile.txt

Loading Configuration Data

Start with server.js

const express = require('express');
const mongoose = require('mongoose');

const {PORT, DATABASE_URL} = require('./config/config');

const {logger} = require('./config/logger');

...

require('./config/middleware.express')(app);
logger.info('Application middleware is configured');

require('./config/routes')(app);
logger.info('Application routes have been loaded');

module.exports = {app, runServer, closeServer};
logger.info('Application is exported');

To load configuration data, config.js

require('dotenv').config();

exports.LOG_ENV = process.env.LOG_ENV || 'prod';

exports.LOG_LEVEL = process.env.LOG_LEVEL || 'info';

exports.LOG_FILE = process.env.LOG_FILE || 'logfile.txt';

Logger

As I needed many different instances of a logger, I rolled my own

const winston = require('winston');

const {LOG_LEVEL, LOG_ENV, LOG_FILE} = require('./config');

const consoleOptions = {
    level: LOG_LEVEL,
    handleExceptions: true,
    // json: true,
    colorize: true
};
const fileOptions = {
    level: LOG_LEVEL,
    filename: LOG_FILE,
    handleExceptions: true,
    // json: true,
    colorize: true
};

const logger = (function() {
    if (LOG_ENV === 'production') {
        return new(winston.Logger)({
            transports: [
                new (winston.transports.File)(fileOptions)
            ]
        });
    }
    else if (LOG_ENV === 'heroku') {
        return new(winston.Logger)({
            transports: [
                new(winston.transports.Console)(consoleOptions)
            ]
        });
    }
    return new(winston.Logger)({        // dev
        transports: [
            new(winston.transports.Console)(consoleOptions),
            new (winston.transports.File)(fileOptions)
        ]
    });
}());

logger.stream = {
    write: (message, encoding) => {
        logger.debug(message);
    }
};

module.exports = {
    logger
};

Thus, when the server starts, the correct logger is configured.

Usage

Add to list of requires

@requires logger

Get a reference

const {logger} = require('./config/logger');

Convention

I have chosen the following

  • logger.info
    • when something happens, examples
      • Server starts or stops
      • Email sent
      • Record added/updated/deleted
      • Event
      • Useful running message
  • logger.debug
    • traces only
      • careful to ensure no pid
  • logger.error
    • error events of any kind
      • ensure full details
  • logger.warn
    • not an error but may be important, for example
      • record should have been found but was not.
      • could not find a URL that should have existed.
      • problems reading from a URL, for example, RSS feed.

Morgan

For an Express app, I also use Morgan to log HTTP requests.

I wish to stream Morgan logging messages to Winston.

As shown above, server.js

...

require('./config/middleware.express')(app);
logger.info('Application middleware is configured');

...

Morgan is middleware and so is loaded by middleware.express.js. Only the essentials are shown

const morgan = require('morgan');
const {logger} = require('./logger');
app.use(morgan('common', {stream: logger.stream}));

Thus Morgan messages will use logger.stream

logger.stream = {
    write: (message, encoding) => {
        logger.debug(message);
    }
};

which uses Winston logging to stream Morgan logging at level ‘debug’.

Browser Logs

A simple trick to turn off console.log messages in the browser

globals.js

var hasConsole = false;
if (!hasConsole) {
  console.log = function() {};
}

globals.js is the first thing invoked.