Logging Utility

Opinionated logging utility for unified logging in distributed systems based on winston.

• Logging Utility
• Install
• Configuration
• Usage
  • Logging Middlewares
    • Express

Install

Install via npm:

npm install --save @martinnirtl/logging

Or yarn:

yarn add @martinnirtl/logging

Configuration

Programmatically configure library:

import logger, { setDefaults } from '@martinnirtl/logging'

setDefaults({
  level: 'warn',
  metadata: { service: 'foo-service' },
  prettyPrint: process.env.NODE_ENV !== 'production',
})

logger.info('hello world') // will not be printed

Or use environment variables:

# Specify log-level (default: info, options: [silly, debug, info, warn, error])
LOG_LEVEL=debug

# Add metadata tags with `LOG_METADATA_`-prefix, e.g. set { service: 'foo-service' }
LOG_METADATA_SERVICE=foo-service

# Pretty-print json-logs on truthy value (default: false)
LOG_PRETTY=true

# Silent logger on truthy value (default: false)
LOG_SILENT=0

Usage

Singleton pattern:

import logger, { setDefaults } from '@martinnirtl/logging'

setDefaults({
  level: 'debug',
  metadata: { 'process-id': process.pid },
})

logger.debug('just set the logger-defaults')

logger.info('starting application...', { date: new Date() })

Or dedicated loggers:

import { getLogger, setDefaults } from '@martinnirtl/logging'

setDefaults({
  level: 'debug',
  metadata: { service: 'foo-service' },
})

const logger = getLogger({
  metadata: { context: 'initialization' },
})

logger.info('starting application...', { date: new Date() })

Logging Middlewares

The lib also ships middlewares to optimally integrate into popular 3rd party frameworks.

At the moment, only the express framework is supported.

Express

The express middleware allows to add a logger instance to every request-handler. Also it enables logging of incoming requests plus automatic request-body|headers|query|params to logging object's metadata mapping.

const { getLogger, middleware, setDefaults } = require('@martinnirtl/logging')
const express = require('express')

setDefaults({
  level: 'debug', // default 'info'
})

const logger = getLogger({
  metadata: { context: 'init' },
})

const app = express()

app.use(middleware('express', {
  addToRequestObject: true, // default true
  logIncoming: {
    level: "debug", // default 'info'
    metadata: {
      body: true, // add body as a whole
      headers: ['host'], // add host field of headers to metadata
    }
  }
}))

app.all('/', (req, res) => {
  req.logger.debug('it works!')

  return res.status(200).send('Hello World')
})

app.listen(3000, () => logger.info(`app listening on port 3000`))