logger.js

const winston = require('winston'),
  moment = require('moment'),
  config = require('../../config/config').config,
  getNamespace = require('cls-hooked').getNamespace;

exports.logger = new winston.Logger({
  transports: [
    new winston.transports.Console({
      formatter: (options) => {
        const ns = getNamespace('application');

        const requestId = ns ? ns.get('requestId') : '';
        const logLevel = options.level.toUpperCase();
        const time = moment();
        const message = options.message || '';

        return JSON.stringify({
          timestamp: time.toISOString(),
          logLevel,
          message,
          requestId,
          service: 'Microservice B'
        });
      }
    })
  ]
});