Service-Logger

A simplified Winston wrapper for microservices :)

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Overview

This module is a wrapper around Winston meant to simplify, but not limit, how business logic does its logging. The class exposed by this module provides convenient functionality wrapped around basic Winston functionality that should be needed by microservices in most cases.

For special cases it also exposes the winston module itself and the user can extend and interact with Winston as they would normally. However, in these cases it is important that the user understands how to use Winston as well as the source code in this project to avoid unexpected behavior.

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Usage

#### ! ! IMPORTANT ! !

Before using the logger, read all information below.

1. process.env.LOG_LEVEL
   In order for the Logger to work as you intend, you should set the process.env.LOG_LEVEL environment variable. It must be set to the maximum level of messages you want the Logger to log. The level should be one of the RFC5424 syslog Severity level keywords. All instances of this wrapper Logger class will use this value specified.

• If LOG_LEVEL not set, the Logger will only log levels info and higher.
• If LOG_LEVEL=* everything will be logged. (debug and higher).
• If LOG_LEVEL=INFO levels info and higher will be logged.
• If LOG_LEVEL=INFO,WARNING you will get an error because you can only set one value.
  
  

2. Request ID
   It can be useful to add a request ID to log entries to make tracking request chains and debugging easier. This logger gives you 2 options for adding a request ID to a log entry:

• The request-context node package is utilized by this Logger to add a request id to the log entry if if found in the request context request:requestId key.
• Adding a requestId field to the metadata object of a log entry.
  
  See Examples below for log entries with request IDs included!
  
  

3. Log Source Path
   When instantiating the Loggers there is one argument to pass to the constructor: sourcePath.
   This value will be used to show the source of the log statement, whether it be a filepath or a custom value.
   It is recommended that you pass __filename (not a string, the Node __filename var!) because the Logger will show filepaths of the files producing the log statements relative to the root of the application. If you specify something other than a valid filepath like __filename (e.g. 'my:custom:module:path'), the logger will just display that instead.
   See Examples below

How to Log

In each file you want to log in, instantiate a new logger.

const logger = new (require('service-logger'))(__filename);

NOTE: Regardless of how many times you instantiate loggers, only one static Winston Logger will be created. This Winston logger will only log to the console (console Transport). If you wish to add more Transports then you will need to get the winston instance and the Winston Logger from this module. If this is necessary then make sure you are familiar with the source code of this project as well as Winston.

const winston = logger.getWinstonInstance();
const winstonLogger = logger.getWinstonLoggerInstance();
winstonLogger.add(winston.transports.File, {
  name: 'additional_transport_log_example',
  filename: 'additional_transport_log_example.log'
});

Use the Logger! From the source code documentation:

/**
Main logging function.
@param {string} level - RFC5424 syslog Severity level keyword to use
@param {string|Error} message - main log message or Error object
@param {Object} [metadata] - object containing any additional information
you wish to log
*/
log(level, message, metadata) {
     ...
}

Examples

At the top of each file you will use the logger in:

const logger = new (require('service-logger'))(__filename); // recommended!

or

const logger = new (require('service-logger'))('my:custom:module:path');

Logging a message:

logger.<RFC5424 syslog Severity level keyword>('Message');

logger.info('Basic test');

> 2017-11-08T18:46:24.209Z - info - test/test.js - Basic test

Logging a message with a request id:

requestContext.set('request:requestId', 12345678) // this would be called at beginning of request using middleware
...
...
logger.notice(`Show the request id`, { otherMetadata: 'yay' });

> 2017-11-08T18:46:24.210Z - notice - test/test.js - 12345678 - Show the request id {"otherMetadata":"yay"}


-- OR --


logger.notice(`Show the request id`, { requestId: '12345678', otherMetadata: 'yay' });

> 2017-11-08T18:46:24.210Z - notice - test/test.js - 12345678 - Show the request id {"requestId":"12345678","otherMetadata":"yay"}

Logging an Error object

const appError = new Error('Uh oh!');

logger.err(appError);