How to flush winston logs? - node.js

Question

I want to flush the winston logger before process.exit.
process.on('uncaughtException', function(err){
logger.error('Fatal uncaught exception crashed cluster', err);
logger.flush(function(){ // <-
process.exit(1);
});
});
Is there anything like logger.flush available? I couldn't find anything about it, other than people complaining about winston not being very actively maintained.
As an alternative, is there any popular (actively maintained) multi-transport logging framework that provides a flushing capability?

Answer 1

Winston actually allows you to pass in a callback which is executed when all transports have been logged:
process.on('uncaughtException', function(err) {
logger.log('error', 'Fatal uncaught exception crashed cluster', err, function(err, level, msg, meta) {
process.exit(1);
});
});
Docs: https://github.com/flatiron/winston#events-and-callbacks-in-winston

Answer 2

Unfortuantely, Winston will sometimes call the logging callback before the transport has had a chance to flush, so the accepted answer can still lead to un-saved log messages (especially on the first turn of the event loop). A better solution is implemented in the winston-log-and-exit package / patch.

Answer 3

Calling process.exit inside the log-callback like Thomas Heymann suggested will not ensure that the logs are actually flushed, especially when using a File-transport.
Instead of calling process.exit directly I would let the logger call process.exit after the log was flushed:
logger.js :
var winston = require('winston');
winston.loggers.add('my-logger', {
console: {
level: 'debug',
colorize: true,
timestamp: true,
handleExceptions: true
},
file: {
level: 'info',
colorize: false,
timestamp: true,
filename: file,
handleExceptions: true
}
});
var logger = winston.loggers.get('my-logger');
/* ******* *
* EXPORTS
* ******* */
exports.exitAfterFlush = function(code) {
logger.transports.file.on('flush', function() {
process.exit(code);
});
};
exports.info = function() {
logger.info.apply(this, arguments);
};
exports.warn = function() {
logger.info.apply(this, arguments);
};
exports.error = function() {
logger.info.apply(this, arguments);
};
And in your code:
var logger = require('./logger.js');
logger.exitAfterFlush(0);
info('Done!');
Tested on NodeJS v4.1.2 and winston 1.1.0

Answer 4

This may help someone. logger is an instance of winston.createLogger which defines two transports (console & file). The exit code is reflected in the shell.
const logger = require('../library/log');
function exitAfterFlush() {
logger.on('finish', function () {
logger.end();
});
};
process.on('exit', (code) => {
console.log(`About to exit with code: ${code}`);
});
logger.info(`Started with PID:${process.pid}`);
logger.error(`*****`);
process.exitCode = 11;
exitAfterFlush();

Answer 5

Winston has a better way to deal with this exceptions.
var logger = new (winston.Logger)({
transports: [
new winston.transports.File({ filename: 'path/to/all-logs.log' })
],
handleExceptions: true,
exceptionHandlers: [
new winston.transports.File({ filename: 'path/to/exceptions.log' })
]
});