如何将Winston限制为每个日志文件仅1个文件描述符

Question

I'm currently using Winston in my project to log to a handful of log files - 4 different files to be exact. Each file is leveraged by a large number of classes to group specific functionality - a pretty typical use case for an application. My problem is that as of now, Winston is opening up a separate file descriptor for the same log file for every single class, every single time the class is even used. I'm running on the most recent version of Amazon Linux and my baseline is 470 file descriptors in use. As soon as I start up my application, I jump to over 1700. From there, thousands of additional file descriptors are used as the app runs and instantiates new classes that utilize the loggers. All our logs are pulled in using Winston's container (see code below).

Update: I just created a barebones app with ONLY winston, and I used it to create 1 parent logger and thousands upon thousands of child loggers. I'm also using the child loggers to log a message when they're created. This whole process only takes 1 file descriptor on the OS, so clearly something we're doing in our app (it's far more complex) is causing Winston to open a separate FD...but that's not the default behavior. Has anyone seen this before? I am working on adding more and more to the test app just to see if I can find the point when it actually starts using more file descriptors.

Answer 1

We have the method to retrieve a logger set up to be static, and so I'm starting to think that is the issue.

This only means that the class doesn't have to be instantiated to run that method. It has no bearing on the lifetime of the return value.

The way I handle this is with a simple script where I export the Winston instance. For example:

const winston = require('winston');

const applog = winston.createLogger({
  transports: [
    new (winston.transports.Console)({ 
      level: 'debug',
      handleExceptions: true
    })
  ],
  format: winston.format.simple()
});

module.exports = applog;

Then, in any module where I want the logger, something like this:

const applog = require('./lib/applog');

Node.js caches the result of require() , so whatever you export is guaranteed to be the exact same instance for anywhere that the module is required.

You can adapt this method to your class and static method if you'd like. Just do all of your Winston setup outside of the class (in that same file), and have the static method return the instance.

Answer 2

Well now I just feel stupid. The issue had nothing to do with child loggers at all, creating a child logger definitely does not open a new file descriptor. The issue was that we were always passing logger options to our loggers.get(id, options) method, rather than just passing the id with no options if the logger already existed. The fix took all of a few lines of code and now we only have 1 file descriptor open per log file. D'oh!