Is Bunyan log.child the right use case?

Question

I watched bunyan to enter my nodejs application. I tried, and everything seems to work very well. I skipped the section on log.child , but now I'm trying to figure out how to use it. I think the goal is to allow me to provide some kind of special identifier for the journal entry so that I can uniquely identify how this journal is associated with any other journal entry.

If that were the case, I would suggest that I use log.child in every request:

 var bunyan = require('bunyan'); var log = bunyan.createLogger({name: 'myapp'}); router.post('/submit', function(req, res) { var logChild = log.child({reqId: uuid.v4()}); logChild.info({ req:req }, req.user.name + ' has called /submit'); saveData(req) .then(function(data) { logChild.info({data: data}, req.user.name + ' has saved to DB successfully in /submit'); res.json({'success': 'Saved!'}); }) .error(function(err) { logChild.error({ err: err }, req.user.name + ' has caused an error in /submit '); res.status(500).json("error": err}); }); }); 

Thus, if the user Bob POSTs before /submit twice within 30 seconds, there will be some context that distinguishes between two different calls in the log file.

That is, I will see something like this (with context):

 Bob has called /submit uuid: 109156be-c4fb-41ea-b1b4-efe1671c5836 Bob has called /submit uuid: 49dlsd7i-dapd-fdio-fei0-sd59fd0ph34d Bob has saved to DB successfully in /submit uuid: 109156be-c4fb-41ea-b1b4-efe1671c5836 Bob has caused an error in /submit uuid: 49dlsd7i-dapd-fdio-fei0-sd59fd0ph34d 

Instead (without context):

 Bob has called /submit Bob has called /submit Bob has saved to DB successfully in /submit Bob has caused an error in /submit 

So, for all my routes in my Nodejs application, I would create a logChild object and then use logChild to write entries in that route.

I got it right and implementation of the use log.child ?

Answer 1

You seem to be using log.child accordingly. One suggestion I could make to help you “uniquely identify how this log is associated with any other log entry” is to bind log to the req object. Thus, if you have other middleware, you can access the same log with the same unique identifier from several places. For instance:

 var log = bunyan.createLogger({name: 'myapp'}); router.use(function(req, res, next) { req.log = log.child({ user : req.user.id }); }); router.post('/submit', function(req, res) { req.log.info('submitted request at ' + Date.now()); }); 

Now you will see { user : some_user_id, msg: 'submitted request at 01/03/15' } in your logs, which makes it possible to link any middleware in the request chain with one user using the req.log object.