Pipe log data to a stream, fuggetabout rotation


A Writable Stream that supports linux logrotate style options


On the command line:

  node app.js 2>&1 | logrotate-stream app.log --keep 3 --size '50m' --compress

As a module:

var stream = require('logrotate-stream')
  , toLogFile = stream({ file: './test.log', size: '100k', keep: 3 });

the problem

Rotating logs that are being written to with stdio redirection sucks. Using a utility like logrotate doesn't automagically update your processes log file descriptor and you end up with several empty logs and one mega rotated log.

There's a couple ways to try and deal with this, but they all fall short:

This requires adding a new dependency and possibly code changes around logging logic.

Often times, production apps can't be restarted willy-nilly

This only works if you don't need to guarantee that all of your log lines are persisted. copytruncate performs a non-atomic copy before truncating the original log, which means you can lose data in the process if the copy is slow.

logrotate-stream tries to remedy this situation by acting as an intermediary between the application and the file system, piping stdin to log files and rotating those logfiles when necessary.

upstart woes

If you find yourself using logrotate-stream with upstart, there's a few things to consider. Piping to logrotate-stream in your exec line will cause upstart to track the pid of the logrotate process rather than your app. While stopping will still work (most likely emitting an EPIPE error on your app before exiting), it would be better if you used a named pipe to redirect your apps output:

chdir /path/to/app
pre-start script
  # create a named pipe
  mkfifo logpipe
  # create a backgrounded logrotate-stream process and
  # redirect the named pipe data to it
  logrotate-stream app.log --keep 3 --size 50m < logpipe &
end script
# start the app, redirecting stdout & stderr to the named pipe
exec /usr/local/bin/node index.js > logpipe 2>&1

This setup will register the correct pid with upstart, make sure your stdio is forwarded to logrotate-stream, and will properly kill the logrotate-stream process when your app is stopped.


The file log file to write data to.

The max file size of a log before rotation occurs. Supports 1024, 1k, 1m, 1g

The number of rotated log files to keep (including the primary log file). Additional logs are deleted no rotation.

Optionally compress rotated files with gzip.


With npm do:

npm install logrotate-stream