From Rails to Syslog or: How I Learned to Stop Worrying and Ditch production.log

In my previous installment I ranted about. among other things, the way Rails suggests you to keep a world-writeable log file for the production environment. As I said at the end, I planned on looking at the syslogger gem and that was actually quite helpful.

The idea goes like this: by using syslogger you can tell Rails that the logs have to go through the syslog; in my case that means it goes to metalog, which then filters on the webapp names and pushes it to /var/log/rails, taking care of rotating the log as needed (either due to size or time — the former is quite useful to avoid that rogue bots cause a DoS, which happened to me when I was inexperienced with these technologies!). Of course, this only works on Unix, but that’s what I care about anyway.

Beside the placement of the logs, using metalog for me also means I can filter important messages and show them in the important messages’ log rather than being just limited to a hidden log file within the app’s own tree, and also means that I can mix in the messages of all the running applications, rather than having each report to a different file. If I were to use syslog-ng instead, I could easily make it send the logs via network to another box and aggregate all of them there… but I really don’t see the point (yet) for that, and the features that metalog comes with tramp easily the network support.

So how do you achieve this? It’s actually pretty easy. Obviously it starts with installing dev-ruby/syslogger (in Gentoo, through Portage, everywhere else, via gem); then you can configure this very easily on both Rails 2.3 and 3.x series (I have one server running Rails 2.3, the other 3.1… I have yet to set up Typo 6.x, but I’ll probably do that at some point in the near future, although unlikely before FOSDEM).

The trick is all in config/environments/production.rb, where you have to tell Rails to use a custom Logger; there is already an example, commented-out like that refers to the other gem, SyslogLogger, but you should change it to something like this

  config.logger = Syslogger.new("yourappname")

This way you can distinguish each application’s messages in the log. Then in the metalog.conf file you can have:

Rails apps : 
  program_regex = "^(typo|radiant|yourappname)"
  logdir = "/var/log/rails"
  maxfiles = 5
  break = 1

so that everything is then readable as /var/log/rails/current.

I’m not sure how much it impacts performance; I’d be surprised if it decreased them, as metalog also buffers the disk writes, but you never know until you check for sure; in general I still prefer if the (multiple) Rails processes send everything to metalog for my own convenience.

Interestingly, if you have a webapp that does not deal with on-disk files directly, but just with a database, by using syslogger you’re basically limiting the writing to the cache directories only, which is probably a positive note.

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